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universe-review.catitle>Multi-cell Organismsuniverse-review.ca/title>
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universe-review.caa href="form.htm" target="default.htm">universe-review.catd width="10%" align="center">universe-review.cab>Contactuniverse-review.ca/b>universe-review.ca/td>universe-review.ca/a>universe-review.ca/tr>universe-review.ca/table>
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universe-review.cah2>universe-review.cafont color="blue">Mulitcellular Organismsuniverse-review.ca/font>universe-review.ca/h2>
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universe-review.cah3>Contentsuniverse-review.ca/h3>
universe-review.caa href="universe-review.ca#classifications/default.htm#classifications/">Biological Classificationsuniverse-review.ca/a>universe-review.cabr />
universe-review.caa href="universe-review.ca#evolution/default.htm#evolution/">Evolution of Multicellular Organismsuniverse-review.ca/a>universe-review.cabr />
universe-review.caa href="universe-review.ca#lifecycles/default.htm#lifecycles/">Sexual Life Cyclesuniverse-review.ca/a>universe-review.cabr />
universe-review.caa href="universe-review.ca#Hoxgenes/default.htm#Hoxgenes/">Homeobox Genesuniverse-review.ca/a>universe-review.cabr />
universe-review.caa href="universe-review.ca#germlayers/default.htm#germlayers/">The Three Germ Layers and Organsuniverse-review.ca/a>universe-review.cabr />
universe-review.caa href="universe-review.ca#stemcells/default.htm#stemcells/">Stem Cellsuniverse-review.ca/a>universe-review.cabr />
universe-review.caa href="universe-review.ca#cloning/default.htm#cloning/">Cloninguniverse-review.ca/a>universe-review.cabr />
universe-review.caa href="universe-review.ca#sexanddeath/default.htm#sexanddeath/">Sex and Deathuniverse-review.ca/a>universe-review.cabr />
universe-review.caa href="universe-review.ca#clock/default.htm#clock/">Biological Clockuniverse-review.ca/a>universe-review.cabr />
universe-review.caa href="universe-review.ca#brain/default.htm#brain/">The Brainuniverse-review.ca/a>universe-review.cabr />
universe-review.caa href="universe-review.ca#sleep/default.htm#sleep/">Sleep and Dreamuniverse-review.ca/a>universe-review.cabr />
universe-review.caa href="universe-review.ca#meditation/default.htm#meditation/">Meditationuniverse-review.ca/a>universe-review.cabr />
universe-review.caa href="universe-review.ca#consciousness/default.htm#consciousness/">Consciousnessuniverse-review.ca/a>universe-review.cabr />
universe-review.caa href="universe-review.ca#fungi/default.htm#fungi/">Fungiuniverse-review.ca/a>universe-review.cabr />
universe-review.caa href="universe-review.ca#plants/default.htm#plants/">Plantsuniverse-review.ca/a> (universe-review.caa href="R10-23-plants.htm">Cambrian - presentuniverse-review.ca/a>) universe-review.cabr />
universe-review.caa href="universe-review.ca#animals/default.htm#animals/">Animalsuniverse-review.ca/a> (universe-review.caa href="R10-19-animals.htm">Cambrian - presentuniverse-review.ca/a>) universe-review.cabr />
universe-review.caa href="universe-review.ca#humans/default.htm#humans/">What Makes Us Humansuniverse-review.ca/a>universe-review.cabr />
universe-review.caa href="universe-review.ca#model/default.htm#model/">Future of the Human Raceuniverse-review.ca/a>universe-review.cabr />
universe-review.caa href="universe-review.ca#footnotes/default.htm#footnotes/">Footnotesuniverse-review.ca/a>universe-review.cabr />
universe-review.caa href="universe-review.ca#references/default.htm#references/">Referencesuniverse-review.ca/a>universe-review.cabr />
universe-review.caa href="universe-review.ca#Index/default.htm#Index/">Indexuniverse-review.ca/a>universe-review.cabr />
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universe-review.cah3 align="center">universe-review.caa name="classifications">Biological Classificationsuniverse-review.ca/a>universe-review.ca/h3>
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universe-review.catd width="25%">universe-review.caa href="I10-01-FiveKingdom.jpg">universe-review.caimg src="I10-01-FiveKingdom.jpg" name="Five Kingdom" alt="Five Kingdom" align="left" width="175"/>universe-review.ca/a>universe-review.ca/td>
universe-review.catd width="25%">universe-review.caa href="I10-02-TreeOfLife.jpg">universe-review.caimg src="I10-02-TreeOfLife.jpg" name="Tree of Life" alt="Tree of Life" align="left" width="250"/>universe-review.ca/a>universe-review.ca/td>
universe-review.catd width="50%">Biology used to classify living organisms into universe-review.caA NAME="kingdoms">universe-review.ca/A>five kingdoms as shown in Figure 10-01. They include universe-review.caA NAME="prokaryotes">universe-review.ca/A>prokaryotes (no nucleus, no organelles), universe-review.caA NAME="protista">universe-review.ca/A>universe-review.caa href="F11-monocell.htm#protista">protistauniverse-review.ca/a> (possess universe-review.caa href="R10-01-cellnucleus.htm">nucleusuniverse-review.ca/a> and universe-review.caa href="R10-02-cellorganelle.htm">organellesuniverse-review.ca/a>), fungi, plants, and animals. The time scale (in billions of years) is referred to the appearance of oldest fossils. Study of DNA variation among different species provides another way to classify them as shown by the universe-review.caA NAME="etree">universe-review.ca/A>tree of life in Figure 10-02a. According to this scheme the common ancestor at the base of the tree gave rise to three branches: universe-review.ca/td>universe-review.ca/tr>
universe-review.catr>universe-review.catd width="25%">universe-review.cah4>Figure 10-01 Kingdoms universe-review.caa href="I10-01-FiveKingdom.jpg">[view large image]universe-review.ca/a>universe-review.ca/h4>universe-review.ca/td>
universe-review.catd width="25%">universe-review.cah4>Figure 10-02a Tree of Life universe-review.cabr />universe-review.caa href="I10-02-TreeOfLife.jpg">[view large image]universe-review.ca/a>universe-review.ca/h4>universe-review.ca/td>
universe-review.catd width="50%">microbes known as universe-review.caA NAME="archaea">universe-review.ca/A>universe-review.caa href="F11-monocell.htm#archaebacteria">archaeauniverse-review.ca/a> (primitive unicellular organisms that live in most extreme environments),
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universe-review.caA NAME="bacteria">universe-review.ca/A>universe-review.caa href="F11-monocell.htm#bacteria">bacteriauniverse-review.ca/a> (unicellular organisms without nucleus or universe-review.caa href="I10-05-cellorganelle.jpg">cell structureuniverse-review.ca/a>), and universe-review.caA NAME="eukaryotes">universe-review.ca/A>eukaryotes (any organism with one or more cells that have visible nucleus and organelles). The lengths of the branches reflect how much the DNA of each lineage has diverged from their common ancestor. They demonstrate that most of life's genetic diversity turns out to be microbial; the entire animal kingdom (shown at the upper right) are just a few twigs at one end of the tree. It is obvious that multicellular organisms such as fungi, plants and animals evolved from unicellular organisms further down the tree.
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universe-review.catd width="20%">universe-review.caa href="I10-02-TreeOfLife2.jpg">universe-review.caimg src="I10-02-TreeOfLife2.jpg" name="Tree of Life" alt="Tree of Life" align="left" width="200"/>universe-review.ca/a>universe-review.ca/td>
universe-review.catd width="20%">universe-review.caa href="I10-02-TreeOfLife3.jpg">universe-review.caimg src="I10-02-TreeOfLife3.jpg" name="Tree of Life" alt="Tree of Life" align="left" width="185"/>universe-review.ca/a>universe-review.ca/td>
universe-review.catd width="60%">Recently, new evidence suggests that the Tree of Life may be more complicated than the version shown in Figure 10-02a. The revised version indicates that early life may not have existed as distinct species; instead they may have traded their genes promiscuously. Life may descend from a huge primordial menagerie rather than from a single common ancestor. Billions of years later, after the three branches split apart, distantly related species still joined universe-review.ca/td>universe-review.ca/tr>
universe-review.catr>universe-review.catd width="20%">universe-review.cah4>Figure 10-02b Tree of Life, Reviseduniverse-review.caa href="I10-02-TreeOfLife2.jpg">[view large image]universe-review.ca/a>universe-review.ca/h4>universe-review.ca/td>
universe-review.catd width="20%">universe-review.cah4>Figure 10-02c Ring of Life universe-review.caa href="I10-02-TreeOfLife3.jpg">[view large image]universe-review.ca/a>universe-review.ca/h4>universe-review.ca/td>
universe-review.catd width="60%">together sometimes, as bacteria were swallowed up by other organisms. Two of these fusions - bacteria giving rise to mitochondria and chloroplasts - are shown in the new Tree of Life (Figure 10-02b).
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In view of such common practices of lateral gene transfer and endosymbiosis, it is proposed in 2004 that the the tree of life should be replaced by the ring of life as shown in Figure 10-02c. In this diagram, the eukaryotes plus the eukaryotic root organisms comprise the eukaryotic realm on the left-hand side. Ancestors defining major groups in the prokaryotic realm are indicated by small circles on the ring. The archaea, shown on the right, includes the euryarchaea, and the eocyta.
universe-review.cabr />universe-review.cabr />The time scale derived from fossil records is usually calculated from radioactive dating. For example in carbon-14 dating, the fact that the ratio of Cuniverse-review.casup>14universe-review.ca/sup> to Cuniverse-review.casup>12universe-review.ca/sup> is fairly constant (~ 10universe-review.casup>-12universe-review.ca/sup>) in living organisms and that Cuniverse-review.casup>14universe-review.ca/sup> is radioactive with a universe-review.caa href="R01-04-diffeq.htm#halflife">halflifeuniverse-review.ca/a> of about 5730 years, would yield the age of the organism since its death (no more accumulation of Cuniverse-review.casup>14universe-review.ca/sup>) if we measure the leftover amount of Cuniverse-review.casup>14universe-review.ca/sup> in the sample. The DNA variation (between species) shows only the genetic difference, which can be calibrated with known time difference from fossil records. However, this calibration can be extrapolated to the unknown region only if the rate of DNA base substitution (the molecular clock) is constant. Unfortunately, it is found that genes change (mutate) at different rates.
universe-review.caa href="default.htm#top/">universe-review.cah4>[Top]universe-review.ca/h4>universe-review.ca/a>
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universe-review.cah3 align="center">universe-review.caa name="evolution">Evolution of Multicellular Organismsuniverse-review.ca/a>universe-review.ca/h3>
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universe-review.catd width="30%">universe-review.caa href="I10-03-evolution1.jpg">universe-review.caimg src="I10-03-evolution1.jpg" name="Evolution Sequence" alt="Evolution Sequence" align="left" width="300"/>universe-review.ca/a>universe-review.ca/td>
universe-review.catd width="30%">universe-review.caa href="I10-03-evolution2.jpg">universe-review.caimg src="I10-03-evolution2.jpg" name="Evolution Sequence" alt="Evolution Sequence" align="left" width="270"/>universe-review.ca/a>universe-review.ca/td>
universe-review.catd width="40%">Figure 10-03 reconstructs the evolution of the multi- cellular organisms. Water-based life evolved first as illustrated in the bottom half of the picture, land-based life appeared later as shown in the top half.
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universe-review.catr>universe-review.catd width="30%">universe-review.cah4>Figure 10-03 Evolutionary Sequence universe-review.ca/h4>universe-review.ca/td>
universe-review.catd width="30%">universe-review.cah4>universe-review.caa href="I10-03-evolution1.jpg">[view large image1]universe-review.ca/a> universe-review.caa href="I10-03-evolution2.jpg">[view large image2]universe-review.ca/a>universe-review.ca/h4>universe-review.ca/td>
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universe-review.catd width="30%">universe-review.caa href="R10-03-multicell.htm">universe-review.caimg src="I10-06-multicell.jpg" name="Multicellularity" alt="Multicellularity" align="left" width="300"/>universe-review.ca/a>universe-review.ca/td>
universe-review.catd width="70%">universe-review.caA NAME="multicellurity">universe-review.ca/A>Multicellular organisms have arisen independently a number of times starting from about 1.5 billion years ago. Thirteen separate inventions of multicellurity are indicated in Figure 10-04. The attempt to become multicellular seems to happen by chance, e.g., the pair of cells failed to separate during cell division, or two cells stuck together accidentally. If natural selection favoured this new form, it would survive and prosper. The advantage can be varied. It could be for better dispersal of spore (by a long stalk), for staying in one place (with a root), more efficient feeding, or for confronting predator. A living example of the attemps to become multicelluar organism is represented by the universe-review.caa href="R10-18-slimemoulds.htm">slime mouldsuniverse-review.ca/a>, which transform from single cells to one multicelluar organism under adverse condition. Natural selection works in two ways on the life cycles of all organisms. There is a selection pressure for size increaseuniverse-review.casup>universe-review.caa href="universe-review.ca#one/default.htm#one/">1universe-review.ca/a>universe-review.ca/sup> under innumerable ecological circumstances, and becoming multicellular is an easy way to accomplish this. At the same time, there is a selection to retain a single-cell stage in the life cycle. This is a requirement for sexual reproductionuniverse-review.casup>universe-review.caa href="universe-review.ca#two/default.htm#two/">2universe-review.ca/a>universe-review.ca/sup>, for universe-review.caA NAME="meiosis">universe-review.ca/A>universe-review.caa href="R10-12-meiosis.htm">meiosisuniverse-review.ca/a> and fertilization can only be achieved in a unicellular stage in eukaryotic organisms. The reason has to do with the way the genetic material is incorporated into chromosomes, and with the
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universe-review.catr>universe-review.catd width="30%">universe-review.cah4>Figure 10-04 Multicellularity universe-review.cabr />universe-review.caa href="R10-03-multicell.htm">[view large image]universe-review.ca/a>universe-review.ca/h4>universe-review.ca/td>
universe-review.catd width="70%">separation and recombination (crossover) of the universe-review.caA NAME="allelic">universe-review.ca/A>universe-review.caa href="R10-14-alleles.htm">allelesuniverse-review.ca/a> (two versions of the same gene) at meiosis. Furthermore, the fusion of the genes from two parents can only take place in single cell.
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universe-review.caa href="default.htm#top/">universe-review.cah4>[Top]universe-review.ca/h4>universe-review.ca/a>
universe-review.cahr align="center" width="15%" />
universe-review.cah3 align="center">universe-review.caa name="lifecycles">Sexual Life Cyclesuniverse-review.ca/a>universe-review.ca/h3>
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universe-review.catd width="30%">universe-review.caa href="I10-07-lifecycle.jpg">universe-review.caimg src="I10-07-lifecycle.jpg" name="Life Cycle of Animals" alt="Life Cycle of Animals" align="left" width="300"/>universe-review.ca/a>universe-review.ca/td>
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This leads to a paradox of cosmic implications: natural selection is simultaneously pushing for a large stage in the life cycle that can compete for food and for a minute single-cell stage that is essential for sexual reproduction. The result is that all multicellular organisms, from small algae and fungi to elephants and human, have a unicellular stage and a large stage of varying dimensions in their life cycle. Figure 10-05 shows the life cycle of animals for which the unicellular stage is the universe-review.caA NAME="gamete">universe-review.ca/A>gamete in the form of egg or sperm. This is called the universe-review.caA NAME="haploid">universe-review.ca/A>haploid state where a single cell carries n chromosomes after meiosis (cell division that transmits only n chromosomes) The large stage is the universe-review.caA NAME="diploid">universe-review.ca/A>diploid state comprised with all the somatic cells in the rest of the body. Those cells carry 2n chromosomes (one from each parent at fertilization) starting from the universe-review.caA NAME="zygote">universe-review.ca/A>zygote. They can differentiate into different cell types (performing different function) during universe-review.caA NAME="mitosis">universe-review.ca/A>mitosis (cell division in which the daughter cells receive the exact chromosome and genetic makeup of the mother cell). universe-review.cabr />
universe-review.caa href="I10-07-lifecycle.jpg">[view large image]universe-review.ca/a>
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universe-review.catr>universe-review.catd width="30%">universe-review.cah4>Figure 10-05 Life Cycle of Animalsuniverse-review.ca/h4>universe-review.ca/td>
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universe-review.ca/td>universe-review.ca/tr>universe-review.ca/table>
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universe-review.catd width="25%">universe-review.caa href="I10-08-plantlife.jpg">universe-review.caimg src="I10-08-plantlife.jpg" name="Life Cycle of Plants" alt="Life Cycle of Plants" align="left" width="200"/>universe-review.ca/a>universe-review.ca/td>
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Animal life cycle has the adult (the multicellular form) always in diploid state. However, this is not the case in more primitive species. Figure 10-06 shows the relative importance of the diploid and haploid generations among plants. Mosses are primitive plants, they still require very wet conditions for growth and fertilization. Meiosis produces universe-review.caA NAME="spores">universe-review.ca/A>spores, which germinate into universe-review.caA NAME="gametophyte">universe-review.ca/A>gametophyte (male and female adults in haploid state). The gymnosperms (conifers) and angiosperms (flowering plants) are more advanced; the adult is in diploid state. This evolutionary development seems to indicate that earlier life tried to construct the multicellular body from the simpler cell unit in haploid state. It was switched gradually to the more stable diploid state where two similar copies of the genes are available - a primary and a backup.universe-review.ca/td>universe-review.ca/tr>
universe-review.catr>universe-review.catd width="25%">universe-review.cah4> Figure 10-06 Life Cycle ofuniverse-review.ca/h4>universe-review.ca/td>
universe-review.catd width="75%">universe-review.cah4>Plants universe-review.caa href="I10-08-plantlife.jpg">[view large image]universe-review.ca/a>universe-review.ca/h4>
universe-review.ca/td>universe-review.ca/tr>universe-review.ca/table>
universe-review.caa href="default.htm#top/">universe-review.cah4>[Top]universe-review.ca/h4>universe-review.ca/a>
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universe-review.cah3 align="center">universe-review.caa name="Hoxgenes">Homeobox Genesuniverse-review.ca/a>universe-review.ca/h3>
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Multicellular organism development involves many processes as illustrated in the simple case of universe-review.caa href="R10-18-slimemoulds.htm">slime mouldsuniverse-review.ca/a>. These include chemical signal, chemical gradient, cellular adhesion, anterior-posterior polarity, pattern formation, cell movement, and cell differentiation. Multicellular organisms in higher form have all these functions achieved under the direction of the homeobox genesuniverse-review.casup>universe-review.caa href="universe-review.ca#three/default.htm#three/">3universe-review.ca/a>universe-review.ca/sup>, which manifests itself at an early stage of embryonic universe-review.caA NAME="embryonic">universe-review.ca/A>development and determines body shape.
Humans, worms and flies don't look very similar and they universe-review.ca/td>universe-review.catd width="2%"> universe-review.ca/td>universe-review.catd width="49%">do not go through the same developmental stages. Yet the genes that control their body shape and organization are
related in sequence. These genes all share a common segment called the homeobox. This 180 nucleotide sequence codes for 60 amino acidsuniverse-review.casup>universe-review.caa href="universe-review.ca#four/default.htm#four/">4universe-review.ca/a>universe-review.ca/sup> found in a proteins called universe-review.caA NAME="homeodomain">universe-review.ca/A>homeodomain. The rest of the proteins may be very different, but this 60 amino acid piece is crucial for their function. The homeodomain controls the activities of other genes. Mutation in hox gene usually cause abnormal growth.universe-review.ca/td>universe-review.ca/tr>universe-review.ca/table>
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universe-review.catd width="20%">universe-review.caa href="I10-10-hox1.jpg">universe-review.caimg src="I10-10-hox1.jpg" name="Hox Genes" alt="Hox Genes" align="left" width="170"/>universe-review.ca/a>universe-review.ca/td>
universe-review.catd width="20%">universe-review.caa href="I10-10-hox2.jpg">universe-review.caimg src="I10-10-hox2.jpg" name="HomeoDomain" alt="HomeoDomain" align="left" width="170"/>universe-review.ca/a>universe-review.ca/td>
universe-review.catd width="20%">universe-review.caa href="I10-10-hox3.jpg">universe-review.caimg src="I10-10-hox3.jpg" name="HoxEmbryo" alt="HoxEmbryo" align="left" width="125"/>universe-review.ca/a>universe-review.ca/td>
universe-review.catd width="40%">Figure 10-07 depicts the genes for the development of various regions (coded in different colours) in the fruit fly (universe-review.caspan style="font-style: italic">Drosphilauniverse-review.ca/span>), mouse, and human. The genes are clustered in the chromosome in the exact order as shown. They are expressed in the same order of this spatial sequence, which is also the temporal order of expression. Each of this gene has the 180 nucleotide sequence codes embedded. These sequence of 180 DNA codes differs only slightly in different
universe-review.ca/td>universe-review.ca/tr>
universe-review.catr>universe-review.catd width="20%">universe-review.cah4>Figure 10-07 Hox Genesuniverse-review.caa href="I10-10-hox1.jpg">[view large image]universe-review.ca/a>universe-review.ca/h4>universe-review.ca/td>universe-review.catd width="20%">universe-review.cah4>Figure 10-08 HomeoDomainuniverse-review.cabr />universe-review.caa href="I10-10-hox2.jpg">[view large image]universe-review.ca/a>universe-review.ca/h4>universe-review.ca/td>universe-review.catd width="20%">universe-review.cah4>Figure 10-09 Early Developmentuniverse-review.cabr />universe-review.caa href="I10-10-hox3.jpg">[view large image]universe-review.ca/a> universe-review.ca/h4>universe-review.ca/td>universe-review.catd width="40%">gene. The corresponding proteins are shown in Figure 10-08. The homeodomains are the highly similar 60-amino acid regions of the proteins made by all homeobox universe-review.ca/td>universe-review.ca/tr>universe-review.ca/table>
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genes. Each letter in the consensus string represents an amino acid. Deviation from that consensus are shown for some of the homeobox proteins in universe-review.caspan style="font-style: italic">Drosphilauniverse-review.ca/span> (upper row) and mouse (lower row). Figure 10-09 shows the gradually diversified development of the universe-review.caA NAME="embryo">universe-review.ca/A>embryo across species from fruit fly to fish, slamander, chicken, rabbit, and human. It reveals that despite the differences in the final appearance of the animals, universe-review.ca/td>universe-review.catd width="2%"> universe-review.ca/td>universe-review.catd width="49%">they use closely related genes to specify parts of the body along the anterior-posterior (head-tail) axis in the very early stage. It is believed that the developments of limbs and other specialized parts are controlled by universe-review.caA NAME="retinoic">universe-review.ca/A>retinoic acid (a version of vitamin A) gradient as the substance diffuses from a source. The hox genes response differently according to the concentration of the retinoic acid.universe-review.ca/td>universe-review.ca/tr>universe-review.ca/table>
universe-review.cabr />universe-review.cabr />The importance of universe-review.caA NAME="gradient">universe-review.ca/A>universe-review.caa href="R10-11-gradient.htm">Chemical gradientuniverse-review.ca/a> in embryonic development is supported by mathematical models generated from the universe-review.caA NAME="Turing">universe-review.ca/A>universe-review.caa href="I10-53-Turing.jpg">Turing equationuniverse-review.ca/a> which describes the diffusion process involving activator universe-review.ca/td>universe-review.catd width="2%"> universe-review.ca/td>universe-review.catd width="49%">molecules (to activate a cellular process) and inhibitors (that counter the effects of the activator). The mathematical models are able to reproduce realistically many complicated patterns in animals.
universe-review.caa href="default.htm#top/">universe-review.cah4>[Top]universe-review.ca/h4>universe-review.ca/a>
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universe-review.cah3 align="center">universe-review.caa name="germlayers">The Three Germ Layers and Organsuniverse-review.ca/a>universe-review.ca/h3>
universe-review.catable border="0" width="100%">universe-review.catr>
universe-review.catd width="25%">universe-review.caa href="I10-12-bodyplans1.jpg">universe-review.caimg src="I10-12-bodyplans1.jpg" name="Body Plan 1" alt="Body Plan 1" align="left" width="175"/>universe-review.ca/a>universe-review.ca/td>
universe-review.catd width="25%">universe-review.caa href="I10-12-bodyplans2.jpg">universe-review.caimg src="I10-12-bodyplans2.jpg" name="Body Plan 2" alt="Body Plan 2" align="left" width="225"/>universe-review.ca/a>universe-review.ca/td>
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universe-review.cap>universe-review.caA NAME="germlayers">universe-review.ca/A>The universe-review.caa href="I10-13-layers.jpg">three germ layersuniverse-review.ca/a> (endoderm, mesoderm and ectoderm) encompass the precursors of all structures and organs of the entire body, and are generated by a process called universe-review.caa href="I10-55-gastrulation.jpg">gastrulationuniverse-review.ca/a> (occurs at the early stage of the embryonic development).universe-review.ca/p>
universe-review.cap>Body cavities of animals become increasingly more complex as one ascends the evolutionary tree. Ctenophora and universe-review.caa name="cnidaria">universe-review.ca/a>universe-review.caa href="I10-54-cnidaria.jpg">Cnidariauniverse-review.ca/a> are diploblastic (a) and have two thin but well-differentiated tissue layers separated
universe-review.ca/td>universe-review.ca/tr>
universe-review.catr>universe-review.catd width="25%">universe-review.cah4>Figure 10-10 Body Plansuniverse-review.caa href="I10-12-bodyplans1.jpg">[view large image]universe-review.ca/a>universe-review.ca/h4>universe-review.ca/td>universe-review.catd width="25%">universe-review.cah4>Figure 10-11 Alternate Viewuniverse-review.cabr />universe-review.caa href="I10-12-bodyplans2.jpg">[view large image]universe-review.ca/a>universe-review.ca/h4>universe-review.ca/td>universe-review.catd width="50%">by mesoglea, a gelatinous material that protects the body and lines the gut. Flatworms have three primaryuniverse-review.cabr />universe-review.cabr /> universe-review.ca/td>universe-review.ca/tr>universe-review.ca/table>
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tissue layers and are triploblastic but are without an inner cavity called a coelom (b). Ectoderm is the outer tissue layer, mesenchyme and mesoderm are the middle tissue layers, and endoderm is the inner layer. Flatworms lack a circulatory system, so oxygen must be transported to their inner tissue layer by diffusion, and thus their bodies must remain flat. Animals with the next most complicated body plan have three tissue layers as well as universe-review.caA NAME="blood">universe-review.ca/A>hemocoelic, or blood, spaces between the tissue layers (c). The most complicated body plans have both hemocoelic spaces and universe-review.caA NAME="cavity">universe-review.ca/A>coelomic spaces (body cavity) lined with mesodermal tissue (d). The mesentery is a membrane that supports an organ or body part. In general, animals with only blood spaces are found in lower branches of the tree than are animals with coelomic spaces. Figure 10-10 shows these four types of body plan. Figure 10-11 shows the three types of triploblastic (three layers) at a different viewing angle.universe-review.ca/td>universe-review.catd width="2%"> universe-review.ca/td>universe-review.catd width="49%">
The ectodermis is responsible for the production of much of the sense organs, nervous system, and surface skin (among other things), while the endoderm contributes to the growth of structures such as the stomach and intestines, the lungs, endocrine glands, and the digestive glands. The middle layer is used to build muscular, skeleton, excretory, and reproductive systems. The mesoderm thus allows animals to become more organized in their structure. Cnidarians, for example, are organized mainly at the level of tissues, while those with three layers possess organs and elaborate organ systems. The body plan for the advance organisms is essentially tube-within-a-tube with the gut cavity inside the body cavity (the coelom). In our body the coelom is divided by the diaphragm and membranes into the peritoneal cavity (contains intestines and reproductive organs), pleural cavities (contain lungs), and pericardial cavity (contains heart).universe-review.cabr />universe-review.cabr />universe-review.ca/td>universe-review.ca/tr>universe-review.ca/table>
universe-review.caul>universe-review.caa name="cavity">universe-review.ca/a>Advantages of a body cavity (coelom or pseudocoelom): universe-review.cabr />universe-review.cabr />
universe-review.cali>Fluid in cavity helps distribute food, wastes, hormones, etc. from one end of animal to the other.universe-review.ca/li>
universe-review.cali>Better distribution allows animal to grow larger.universe-review.ca/li>
universe-review.cali>A place to put things, like new organs.universe-review.ca/li>
universe-review.cali>Hydrostatic skeleton- pressure makes cavity rigid.universe-review.ca/li>
universe-review.ca/ul>
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universe-review.catd width="20%">universe-review.caa href="R10-04-anatomy.htm">universe-review.caimg src="I10-13-anatomy.jpg" name="Anatomy 1" alt="Anatomy 1" align="left" width="165"/>universe-review.ca/a>universe-review.ca/td>
universe-review.catd width="20%">universe-review.caa href="R10-04-anatomy2.htm">universe-review.caimg src="I10-13-anatomy2.jpg" name="Anatomy 2" alt="Anatomy 2" align="left" width="190"/>universe-review.ca/a>universe-review.ca/td>
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universe-review.caa name="organ">universe-review.ca/a>All the universe-review.caa href="I10-35-organs.jpg">vital body organsuniverse-review.ca/a> except for the brain are enclosed within the trunk or torso. The trunk contains two large cavities separated by a muscular sheet called the diaphragm. The upper cavity, known as the thorax or chest cavity, contains the heart and lungs. The lower cavity, called the abdominal cavity, contains the stomach, intestines, liver, and pancreas, which all play a role in digesting food. Also within the trunk are the kidneys and bladder, which are part of the urinary system, and the reproductive organs, which hold the seeds of new human life. Figure 10-12a depicts the front view of the body cavity; while Figure 10-12b shows some inner organs. The three kinds of germ layers have differentiated into more than 350 different kinds of tissues and organs in adults.
universe-review.ca/td>universe-review.ca/tr>
universe-review.catr>universe-review.catd width="20%">universe-review.cah4>Figure 10-12a Anatomy, Front universe-review.caa href="R10-04-anatomy.htm">[view large image]universe-review.ca/a>universe-review.ca/h4>universe-review.ca/td>
universe-review.catd width="20%">universe-review.cah4>Figure 10-12b Anatomy, Inner universe-review.caa href="R10-04-anatomy2.htm">[view large image]universe-review.ca/a>universe-review.ca/h4>universe-review.ca/td>
universe-review.catd width="60%">universe-review.caa name="organ">universe-review.ca/a>Table 10-01 is a list of the human organ systems, together with its function, and major components. All body systems work together; none are independent.universe-review.ca/td>
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universe-review.cath>Organ Systemuniverse-review.ca/th>
universe-review.cath>Functionsuniverse-review.ca/th>
universe-review.cath>Componentsuniverse-review.ca/th>
universe-review.ca/tr>
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universe-review.catd align="center">universe-review.caa href="I10-13-circulatory.jpg">Circulatoryuniverse-review.ca/a>universe-review.ca/td>
universe-review.catd align="center">Transports nutrients, gases (Ouniverse-review.casub>2universe-review.ca/sub>, COuniverse-review.casub>2universe-review.ca/sub>), hormones and wastes through the bodyuniverse-review.ca/td>
universe-review.catd align="center">Heart, blood vessels and blooduniverse-review.ca/td>
universe-review.ca/tr>
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universe-review.catd align="center">universe-review.caa href="I10-13-digestive.jpg">Digestiveuniverse-review.ca/a>universe-review.ca/td>
universe-review.catd align="center">Breakdowns and absorbs nutrients for growth and maintenanceuniverse-review.ca/td>
universe-review.catd align="center">Mouth, esophagus, stomach, liver, pancreas, gallbladder, small and large intestinesuniverse-review.ca/td>
universe-review.ca/tr>
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universe-review.catd align="center">universe-review.caa href="I10-13-endocrine.jpg">Endocrineuniverse-review.ca/a>universe-review.cabr />(Hormonal)universe-review.ca/td>
universe-review.catd align="center">Relays chemical messages through the body for controlling physiological processesuniverse-review.ca/td>
universe-review.catd align="center">Hypothalamus, pineal, pituitary, thyroid, thymus, pancreas and adrenal glandsuniverse-review.ca/td>
universe-review.ca/tr>
universe-review.catr>
universe-review.catd align="center">universe-review.caa href="I10-13-excretory.jpg">Excretoryuniverse-review.ca/a>universe-review.ca/td>
universe-review.catd align="center">Filters out cellular wastes, toxins and excess water or nutrients from the circulatory systemuniverse-review.ca/td>
universe-review.catd align="center">Kidneys, ureters, bladder, urethra, lungs, sweat pores, and intestineuniverse-review.ca/td>
universe-review.ca/tr>
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universe-review.catd align="center">universe-review.caa href="I10-13-immune.jpg">Immuneuniverse-review.ca/a>universe-review.ca/td>
universe-review.catd align="center">Destroys or removes invading microbes, viruses; the lymphatic system also removes fat, and excess fluids from the blooduniverse-review.ca/td>
universe-review.catd align="center">Spleen, thymus, bone marrow, lymph, lymph nodes and vessels, white blood cells, T- and B- cellsuniverse-review.ca/td>
universe-review.ca/tr>
universe-review.catr>
universe-review.catd align="center">universe-review.caa href="I10-13-muscular.jpg">Musculouniverse-review.ca/a>-universe-review.caa href="I10-13-skeletal.jpg">skeletaluniverse-review.ca/a>universe-review.ca/a>universe-review.ca/td>
universe-review.catd align="center">Supports and moves organism; also protects delicate internal organs and provides attachment sites for the organsuniverse-review.ca/td>
universe-review.catd align="center">Skeletal and smooth muscles; bones, cartilage, tendons, and ligamentsuniverse-review.ca/td>
universe-review.ca/tr>
universe-review.catr>
universe-review.catd align="center">universe-review.caa href="I10-13-nerves.jpg">Nervousuniverse-review.ca/a> & universe-review.cabr />universe-review.caa href="I10-13-senses.jpg">sensoryuniverse-review.ca/a>universe-review.ca/td>
universe-review.catd align="center">Relays electrical signals, directs movement, controls physiological processes, and responses to environmentuniverse-review.ca/td>
universe-review.catd align="center">universe-review.caa href="universe-review.ca#brain/default.htm#brain/">Brainuniverse-review.ca/a>, spinal cord, peripheral nerves, universe-review.caa href="R10-16-ANS.htm">autonomic nervous systemuniverse-review.ca/a>, and the five sensesuniverse-review.ca/td>
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universe-review.catd align="center">universe-review.caa href="R10-32-genital.htm">Reproductiveuniverse-review.ca/a>universe-review.ca/td>
universe-review.catd align="center">manufactures cells for reproductionuniverse-review.ca/td>
universe-review.catd align="left">Female: ovaries, oviducts, uterus, vagina, and mammary glands; universe-review.cabr />male: testes, as deferens, seminal vesicles, penis, and prostate glanduniverse-review.ca/td>
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universe-review.catd align="center">universe-review.caa href="I10-13-respiratory.jpg">Respiratoryuniverse-review.ca/a>universe-review.ca/td>
universe-review.catd align="center">Provides gas exchange between the blood and the environmentuniverse-review.ca/td>
universe-review.catd align="center">Nose, trachea, and lungsuniverse-review.ca/td>
universe-review.ca/tr>
universe-review.ca/table>
universe-review.cah4 align="center">Table 10-01 Human Organ Systemsuniverse-review.ca/h4>
universe-review.caa href="default.htm#top/">universe-review.cah4>[Top]universe-review.ca/h4>universe-review.ca/a>
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universe-review.cah3 align="center">universe-review.caa name="stemcells">Stem Cellsuniverse-review.ca/a>universe-review.ca/h3>
universe-review.catable border="0" width="100%">universe-review.catr>universe-review.catd width="25%">
universe-review.caa href="I10-17-stemcells.jpg">universe-review.caimg src="I10-17-stemcells.jpg" name="Differentiation" alt="Differentiation" align="left" width="200"/>universe-review.ca/a>universe-review.ca/td>
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universe-review.caa href="I10-17-stemcell.jpg">universe-review.caimg src="I10-17-stemcell.jpg" name="Stem Cell" alt="Stem Cell" align="left" width="200"/>universe-review.ca/a>universe-review.ca/td>
universe-review.catd width="50%">Stem cells are primitive cells that give rise to other types of cells. Also called progenitor cells, there are several kinds of stem cells. universe-review.caA NAME="totipotent">universe-review.ca/A>Totipotent cells are considered the "master" cells of the body because they contain all the genetic information needed to create all the cells of the body plus the placenta, which nourishes the human embryo. Human cells have this capacity only during the first few divisions of a fertilized egg.
universe-review.ca/td>universe-review.ca/tr>
universe-review.catr>universe-review.catd width="25%">universe-review.cah4>Figure 10-13a Differentiation Pathway universe-review.caa href="I10-17-stemcells.jpg">[view large image]universe-review.ca/a>universe-review.ca/h4>universe-review.ca/td>
universe-review.catd width="25%">universe-review.cah4>Figure 10-13b Stem Cell Cycleuniverse-review.caa href="I10-17-stemcell.jpg">[view large image]universe-review.ca/a>universe-review.ca/h4>universe-review.ca/td>
universe-review.catd width="50%">(Research on existing human universe-review.caa href="I10-65-esc.jpg">embryonic stem celluniverse-review.ca/a> lines may be conducted with Federal support if the cell lines meet the U.S. President’s criteria which he announced on August 9, 2001. There are 69 cell lines registrated with NIH - National Institutes of Health, 15 of these are available for shipping. See universe-review.caa href="universe-review.ca#ref1/default.htm#ref1/">referenceuniverse-review.ca/a> for a review.)
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After 3 - 4 divisions of totipotent cells, there follows a series of stages in which the cells become increasingly specialized. The next stage of division results in universe-review.caA NAME="pluripotent">universe-review.ca/A>pluripotent cells, which are highly versatile and can give rise to any cell type except the cells of the placenta. At the next stage, cells become universe-review.caA NAME="multipotent">universe-review.ca/A>multipotent, meaning they can give rise to several other cell types, but those types are limited in number. An example of multipotent cells is hematopoietic cells - blood stem cells that can develop into several types of blood cells, but cannot develop into brain cells. At the end of the long chain of cell divisions that make up the embryo are "terminally differentiated" cells - cells that are permanently committed to a specific function. Figure 10-13a shows the pathway from embryonic stem cell to multipotent stem cell and on to the different type of specialized cells.
universe-review.cabr />universe-review.cabr />Multipotent stem cell is self-renewing. When the stem cell divides, one of the two daughter cells may go on to give rise universe-review.ca/td>universe-review.catd width="2%"> universe-review.ca/td>universe-review.catd width="49%">to other types of cell, whereas the other daughter cell
remains a stem cell, capable of dividing again and always giving one daughter to diversification. (See Figure 10-14b)
universe-review.cap>Blood cells in human body are replaced every 120 days. The replacement comes from the multipotent stem cell in universe-review.caA NAME="bone">universe-review.ca/A>the universe-review.caa href="I10-19-bonemarrow.jpg">bone marrowuniverse-review.ca/a>. Skin cells are shed every few weeks. The replacement comes from the multipotent stem cell at the base of the skin (universe-review.caA NAME="basal">universe-review.ca/A>the universe-review.caa href="I10-18-basallayer.jpg">basal layeruniverse-review.ca/a>). Scientists are still looking for the the neural stem cell. Its identity, location and potential remain unclear.universe-review.ca/p>
It has been long held that differentiated cells cannot be altered or caused to behave in any way other than the way in which they have been naturally committed. New research, however, has called that assumption into question. In recent stem cell experiments, scientists have been able to persuade blood cells to behave like neurons, or brain cells. universe-review.ca/td>universe-review.ca/tr>universe-review.ca/table>universe-review.cabr />universe-review.cabr />
Recent research in 2004 has located the neural stem cells in the universe-review.caa href="I10-66-nstem.jpg">subventricular zoneuniverse-review.ca/a> (SVZ). It is a principal source of adult neural stem cells in the rodent brain, generating thousands of olfactory bulb neurons every day. These neurons migrate from the SVZ to the brain region concerned with sensing smell. But such stem cells have become non-functional in adult human. The systematic decrease in the extent of adult neurogenesis during vertebrate evolution may be the result of an adaptation to keep neuronal populations with their accumulated experience for an entire lifespan. Therefore, the therapeutic transplantation of new neurons to regions of the human brain that are responsible for more advanced brain functions may be counterproductive, but their transplantation to other regions, such as the sensory or motor systems of the brain, could have enormous clinical significance. The identification of the cellular and molecular mechanisms that prevent adult neural stem cells from becoming integrated into functional neuronal networks would be a major accomplishment for repairing brain damage or lost neurons.
universe-review.caa href="default.htm#top/">universe-review.cah4>[Top]universe-review.ca/h4>universe-review.ca/a>
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universe-review.cah3 align="center">universe-review.caa name="cloning">Cloninguniverse-review.ca/a>universe-review.ca/h3>
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universe-review.catd width="15%">universe-review.caa href="I10-56-cloninga.jpg">universe-review.caimg src="I10-56-cloninga.jpg" name="DNA Cloning" alt="DNA Cloning" align="left" width="145"/>universe-review.ca/a>universe-review.ca/td>
universe-review.catd width="15%">universe-review.caa href="I10-56-cloningb.jpg">universe-review.caimg src="I10-56-cloningb.jpg" name="Embryo Cloning" alt="Embryo Cloning" align="left" width="120"/>universe-review.ca/a>universe-review.ca/td>
universe-review.catd width="25%">universe-review.caa href="I10-56-cloningc.jpg">universe-review.caimg src="I10-56-cloningc.jpg" name="Reproductive Cloning" alt="Reproductive Cloning" align="left" width="210"/>universe-review.ca/a>universe-review.ca/td>
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There are three types of cloning as depicted in Figures 10-14a, 10-14b, and 10-14c. Media report on cloning in the news usually refers to the type called reproductive cloning. In general, cloning is defined as an asexual process of producing a group of cells or molecular segments or organisms, that are genetically identical descendants of a single parent.
universe-review.ca/td>universe-review.ca/tr>
universe-review.catr>universe-review.catd width="15%">universe-review.cah4>Figure 10-14a universe-review.cabr />DNA Cloning universe-review.cabr />universe-review.caa href="I10-56-cloninga.jpg">[view large image]universe-review.ca/a>universe-review.ca/h4>universe-review.ca/td>
universe-review.catd width="15%">universe-review.cah4>Figure 10-14b universe-review.cabr />Embryo Cloning universe-review.cabr />universe-review.caa href="I10-56-cloningb.jpg">[view large image]universe-review.ca/a>universe-review.ca/h4>universe-review.ca/td>
universe-review.catd width="25%">universe-review.cah4>Figure 10-14c universe-review.cabr />Reproductive Cloning universe-review.cabr />universe-review.caa href="I10-56-cloningc.jpg">[view large image]universe-review.ca/a>universe-review.ca/h4>universe-review.ca/td>
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universe-review.ca/td>universe-review.ca/tr>universe-review.ca/table>
universe-review.caul>The three types of cloning:universe-review.cabr />universe-review.cabr />
universe-review.cali>DNA cloning - As shown in Figure 10-14a the DNA to be cloned is cut into fragments by the restriction enzymes. Such enzymes occur naturally in some bacteria, where they stop viral reproduction by cutting up viral DNA. They restrict the growth of viruses and hence the name. The fragment of DNA is inserted into a vector by DNA ligase, which is another bacterial enzyme that seals any breaks in a DNA molecule. The most common vector is universe-review.caa href="I10-71-plasmid.jpg">plasmiduniverse-review.ca/a>, which is a small ring of DNA removed from bacteria. Gene splicing is complete when a recombinant DNA (DNA containing fragments from two or more different sources) has been prepared. After the recombined plasmid is taken up by a host cell, cloning is achieved when the host cell and the recombinant DNA of the plasmid reproduce either the cloned gene or a protein product (produced by the gene).universe-review.ca/li>
universe-review.cali>Embryo cloning - It is also called therapeutic cloning. The goal is to create stem cell for medical purpose. The donor cell is either collected from the blastocyst or oocyte. Blastocyst is extracted from the fertilized egg after it has divided for 5 days, while oocyte is from unfertilized egg (thus by-passing the ethical issue) in the ovaries. These are highly versatile stem cells, which can differentiate into various types of cells. If the nucleus of the stem cell is removed and replaced by the patient's genes, then the various specialized cells produced by the altered stem cell can be transplanted to the patient without the problem of immunological rejection (see Figure 10-14b).universe-review.ca/li>
universe-review.cali>Reproductive Cloning - The concept behind reproductive cloning seems deceptively simple. By replacing the genetic material of an egg with that of a donated adult cell, it should be possible to create an exact copy of another living creature (see Figure 10-14c). Achieving this goal is another matter. There were lot of failures in mammalian cloning during the 1980s. Cloning of mammals became viable only in early 1990s and was well publicized with the birth of universe-review.caa href="I10-16-Dolly.jpg">Dollyuniverse-review.ca/a> (the cloned sheep) in 1997. It is found that reproductive cloning is an inefficient and error-prone process. Many cloned embryos are miscarried; others have abnormalities. It is estimated that only 1 to 10 per cent of cloned embryos from adult donor cells develop completely, depending on the species (more complicated organism is harder to clone). It took 277 attempts to clone Dolly the sheep; universe-review.caa href="I11-33-CopyCat.jpg">Carbon Copyuniverse-review.ca/a>, the cloned kitten, came after 86 failures. Only 33 monkey embryos have been created after 738 attempts - and none has produced a live birth.
universe-review.cap>Many cloning problems arise because of the key difference between normal fertilization and cloning. A normal fertilized egg contains genetic material from sperm and egg. When united, the genes in them turn on or off in a precise pattern that is in perfect readiness for the development of an embryo. Since clones do not undergo fertilization, this programming does not occur. When the donated adult cell is merged with the egg, the egg tries its best to reprogram - but it doesn't do very well. All the right genes are correctly reprogrammed in only a tiny minority of clones. To succeed in reproductive cloning, scientists need to understand how to reset these genetic instructions.universe-review.ca/p>
universe-review.cap>Sexual reproduction has evolved for two billion years and is the preferred mode after so many years of natural selection. It increases the rate of adaptive evolution and prevents the accumulation of deleterious (harmful) mutations. Cloning negates these advantages in favour of retaining some special characteristics of an organism. The argument is actually invalid because such characteristics are not determined by the genes alone; they are influenced by external factors such as the developmental environment (for the embryo) as well as subsequent growth and learning (i.e. wiring of the neurons) after birth.universe-review.ca/p>
universe-review.cap>In the movie "universe-review.caa href="I10-57-JurassicPark.jpg">Jurassic Parkuniverse-review.ca/a>", dinosaurs are cloned by extracting their DNA stored inside the mosquitoes (preserved in amber), with missing pieces patched up from the modern reptilian version. Scientifically, short segments of DNA has been isolated from 100-million-year-old specimen preserved in ambers - but not in such spectacular scale as presented by Hollywood.
universe-review.ca/p>universe-review.ca/li>
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universe-review.caa href="default.htm#top/">universe-review.cah4>[Top]universe-review.ca/h4>universe-review.ca/a>
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universe-review.cah3 align="center">universe-review.caa name="sexanddeath">Sex and Deathuniverse-review.ca/a>universe-review.ca/h3>
universe-review.catable border="0" width="100%">universe-review.catr>
universe-review.catd width="30%">universe-review.caa href="I10-14-threeages.jpg">universe-review.caimg src="I10-14-threeages.jpg" name="Three Ages" alt="Three Ages" align="left" width="200"/>universe-review.ca/a>universe-review.ca/td>
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universe-review.cap>The drawing in Figure 10-15 shows the three stages in the life cycle of organisms with sexual reproduction, human included - birth, growth, and ageing. Death is the final event. The evolution of sex and death is traced in the following.universe-review.ca/p>
universe-review.cap>The unicellular bacteria reproduced asexually in a simple process called fission. In this mode of reproduction, a given cell replicates its own DNA and then divides into two perfectly coequal clones of itself, each clonal offspring receiving one copy of the DNA. These cells mature and then repeat the cycle on and on ad infinitum. They are in effect universe-review.caA NAME="immortal">universe-review.ca/A>immortal. In reality, they do die as the result of accident or starvation but not the kind of mortality common to all sexually reproduced organisms. A review on the subject of ageing can be found in the universe-review.caa href="R10-27-ageing.htm">appendixuniverse-review.ca/a>.universe-review.ca/p>
universe-review.cap>For early single-cell eukaryotes reproducing sexually, sex may involve nothing more than two cells sticking together and swapping portions of their DNA in a process called universe-review.caA NAME="conjugation">universe-review.ca/A>conjugation. It is then followed by the fission of the participating cells. The new products are genetically different from the parent cells prior to conjugation. As a
universe-review.ca/td>
universe-review.catr>universe-review.catd width="30%">universe-review.cah4>Figure 10-15 The Three Ages universe-review.caa href="I10-14-threeages.jpg">[view large image]universe-review.ca/a>universe-review.ca/h4>universe-review.ca/td>
universe-review.catd width="70%">consequence, the older generation has disappeared - the new generation carrries another set of genes. universe-review.ca/p>universe-review.ca/td>universe-review.ca/tr>universe-review.ca/table>
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universe-review.cap>The more advanced single-cell eukaryotes like the universe-review.caa href="I10-15-paramecium.jpg">ciliateuniverse-review.ca/a> has a more elaborate arrangement. It segregates the chromosomes into a universe-review.caA NAME="micronucleus">universe-review.ca/A>micronucleus used exclusively for reproduction purpose and there is a macronucleus containing DNA used to direct the day-to-day operation of the cell. Haploid cells are made in the micronucleus through meiosis. After fertilization, the micronuclei of the two cells fuse, creating a diploid micronucleus which is the foundation of a new generation. In the subsequent replication, a new macronucleus is produced from the new micronucleus. And then the old macronucleus, sitting alone at one end of the cell, begins to degenerate and dies.universe-review.ca/p>
universe-review.cap>Once eukaryotes became multicellular, not only would reproductive DNA be kept in separate nuclei; it would be sequestered in just a few special cells in the body, which in humans and other animals are called universe-review.caA NAME="germcells">universe-review.ca/A>germ cellsuniverse-review.casup>universe-review.caa href="universe-review.ca#five/default.htm#five/">5universe-review.ca/a>universe-review.ca/sup>. Like micronuclei, germ cells have only one function: the transmission of DNA from one generation to the next via sexual reproduction. The rest of the cells in the body - the universe-review.caA NAME="somaticcells">universe-review.ca/A>somatic cells - receive identical sets of chromosomal DNA, but they use this DNA only to carry out the body's daily, nonreproductive functions. The somatic cells in our bodies universe-review.ca/td>universe-review.catd width="2%"> universe-review.ca/td>universe-review.catd width="49%">divide only by simple fission. They do not exchange or recombine DNA with one another - they do not undergo meiosis or have sex. The only purpose of somatic cells, from nature's point of view, is to optimize the survival and function of the true guardians of the DNA, the germ cells. While the germ cells can renew themselves through fertilization, the somatic cells would keep on accumulating errors and mutations until they cannot function anymore and diesuniverse-review.casup>universe-review.caa href="universe-review.ca#six/default.htm#six/">6universe-review.ca/a>universe-review.ca/sup>. That is, the somatic entity is disposable.universe-review.ca/p>
universe-review.cap>From a human point of view, it is our somatic selves - embedded in which are things like mind, personality, love, will - that we cherish most and that define us, to ourselves and to others. We think of reproduction as only one of many activities we can choose to engage in. We want so desperately to be more than just a vehicle for DNA. Yet somatic cells will die at the end of each generation. In the larger scheme of things, it matters not a whit that some of these somatic cells contain all that we hold most dear about ourselves. In terms of the basic process of life itself, which is the transmission of DNA from one generation to the next, all our life is just so much sound and fury, signifying certainly very little, and quite possibly nothing.universe-review.ca/p> universe-review.ca/td>universe-review.ca/tr>universe-review.ca/table>
universe-review.caa href="default.htm#top/">universe-review.cah4>[Top]universe-review.ca/h4>universe-review.ca/a>
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universe-review.cah3 align="center">universe-review.caa name="clock">Biological Clockuniverse-review.ca/a>universe-review.ca/h3>
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Organisms have evolved to co-ordinate their activities caused by the Earth's rotation, its revolution around the Sun, and the Moon's revolution around the Earth. Table 10-02 is a summary of the various types of biological rhythm. Biological cycles were thought to be passive, driven by environmental cues such as changes in light and temperature. It is only in the late 1990s that an internal-clock more or less independent of external environment was identified at molecular level. Figure 10-16a depicts the daily rhythm of a typical individual. It shows that there is a cyclic variation for most of the biological functions, which attain their high or low point at certain time each day.
universe-review.catr>universe-review.catd width="25%">universe-review.cah4>Figure 10-16a Circadian Cycle universe-review.caa href="I10-67-circadianclock.jpg">[view large image]universe-review.ca/a>universe-review.ca/h4>universe-review.ca/td>
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universe-review.cath>Celestial Movementuniverse-review.ca/th>
universe-review.cath>Length of Cycleuniverse-review.ca/th>
universe-review.cath>Nameuniverse-review.ca/th>
universe-review.cath>Chronobiological Nameuniverse-review.ca/th>
universe-review.cath>Exampleuniverse-review.ca/th>
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universe-review.catd align="center">Earth's Rotationuniverse-review.ca/td>
universe-review.catd align="center">12.4 hoursuniverse-review.ca/td>
universe-review.catd align="center">tidaluniverse-review.ca/td>
universe-review.catd align="center">CIRCA TIDALuniverse-review.ca/td>
universe-review.catd align="center">mollusc feedinguniverse-review.ca/td>
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universe-review.catd align="center">Earth's Rotationuniverse-review.ca/td>
universe-review.catd align="center">24 hoursuniverse-review.ca/td>
universe-review.catd align="center">dailyuniverse-review.ca/td>
universe-review.catd align="center">CIRCADIANuniverse-review.ca/td>
universe-review.catd align="center">sleep-wake cycleuniverse-review.ca/td>
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universe-review.catd align="center">Moon's Revolutionuniverse-review.ca/td>
universe-review.catd align="center">29 daysuniverse-review.ca/td>
universe-review.catd align="center">monthlyuniverse-review.ca/td>
universe-review.catd align="center">CIRCA LUNARuniverse-review.ca/td>
universe-review.catd align="center">menstrual cycleuniverse-review.ca/td>
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universe-review.catd align="center">Earth's Revolutionuniverse-review.ca/td>
universe-review.catd align="center">365 daysuniverse-review.ca/td>
universe-review.catd align="center">yearlyuniverse-review.ca/td>
universe-review.catd align="center">CIRCANNUALuniverse-review.ca/td>
universe-review.catd align="center">rutting in deeruniverse-review.ca/td>
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universe-review.cah4 align="center">Table 10-02 Types of Biological Rhythmsuniverse-review.ca/h4>
Studies on fish, duck, bat and sparrow showed that they all exhibit circadian rhythmicity even when they are blind or are kept in cold temperature constantly. The pineal gland had been identified as the internal clock. It secretes a hormone called melatonin, which induces drowsiness and is mostly produced at night. It is sold in Health Food stores to treat insomnia in the elderly. The universe-review.caa href="universe-review.ca#pineal/default.htm#pineal/">pineal glanduniverse-review.ca/a> is sometimes called the third eye because it seems to be able to sense light (without seeing). In mammals the clock is located in two clusters of 10000 nerve cells called the universe-review.caa href="I10-59-suprac.jpg">suprachiasmatic nucleiuniverse-review.ca/a> (SCN), which are linked
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to the pineal gland. Figure 10-16b shows the mechanism of the circadian clock in the brain. The ganglion cells in the retina of the eye operate independently of the rods and cones, which mediate vision. They track fluctuations in light but are far less responsive to sudden changes or low intensity. That sluggishness befits a circadian system. It would be no good if watching fireworks or going to a movie tripped the mechanism. These cells send information about brightness and duration to the SCN, which then dispatches the information to the parts of the brain and body that control circadian processes. In response to daylight, the SCN emits signals (red arrow) that stop another brain region - the paraventricular nucleus - from producing a message that would ultimately result in melatonin's release by the pineal gland. After dark, however, the SCN releases the brake,
universe-review.catr>universe-review.catd width="25%">universe-review.cah4>Figure 10-16b Circadian Clock universe-review.caa href="I10-67-circadianclock.jpg">[view large image]universe-review.ca/a>universe-review.ca/h4>universe-review.ca/td>
universe-review.catd width="75%">allowing the paraventricular nucleus to relay a "secrete melatonin" signal (green arrows) through neurons in the upper spine and the neck to the pineal gland.universe-review.cabr />universe-review.cabr />
universe-review.ca/td>universe-review.ca/tr>universe-review.ca/table>
It is now known that there is an internal-clock mechanism working at the molecular level. Interaction of four regulatory proteins, entrained by light (the reset can be at most six hours), creates the daily rhythm of a wide range of organisms, from fungi to fruit flies to mammals.
universe-review.caol>This cellular clock mechanism is illustrated in Figure 10-17a, and is further described in the followings:universe-review.cabr />universe-review.cabr />
universe-review.cali>The cycle begins in the cell nucleus, where special initiator genes are in the "on" position (the default).universe-review.ca/li>
universe-review.cali>The initiator genes produce the proteins "CYCLE" and "CLOCK". They form a complex and bind to the E-box in the DNA coding the PER and TIM proteins.universe-review.ca/li>
universe-review.cali>mRNAs for the proteins "PER" and "TIM" are transcribed.universe-review.ca/li>
universe-review.cali>The mRNAs move out to the cytoplasm and start to make the "PER" and "TIM" proteins.universe-review.ca/li>
universe-review.cali>The "TIM" protein is light sensitive and so during the day its levels are low. This has important implications because it means "PER" can't accumulate either. It is because another clock gene called Double Time produces a protein called DBT, which acts as a protein kinase (an enzyme that removes a phosphate group from ATP). This kinase molecules makes "PER" unstable. Therefore, "PER" can only accumulate in the presence of "TIM" when the two can form the PER/TIM complex which DBT can't destabilise.universe-review.ca/li>
universe-review.cali>When the PER and TIM proteins reach a certain concentration in the cytoplasm as day turning to night, they begin to bond in pairs. These PER/TIM complexes have a shape that allows them to enter the nucleus.universe-review.ca/li>
universe-review.cali>Once inside the nucleus, the PER/TIM complexes block the operation of the initiator genes so they can no longer activate the clock genes that generate these very proteins in the first place. The clock genes switch off, and the whole process comes to a halt.universe-review.ca/li>
universe-review.cali>The PER/TIM complexes gradually dissipate from the nucleus, probably eliminated by an enzyme as night turning to day. Once the complexes have vanished, they no longer block the initiator genes, which then switch the clock genes back on, allowing the cycle to start anew. Figure 10-17b shows the timing of the events in 24 hours cycle.universe-review.ca/li>
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In the mid-1990s, it is found that these clock genes are expressed throughout the whole body, in every tissue. However, they run in different phase. For example, their expression peaked in the heart at different hours than in the liver. Circadian rhythms
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take days and sometimes weeks to adjust to a sudden shift in day length or time zone. A new schedule of light will slowly reset the SCN clock. But the other clocks may not follow its lead. The body is not only lagging; it is lagging at a dozen different places and hence the phenomenon of "jet lag", which doesn't last, presumably because all of those different drummers eventually sync up again. Seasonal
universe-review.catr>universe-review.catd width="20%">universe-review.cah4>Figure 10-17a Clock Mechanism universe-review.caa href="I10-58-clock1.jpg">[view large image]universe-review.ca/a>universe-review.ca/h4>universe-review.ca/td>
universe-review.catd width="20%">universe-review.cah4>Figure 10-17b Biological Clock universe-review.caa href="I10-58-clock2.jpg">[view large image]universe-review.ca/a>universe-review.ca/h4>universe-review.ca/td>
universe-review.catd width="60%">rhythms in many animals such as hibernation, migration, molting and mating may also be regulated by the circadian clock, which is equipped to keep track of the length of days and nights.
universe-review.ca/td>universe-review.ca/tr>universe-review.ca/table>
universe-review.cabr />universe-review.caa name="expiry">universe-review.ca/a>Recent research in 2003 points to another biological clock, which determines the life span of an organism. It is found that although the universe-review.caa href="I11-32-yeast.jpg">yeastuniverse-review.ca/a> cell normally goes through about 30 cell divisions in its five-day life span, DNA errors in daughter cells started appearing 100 times faster than normal after about 25 cell divisions - the equivalent of middle age in humans. It is noticed that about 80 percent of cancers are diagnosed in people over 55. Since both yeasts and humans use similar mechanism for copying DNA, so the rapid accrual of mutations after midlife is probably not coincidental. It could have something to do with an accumulation of damaged proteins within the cell or with breakdown in the proteins that control DNA replication and repair or with damage in the DNA itself - there is no definite answer at this point. But there seems to be a powerful force in all cells that operates on its own clock with a predetermined expiration date (see also universe-review.caa href="F11-monocell.htm#telomeres">telomeresuniverse-review.ca/a>). universe-review.cabr />universe-review.cabr />
Another recent research on ageing has identified a gene in the roundworm called daf-2. When this one gene is mutated (its function destroyed), the life span of the organism is doubled. This daf-2 gene can be considered a "master gene" of aging. This is because its protein can control the activities of many other genes. Its expression gradually shuts down the cellular repair mechanism as we aged. Cellular damages are inevitable; all multicelluar organisms eventually succumb to the exposure of chemicals, pathogen, extreme temperature and UV radiation because of the crumbling repair mechanism.
universe-review.caa href="default.htm#top/">universe-review.cah4>[Top]universe-review.ca/h4>universe-review.ca/a>
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universe-review.cah3 align="center">universe-review.caa name="brain">The Brainuniverse-review.ca/a>universe-review.ca/h3>
Brains exist because the distribution of resources necessary for survival and the hazards that threaten survival vary in space and time. There would be little need for a nervous system in an immobile organism or an organism that lived in regular and predictable environment. Brains are informed by the senses about the presence of resources and hazards; they evaluate and store this input and generate adaptive responses executed by the muscles.universe-review.cabr />
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universe-review.catd width="30%">universe-review.caa href="I10-42-gradient.jpg">universe-review.caimg src="I10-42-gradient.jpg" name="Chemical Gradient" alt="Chemical Gradient" align="left" width="300"/>universe-review.ca/a>universe-review.ca/td>
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Some of the most basic features of brains can be found in bacteria because even the simplest motile organisms must solve the problem of locating resources and avoiding toxins. They sense their environment through a large number of receptors, which are protein molecules embedded in the cell wall. The action taken in response to the inputs usually depends on the gradient of the chemicals (see Figure 10-18). Thus memory is required to compare the inputs from different locations. The strength of the signal is modulated by immediate past experience. This in turn regulates the strength of the signal sent by chemical messengers from
universe-review.ca/td>universe-review.ca/tr>
universe-review.catr>universe-review.catd width="30%">universe-review.cah4>Figure 10-18 E. coli's Response to Chemical Gradient universe-review.caa href="I10-42-gradient.jpg">[view large image]universe-review.ca/a>universe-review.ca/h4>universe-review.ca/td>
universe-review.catd width="70%">the receptor to the flagellar motors. Thus even at the unicellular level, the bacteria have already possessed the ability to integrate numerous analog inputs and generate a binary (digital) output of stop or go.
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In multicellur organism cells specialized for receptor function are located on the surface. Other cells specialized for the transmission and analysis of information are located in the protected interior and are linked to effector cells, usually muscles, which produce adaptive responses. As do unicellular organisms, neurons integrate the diverse array of incoming information from the receptors, which in neurons may result in the firing of an action potential rather than swimming toward a nutrient source as in the unicellular organisms.
universe-review.ca/td>universe-review.ca/tr>
universe-review.catr>universe-review.catd width="30%">universe-review.cah4>Figure 10-19 Neuron universe-review.caa href="I10-40-nerve.jpg">[view large image]universe-review.ca/a>universe-review.ca/h4>universe-review.ca/td>
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universe-review.ca/td>universe-review.ca/tr>universe-review.ca/table>
universe-review.caA NAME="neurons">universe-review.ca/A>Neurons have a characteristic architecture (see Figure 10-19) in which the chemical receptors tend to be located on branching structures, the universe-review.caA NAME="dendrites">universe-review.ca/A>dendrites, which extend from the cell body. The dendrites increase the receptive surface of the neurons, but their length is constrained by their electrical properties so that they rarely extend more than a few millimeters from the cell body. They require a great deal of energy to maintain the ionic balance between themselves and their surrounding fluids, which is constantly in flux as a result of the opening and closing of channels through the neuronal membranes.universe-review.cabr />universe-review.cabr />
Neurons are dynamically polarized, so that information flows from the fine dendrites into the main dendrites and then to the cell body, where it is converted into all-or-none signals, the action potentials, which are relayed to other neurons by the universe-review.caA NAME="axon">universe-review.ca/A>axon, a long wirelike structure. The action potential is initiated by the opening of voltage-sensitive sodium channels in the membrane of the axon at the point where the axon emerges from the cell body. Sodium ions rush into the neurons from the extracellular fluid, resulting in a transient change in the voltage difference between the neuron and the surrounding environment. The action potential travels like a wave from the cell body down the axon. The action potential enables the neuron to communicate rapidly with other neurons over sizable distances, sometime more than a meter away. When the action potential reaches an axon terminal (the synapse), it causes the terminals to secrete a chemical messenger (neurotransmitter), generally an amino acid or its derivative, which binds to receptors in the post-synaptic neurons on the far side of the synaptic cleft. When the postsynaptic potential has reached a specific value an action potential is triggered and the signal is passed to the next neuron.universe-review.cabr />universe-review.cabr />
Action potentials and voltage-gated sodium channels are present in jellyfish, which are the simplest organisms to possess nervous systems. The development of this basic neuronal mechanism set the stage for the proliferation of animal life that occurred during the Cambrian period. Among these Cambrian animals were the early chordates, which possessed very simple brains. Some of these early fish developed a unique way to insulate their axons by wrapping them with a fatty material called myelin, which greatly facilitated axonal transmission and evolution of larger brains. Some of their descendants, which also were small predators, crawled up on the muddy shores and eventually took up permanent residence on dry land. Challenged by the severe temperature changes in the terrestrial environment, some experimented with becoming warm-blooded, and the most successful became the ancestors of birds and mammals. Changes in the brain and parental care were a crucial part of the set of mechanisms that enabled these animals to maintain a constant body temperature. universe-review.cabr />universe-review.cabr />
Animals with large brains are rare -- there are tremendous costs associated with large brains (the active human brain consumes about 20 watts). The brain must compete with other organs in the body for the limited amount of energy available, which is a powerful constraint on the evolution of large brains. Large brains also require a long time to mature, which greatly reduces the rate at which their possessors can reproduce. Because large-brained infants are slow to develop and are dependent on their parents for such a long time, the parents must invest a great deal of effort in raising their infants.
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universe-review.catd width="20%">universe-review.caa href="R10-10-brain.htm">universe-review.caimg src="I10-39-brain1.jpg" name="Brain 1" alt="Brain 1" align="left" width="125"/>universe-review.ca/a>universe-review.ca/td>
universe-review.catd width="20%">universe-review.caa href="I10-39-brain2.jpg">universe-review.caimg src="I10-39-brain2.jpg" name="Brain 2" alt="Brain 2" align="left" width="260"/>universe-review.ca/a>universe-review.ca/td>
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Young reptiles function as miniature versions of adults, but baby mammals and birds are dependent because of their poor capacity to thermo-regulate, the consequence of their need to devote most their energy to growth. Most mammals solve the problem with universe-review.caa href="I10-39-care.jpg">maternal careuniverse-review.ca/a>, shelter, warmth, and milk. In most birds, both parents cooperate to provide food and shelter to their young. The expanded forebrain and parental care provide mechanisms for the extra-genetic transmission of information from one generation to the next. This transmission results from the close contact with parents during infancy, which provides
universe-review.ca/td>universe-review.ca/tr>
universe-review.catr>universe-review.catd width="20%">universe-review.cah4>Figure 10-20a Human Brain universe-review.ca/h4>universe-review.ca/td>
universe-review.catd width="20%">universe-review.cah4>Figure 10-20b Human Brain universe-review.cabr />[view large imageuniverse-review.caa href="R10-10-brain.htm"> auniverse-review.ca/a>,universe-review.caa href="I10-39-brain2.jpg"> buniverse-review.ca/a>]universe-review.ca/h4>universe-review.ca/td>
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the young with opportunity to observe and learn from their behavior; the expanded forebrain provides an enhanced capacity to store these memories. The expanded forebrain and the observation of parents are probably necessary for the establishment of successful care giving behavior itself, as the young mature into adults that will in their turn have to serve dependent young. During the period of infant dependency, baby mammals and birds play, behavior that may be essential for the development of the forebrain. The baby's playful interaction with its environment may serve to provide the initial training of the forebrain networks that ultimately will enable the animal to localize, identify, and capture resources in its environment.universe-review.cabr />universe-review.cabr />
The human brain can be divided into three parts: the hindbrain, which has been inherited from the reptiles; the limbic system, which was first emerged in mammals; and the forebrain, which has its full development in human. Different views of the human brain are shown in Figure 10-20a and 10-20b. Tables 10-02 lists the functions of the different parts of the human brain. The brain is separated into two hemispheres. Apart from a single little organ -- the pineal gland in the centre base of the brain -- every brain module is duplicated in each hemisphere. The left brain is calculating, communicative and capable of conceiving and executing complicated plans -- the reductionistic brain; while the right one is considered as gentle, emotional and more at one with the natural world -- the holistic brain. The universe-review.caa href="I10-80-forebrain1.jpg">cerebral cortexuniverse-review.ca/a> is covered in a thin skin of deeply wrinkled grey tissue called the grey matter (densely packed neurons for information processing). Each infold on the surface is known as a sulcus, and each bulge is know as a gyrus. While the white tissue inside are axons -- tentacles which reach out to other cells (to relay information). The cortex can be broken down into many functional regions, each containing thousands of cortical columns (oriented perpendicular to the cortical surface). Columns are typically about half a millimeter in diameter and contain about one hundred thousand neurons. They are the units of cognition (the mental process of acquiring knowledge by the use of reasoning, intuition or perception).
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universe-review.catable bgcolor="EBFBFB" border="1" width="100%" align="center">
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universe-review.cath>Structureuniverse-review.ca/th>
universe-review.cath>Locationuniverse-review.ca/th>
universe-review.cath>Functionsuniverse-review.ca/th>
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universe-review.catd align="center">universe-review.caa href="I10-80-hindbrain1.jpg">Hindbrainuniverse-review.ca/a> universe-review.cabr />(universe-review.caa href="I10-64-brain.jpg">Reptilian Brainuniverse-review.ca/a>)universe-review.ca/td>
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universe-review.catd align="center">universe-review.caa href="I10-80-hindbrain2.jpg">Medullauniverse-review.ca/a>universe-review.ca/td>
universe-review.catd align="center">at the top of the spinal corduniverse-review.ca/td>
universe-review.catd align="center">controls breathing, heart rate, and blood pressure.universe-review.ca/td>
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universe-review.catr>
universe-review.catd align="center">universe-review.caa href="I10-80-hindbrain2b.jpg">Ponsuniverse-review.ca/a>universe-review.ca/td>
universe-review.catd align="center">above the medullauniverse-review.ca/td>
universe-review.catd align="center">regulates sensory information and facial expressions.universe-review.ca/td>
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universe-review.catd align="center">universe-review.caa href="I10-80-hindbrain2a.jpg">Cerebellumuniverse-review.ca/a>universe-review.ca/td>
universe-review.catd align="center">at the lower rearuniverse-review.ca/td>
universe-review.catd align="center">controls movement, coordination, balance, muscle tone, and learning motor skills.universe-review.ca/td>
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universe-review.catd align="center">universe-review.caa href="I10-80-reticular.jpg">Reticular Formationuniverse-review.ca/a>universe-review.ca/td>
universe-review.catd align="center">a network of nerves extends from the medulla to the cerebrumuniverse-review.ca/td>
universe-review.catd align="center">monitors the general level of activity in the hindbrain and maintains a state of arousal; essential for the regulation of sleep and wakefulness.universe-review.ca/td>
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universe-review.catd align="center">universe-review.caa href="I10-80-midbrain.jpg">Midbrain (superior & inferior colliculus)universe-review.ca/a>universe-review.ca/td>
universe-review.catd align="center">above the pons between the hindbrain and forebrainuniverse-review.ca/td>
universe-review.catd align="center">relays sensory information from the spinal cord to the forebrain.universe-review.ca/td>
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universe-review.catd align="center">universe-review.caa href="I10-41-limbic.jpg">Limbic Systemuniverse-review.ca/a> universe-review.cabr />(universe-review.caa href="I10-64-brain.jpg">Mammalian Brainuniverse-review.ca/a>)universe-review.ca/td>
universe-review.catd align="center">at the center of the brainuniverse-review.ca/td>
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universe-review.catd align="center">universe-review.caa href="I10-80-limbic1.jpg">Thalamusuniverse-review.ca/a>universe-review.ca/td>
universe-review.catd align="center">in the middle of the limbic systemuniverse-review.ca/td>
universe-review.catd align="center">relays incoming information (except smell) to the appropriate part of the brain for further processing.universe-review.ca/td>
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universe-review.catd align="center">universe-review.caa href="I10-80-nuclei.jpg">Hypothalamus, Pituitary Glanduniverse-review.ca/a>universe-review.ca/td>
universe-review.catd align="center">beneath thalamusuniverse-review.ca/td>
universe-review.catd align="center">regulates basic biological drives, hormonal levels, sexual behavior, and controls autonomic functions such as hunger, thirst, and body temperature.universe-review.ca/td>
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universe-review.catd align="center">universe-review.caa href="I10-80-optic.jpg">Optic Chiasmuniverse-review.ca/a>universe-review.ca/td>
universe-review.catd align="center">in front of the pituitary glanduniverse-review.ca/td>
universe-review.catd align="center">left-right optic nerves cross-over point.universe-review.ca/td>
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universe-review.catd align="center">universe-review.caa href="I10-80-septum.jpg">Septumuniverse-review.ca/a>universe-review.ca/td>
universe-review.catd align="center">adjacent to hypothalamusuniverse-review.ca/td>
universe-review.catd align="center">stimulates sexual pleasureuniverse-review.ca/td>
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universe-review.catd align="center">universe-review.caa href="I10-80-limbic1a.jpg">Hippocampusuniverse-review.ca/a>universe-review.ca/td>
universe-review.catd align="center">at the bottom of the limbic systemuniverse-review.ca/td>
universe-review.catd align="center">mediates learning and memory formation.universe-review.ca/td>
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universe-review.catd align="center">universe-review.caa href="I10-80-limbic1b.jpg">Amygdalauniverse-review.ca/a>universe-review.ca/td>
universe-review.catd align="center">in front of the hippocampusuniverse-review.ca/td>
universe-review.catd align="center">responsible for anxiety, emotion, and fearuniverse-review.ca/td>
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universe-review.catd align="center">universe-review.caa href="I10-80-limbic2.jpg">Mammillary Body, Fornixuniverse-review.ca/a>universe-review.ca/td>
universe-review.catd align="center">linked to the hippocampusuniverse-review.ca/td>
universe-review.catd align="center">have a role in emotional behavior, learning, and motivation.universe-review.ca/td>
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universe-review.catd align="center">universe-review.caa name="pineal">universe-review.ca/a>universe-review.caa href="I10-80-pineal.jpg">Pineal Glanduniverse-review.ca/a>universe-review.ca/td>
universe-review.catd align="center">at centre of the limbic system (the third eye for fishes and amphibians)universe-review.ca/td>
universe-review.catd align="center">involves in circadian and circannual rhythms; possibly involves in maturation of sex organs.universe-review.ca/td>
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universe-review.catd align="center">universe-review.caa href="I10-80-limbic2.jpg">Caudate Nucleus, Putamen, Globus Pallidusuniverse-review.ca/a>, universe-review.caa href="I10-80-basal.jpg">Basal Gangliauniverse-review.ca/a> (Striatum)universe-review.ca/td>
universe-review.catd align="center">outside the thalamusuniverse-review.ca/td>
universe-review.catd align="center">involves in movement, emotions, planning and in integrating sensory informationuniverse-review.ca/td>
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universe-review.catd align="center">universe-review.caa href="I10-80-ventricles.jpg">Ventricles and Central Canaluniverse-review.ca/a>universe-review.ca/td>
universe-review.catd align="center">from tiny central canal within the spinal cord to the enlarged hollows within the skull called ventriclesuniverse-review.ca/td>
universe-review.catd align="center">fills with cerebrospinal fluid for mechanical protection.universe-review.ca/td>
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universe-review.catd align="center">universe-review.caa href="I10-80-cingulate.jpg">Cingulate Gyrusuniverse-review.ca/a>universe-review.ca/td>
universe-review.catd align="center">above corpus callosumuniverse-review.ca/td>
universe-review.catd align="center">concentrates attention on adverse internal stimuli such as pain, contains the feeling of self.universe-review.ca/td>
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universe-review.catd align="center">universe-review.caa href="I10-80-corpus.jpg">Corpus Callosumuniverse-review.ca/a>universe-review.ca/td>
universe-review.catd align="center">under the cingulate gyrusuniverse-review.ca/td>
universe-review.catd align="center">is a bundle of nerve fibers linking the cerebral hemispheres, involve in language learning.universe-review.ca/td>
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universe-review.catd align="center">universe-review.caa href="I10-80-forebrain1.jpg">Forebrainuniverse-review.ca/a> universe-review.cabr />(universe-review.caa href="I10-64-brain.jpg">Human Brainuniverse-review.ca/a>)universe-review.ca/td>
universe-review.catd align="center">universe-review.ca/td>
universe-review.catd align="center">universe-review.ca/td>
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universe-review.catd align="center">universe-review.caa href="I10-80-forebrain2.jpg">Frontal Lobeuniverse-review.ca/a> universe-review.cabr />(Conscious Brain)universe-review.ca/td>
universe-review.catd align="center">in front of the headuniverse-review.ca/td>
universe-review.catd align="center">controls voluntary movement, thinking, and feeling.universe-review.ca/td>
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universe-review.catd align="center">universe-review.caa href="I10-80-prefrontal.jpg">Prefrontal Cortexuniverse-review.ca/a>universe-review.ca/td>
universe-review.catd align="center">in front of the frontal lobeuniverse-review.ca/td>
universe-review.catd align="center">inhibits inappropriate actions, forms plans and concepts, helps focus attention, and bestows meaning to perceptions.universe-review.ca/td>
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universe-review.catd align="center">universe-review.caa href="I10-80-forebrain2c.jpg">Parietal Lobeuniverse-review.ca/a>universe-review.ca/td>
universe-review.catd align="center">in top rear of the headuniverse-review.ca/td>
universe-review.catd align="center">contains the primary somatosensory area that manages skin sensation.universe-review.ca/td>
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universe-review.catd align="center">universe-review.caa href="I10-80-forebrain2a.jpg">Occipital Lobeuniverse-review.ca/a>universe-review.ca/td>
universe-review.catd align="center">in the back of the headuniverse-review.ca/td>
universe-review.catd align="center">contains the visual cortex to manage vision.universe-review.ca/td>
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universe-review.catd align="center">universe-review.caa href="I10-80-forebrain2b.jpg">Temporal Lobeuniverse-review.ca/a>universe-review.ca/td>
universe-review.catd align="center">on each side of the head above the templesuniverse-review.ca/td>
universe-review.catd align="center">contains the auditory cortex to manage hearing and speech.universe-review.ca/td>
universe-review.ca/tr>universe-review.ca/table>
universe-review.cah4 align="center">Table 10-03 Human Brain universe-review.ca/h4>
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universe-review.catd width="20%">universe-review.caa href="I10-47-waves.jpg">universe-review.caimg src="I10-47-waves.jpg" name="Brain Waves" alt="Brain Waves" align="left" width="200"/>universe-review.ca/a>universe-review.ca/td>
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universe-review.caA NAME="waves">universe-review.ca/A>It is well known that the brain is an electrochemical organ; a fully functioning brain can generate as much as 20 watts of electrical power. Even though this electrical power is very limited, it does occur in very specific ways that are characteristic of the human brain. Electrical activity emanating from the brain can be displayed in the form of brainwaves. There are four categories of these brainwaves, ranging from the most active to the least active. Figure 10-21 is produced by an universe-review.caa href="I10-63-EEG.jpg">EEGuniverse-review.ca/a> (ElectroEncephaloGraph) chart recorder to show the different kind of brainwave according to the different state of the brain. These are all oscillating electrical voltages in the brain, but they are very tiny voltages, just a few millionths of a volt. Electrodes are placed on the outer surface of the head to detect electrical changes in the extracellular fluid of the brain in response to changes in potential
universe-review.ca/td>universe-review.ca/tr>
universe-review.catr>universe-review.catd width="20%">universe-review.cah4>Figure 10-21 Brain Waves universe-review.caa href="I10-47-waves.jpg">[view large image]universe-review.ca/a>universe-review.ca/h4>universe-review.ca/td>
universe-review.catd width="75%">among large groups of neurons. The resulting signals from the electrodes are amplified and recorded.universe-review.cabr />universe-review.cabr />universe-review.ca/td>
universe-review.ca/tr>universe-review.ca/table>
Brain waves originate from the cerebral cortex, but also reflect activities in other parts of the brain that influence the cortex, such as the reticular formation. Because the intensity of electrical changes is directly related to the degree of neuronal activity, brain waves vary markedly in amplitude and frequency between sleep and wakefulness. Beta wave rhythms appear to be involved in higher mental activity, including perception and consciousness. It seems to be associated with consciousness, e.g., it disappears with general anesthesia. Other waves that can be detected are Alpha, Theta, and Delta. When the hemispheres or regions of the brain are producing a wave synchronously, they are said to be coherent. Alpha waves are generated in the Thalamus (the brain within the brain), while Theta waves occur mainly in the parietal and temporal regions of the cerebrum. The Alpha and Theta waves seem to be associated with creative, insightful thought. When an artist or scientist has the "aha" experience, there's a good chance he or she is in Alpha or Theta. These two kinds of brain waves are also associated with relaxation and, stronger immune systems. Therefore, many people try to train themselves to enter such states through various biofeedbackuniverse-review.casup>universe-review.caa href="universe-review.ca#seven/default.htm#seven/">7universe-review.ca/a>universe-review.ca/sup> techniques (with varying degree of success). Delta Waves occur during sleep. They originate from the cerebral cortex when it is not being activated by the reticular formation. In slow-wave sleep, the entire brain oscillates in a gentle rhythm quite unlike the fragmented oscillations of normal consciousness.
universe-review.caa href="default.htm#top/">universe-review.cah4>[Top]universe-review.ca/h4>universe-review.ca/a>
universe-review.cahr align="center" width="15%" />
universe-review.cah3 align="center">universe-review.caa name="sleep">Sleep and universe-review.caa name="dream">universe-review.ca/a>Dreamuniverse-review.ca/a>universe-review.ca/h3>
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universe-review.catd width="20%">universe-review.caa href="I10-47-sleep.jpg">universe-review.caimg src="I10-47-sleep.jpg" name="Sleep" alt="Sleep" align="left" width="200"/>universe-review.ca/a>universe-review.ca/td>
universe-review.catd width="20%">universe-review.caa href="I10-47-dream1.jpg">universe-review.caimg src="I10-47-dream1.jpg" name="Dream, Tonic" alt="Dream, Tonic" align="left" width="200"/>universe-review.ca/a>universe-review.ca/td>
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Sleep is another process in the brain that we still have much to learn. We know that while we sleep, we cycle between two very different states. The first is called slow wave sleep characterized by long waves of undulating electrical activity (Figure 10-21). The second is rapid eye movement (REM) sleep characterized by frantic brain activity that looks very much like wakefulness. It also has very obvious physical signs: the
universe-review.ca/td>universe-review.ca/tr>
universe-review.catr>universe-review.catd width="20%">universe-review.cah4>Figure 10-22 Dreaming Brain universe-review.cabr />universe-review.caa href="I10-47-sleep.jpg">[view large image]universe-review.ca/a>universe-review.ca/h4>universe-review.ca/td>
universe-review.catd width="20%">universe-review.cah4>Figure 10-23a Peaceful Dream universe-review.caa href="I10-47-dream1.jpg">[view large image]universe-review.ca/a>universe-review.ca/h4>universe-review.ca/td>
universe-review.catd width="60%">rapid flickering motion of the eyeballs, the near-total muscle paralysis (to prevent from acting out the dreams), and penile erections. universe-review.ca/td>universe-review.ca/tr>universe-review.ca/table>
universe-review.cap>It is found that dreams are associated with REM sleep. During dreaming, the visual cortex is very active (to generate internal imagery), as are the amygdala, thalamus and the brainstem, which fits with the fact that dreams tend to be very visual and emotional. At the same time, the prefrontal and parietal cortices and the posterior cingulate, areas which deal with rational thought and attention, are all very quiet, which tallies with the lack of insight, illogicality and time distortion that characterizes dreams. Although the hippocampus is actively processing long-term memory, the short-term memory region is inactive, which explains why dreamer forgets what just happened (see Figure 10-22).universe-review.ca/p>
It is now known that REM sleep falls into two types, generating two different kinds of dreams. Firstly there is the tonic component. It is accompanied by muscle relaxation and sometimes sexual arousal. Tonic REM takes place earlier on in the sleeping cycle. It is calmer, more restful, and more passive. When woken, the dreamer typically reports such things as "I was
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universe-review.catd width="20%">universe-review.caa href="I10-47-dream2.jpg">universe-review.caimg src="I10-47-dream2.jpg" name="Dream, Phasic" alt="Dream, Phasic" align="left" width="240"/>universe-review.ca/a>universe-review.ca/td>
universe-review.catd width="20%">universe-review.caa href="I10-47-dream3.jpg">universe-review.caimg src="I10-47-dream3.jpg" name="Dream, Data Processing" alt="Dream, Data Processing" align="left" width="200"/>universe-review.ca/a>universe-review.ca/td>
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feeling floaty" (Figure 23a) or "there was a feeling of peace". The second type of REM sleep is known as phasic and is characterized by jerky eye movements, spasmodic limb and facial twitching and sudden breathing changes. When volunteers are woken from this sort of REM sleep, they typically describe their dreams as being strongly visual, active and "real". Phasic REM and its accompanying dreams tend to occur later on in the sleeping period. Nightmares are associated with this type of sleep (Figure 23b).
universe-review.ca/td>universe-review.ca/tr>
universe-review.catr>universe-review.catd width="20%">universe-review.cah4>Figure 10-23b Nightmare universe-review.cabr />universe-review.caa href="I10-47-dream2.jpg">[view large image]universe-review.ca/a>universe-review.ca/h4>universe-review.ca/td>
universe-review.catd width="20%">universe-review.cah4>Figure 10-23c Data Processing universe-review.cabr />universe-review.caa href="I10-47-dream3.jpg">[view large image]universe-review.ca/a>universe-review.ca/h4>universe-review.ca/td>
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universe-review.ca/tr>universe-review.ca/table>
universe-review.cap>REM sleep appears to have arisen quite early in evolution - reptiles, birds and mammals all do it. Therefore, it must serve a very useful function. There are many theories of sleep function, which fall into four broad classes: restoration and recovery, predator avoidance, energy conservation and information relocation from short-term to long-term memory (discarding redundant data in the process) similar to the transfer of data from disk to tape in the IT (information technology) industry (Figure 23c). But not one of them has been confirmed or refuted. universe-review.ca/p>
universe-review.cap>Recent research in 2003 indicates that non-REM sleep may give brain cells a chance to repair themselves, and REM sleep may allow the brain's neuron receptors to recover (regain full sensitivity). It is found that Animals born inmature require more REM sleep. Thus REM sleep may also act as a substitute for the external stimulation that prompts neuronal development in creatures that are mature at brith. Sleep research will identify the brain regions that control REM and non-REM sleep. It will lead to a more comprehensive and satisfying understanding of sleep, its functions, the mechanisms and evolution. It will probably gain insights into exactly what is repaired and rested, why these processes are best done in sleep.universe-review.ca/p>
universe-review.caa href="default.htm#top/">universe-review.cah4>[Top]universe-review.ca/h4>universe-review.ca/a>
universe-review.cahr align="center" width="15%" />
universe-review.cah3 align="center">universe-review.caa name="meditation">Meditationuniverse-review.ca/a>universe-review.ca/h3>
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Even though the pre-frontal and parietal lobes are inactivated during both REM sleep (see Figure 10-22) and meditation (see Figure 10-24), meditation is different from sleeping or dreaming. It generates brainwaves in the Theta state, which is in a slightly higher frequency range than the Delta (sleeping) state (see Figure 10-21). The state is on the border line between consciousness and sleeping. The anterior cingulate gyrus becomes underactive in meditation (see Figure 10-25). As shown in Table 10-03, the cingulate gyrus concentrates on internal stimuli, and contains the feeling of self. Curiously, this is the same area that becomes underactive in hypnosis (when the identity of self dissolved) and universe-review.caa href="I10-62-schizophrenia.jpg">Schizophreniauniverse-review.ca/a> (when own thoughts are confused with outside voices).
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universe-review.catd width="20%">universe-review.cah4>Figure 10-24 Meditation universe-review.cabr />universe-review.caa href="R10-15-meditation.htm">[view large image]universe-review.ca/a>universe-review.ca/h4>universe-review.ca/td>
universe-review.catd width="20%">universe-review.cah4>Figure 10-25 Meditating Brain universe-review.cabr />universe-review.caa href="I10-49-meditating2.jpg">[view large image]universe-review.ca/a>universe-review.ca/h4>universe-review.ca/td>
universe-review.catd width="60%">Thus it doesn't seem to be accidental that in meditation, the sense of boundaries is lost and it induces a feeling of "at one" (union) with the universe. universe-review.ca/td>
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The physiological effects related to meditation are measurable and reliably repeatable. It includes the lowering of a subject's metabolic rate, decreasing blood pressure, pulse rate and muscle tension. Meditation can counteract the stress-induced fight-or-flight response and achieved a calmer and more relaxing state, which tends to strengthen the immune systems. One report showed that the subject could reduce oxygen intake to 1/3 of the normal resting state by allowing the universe-review.caa href="R10-16-ANS.htm#parasympathetic">parasympathetic nervous systemuniverse-review.ca/a> to take over - an extraordinary feat, given that respiration is controlled by the universe-review.caA NAME="ANS">universe-review.ca/A>universe-review.caa href="R10-16-ANS.htm">autonomic nervous systemuniverse-review.ca/a>, over which we ordinarily have no conscious control. Other studies suggest that meditation can help to alleviate bronchial asthma, hypertension, and insomnia. It is being recommended by more and more physicians as a way to prevent, slow or at least control the pain of chronic diseases like heart conditions, AIDS, cancer and infertility. It is now believed that the body produces more nitric oxide when deeply relaxed, and that this molecule acts as an antidote to cortisol (hormone associated with inflammation) and other potentially toxic stress hormones.
universe-review.cap>Meditation, nearly as old as humanity, has always been part of Eastern religions. Starting from 2nd century A.D. meditation became important part of Christian practice until early 1500s when Martin Luther disapproved mysticism. Jewish and Muslim meditations have established around 1000 A.D. Meditation was used as a medium to communicate with the higher being(s). Actually, the brain is playing trick on the practitioners by producing various illusions. Now the West is rediscovering the benefits of meditation. In its most modern forms, it has dropped the mantra bit that has the subject memorize a secret phrase or syllable; instead it only requires focusing on a sound or breathing. In fact, just closing the eyes in a quiet place (to block sensory inputs) and relaxing the mind (to minimize internal processing) would attain the same result without much ado.universe-review.ca/p>
universe-review.caa href="default.htm#top/">universe-review.cah4>[Top]universe-review.ca/h4>universe-review.ca/a>
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universe-review.cah3 align="center">universe-review.caa name="consciousness">Consciousnessuniverse-review.ca/a>universe-review.ca/h3>
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Consciousness is usually defined as the part of the human minduniverse-review.casup>universe-review.caa href="universe-review.ca#eight/default.htm#eight/">8universe-review.ca/a>universe-review.ca/sup> that is aware of the feeling, thoughts and surroundings. Actually there is no simple, agreed-upon definition of consciousness. A more detailed definition(s) will be discussed later. Most of the philosophical discussions of consciousness arose from the mind-body issues posed by Rene' Descartes in the 17th century. He asked: Is the mind, or consciousness, independent of matter? Is consciousness physical or non-physical? It is now recognized that the phenomena by which we define consciousness are correlated with certain configurations of activity in certain nervous systems and not with others. Most neural activity doesn't generate consciousness, even in the supremely conscious human brain. Moreover, the activities that do generate consciousness do not produce it by accident or in a happenstance manner. Consciously processed events in the nervous system have a very clear physical signature, in the form of characteristic brain activity. There is good empirical evidence that consciously registered events leave distinct traces in the brain and are processed in special ways within the brain's networks. Techniques such as EEG, universe-review.caa href="R10-22-tomography.htm#MRI">f MRIuniverse-review.ca/a>, and universe-review.caa href="R10-22-tomography.htm#PET">PETuniverse-review.ca/a> provide information about the relationship between mental tasks and the collective activities of groups of many millions of
universe-review.ca/td>universe-review.ca/tr>
universe-review.catr>universe-review.catd width="25%">universe-review.cah4>Figure 10-26 Correlation of universe-review.ca/h4>universe-review.ca/td>
universe-review.catd width="75%">universe-review.cah4>Brain Activities and Mental Tasks universe-review.caa href="I10-44-MRI.jpg">[view large image]universe-review.ca/a>universe-review.ca/h4> universe-review.ca/td>
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neurons (see Figure 10-26). In stark contrast to this, electrodes have been developed which are so fine that their tips can be inserted into single cells so that the firings of individual neurons in some brain location can be monitored. It is possible to see how an individual neuron reacts when an animal is looking at an object moving sideways, or seeing the colour blue, or planning an action ...universe-review.cabr />universe-review.cabr />
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Sigmund Freud, the founder of psychoanalysis, compared the human mind to an iceberg. The tip above the water represents consciousness, and the vast region below the surface symbolizes the unconscious mind. This subconscious mind is the sum total of our past experiences. What we feel, think, or do forms the basis of our experience. These experiences are stored in the form of subtle impressions in our subconscious mind. These impressions interact with one another and create tendencies. The resultant of these tendencies determines our character (see Figure 10-27). However, if the unconsicous drives (the id) might prompt behavior that would be incompatible with our civilized conception of ourselves, the action would be suppressed by the conscious mind (the ego). This Freudian concept has been fallen out of favour by 1950s. Better understanding of brain chemistry gradually replaced his model with a biological explanation of how the mind arises from neuronal activity. But since mid 1990s, attempts to piece together diverse neurological findings have validated the general sketch Freud made almost a century ago.
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universe-review.catr>universe-review.catd width="25%">universe-review.cah4>Figure 10-27 Consciousness universe-review.caa href="I10-43-consciousness.jpg">[view large image]universe-review.ca/a>universe-review.ca/h4>universe-review.ca/td>
universe-review.catd width="75%">The lower diagram in Figure 10-27 identifies some Freudian terminologies with the modern anatomy of the human brain.universe-review.cabr />universe-review.cabr />universe-review.ca/td>
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The unconscious processing seems to be simpler than the conscious one. It includes a whole range of neural processing from the automatic reflex of some simple animals such as the E. coli in Figure 10-18 to automatic actions taken by human. Actually conscious and unconscious processing is similar; they are different versions of the same thing, presumably using at least some of the same neural equipments. The consciously performed actions of the beginner are a stumbling version of the more unconscious actions of the skilled performer. Conscious and unconscious forms blend into each other; there is no hard dividing line. Conscious processing can be summarized as the combination of unconscious processing with feeling or thought - sometimes more, sometimes less, depending on the level of detail or complexity. The brain is constantly trying to automate processes, thereby dispelling them from consciousness; in this way, its work will be completed faster, more effectively and at a lower metabolic level. Consciousness, on the other hand, is slow, subject to error and expensive.
universe-review.caul>The state of consciousness can be divided into three levels:universe-review.cabr />universe-review.cabr />
universe-review.cali>The most basis state is that of being conscious and of not being conscious. The site of consciousness seems to be in or around the thalamus, or it should at least involve interactions between the thalamic and cortical systems.universe-review.ca/li>
universe-review.cali>A background state is an over all state of consciousness such as being awake, being asleep, dreaming, being under hypnosis, and so on. It includes a range of normal and of "altered" states. universe-review.ca/li>
universe-review.cali>Specific states of consciousness are the fine-grained states of subjective experience. Such states might include the experience of a particular visual image, of a particular sound pattern, of a detailed stream of conscious thought, and so on. A detailed visual experience, for example, might include the experience of certain shapes and colors, of specific arrangements of objects, of various relative distances and depths, and so on. Much of the most interesting work on "Neural Correlates of Consciousness" (NCC) is concerned with states like these. NCC usually probes neural activity deep down into the cellular level. universe-review.ca/li>
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The three classes of consciousness definition:universe-review.cabr />universe-review.cabr />
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universe-review.cali>The first is the definition of consciousness as a state. Most mammals, and many non-mammalian species as well, have this aspect of conscious capacity. All mammals alternate between states that can be labeled as asleep, awake, and alert. Several species of mammals even seem to dream as we do and show rapid eye movements and brain waves that resemble our own during certain phases of asleep. Most mammals also show daytime variation in arousal; i.e., they alternate between what we call active, vigilant, and wide-awake states and those that are passive, unfocused, and marked by a reduced level of activity.universe-review.ca/li>universe-review.ca/ul>
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universe-review.catr>universe-review.catd width="20%">universe-review.cah4>Figure 10-28a Consciousness Circuit universe-review.caa href="R10-15-defconscious.htm">[view large image]universe-review.ca/a>universe-review.ca/h4>universe-review.ca/td>
universe-review.catd width="20%">universe-review.cah4>Figure 10-28b Thalamus Nuclei universe-review.caa href="I10-80-nuclei.jpg">[view large image]universe-review.ca/a>universe-review.ca/h4>universe-review.ca/td>
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universe-review.cali>A second class of definition takes an architectural approach, whereby consciousness is considered as the central processor located at the top of the control hierarchy. Its physical counterpart is distributed across several subsystems of anatomical structures. These subsystems are identified to be the various nuclei located in the hypothalamus (see Figure 10-28a). Figure 10-28b shows the actual location of the various hypothalamus nuclei, which are the mediator between the unconscious atuonomic functions in the brain stem and conscious awareness - the higher mental activities in the forebrain. This conceptual organization brings cognition, emotion, and action under a unified command. Consciousness would correspond to the active state of this command center in the hypothalamus. For instance, when suddenly you feel the need for a drink. This "need" is the hypothalamus, on behalf of its autonomic subsystem, breaking through into your conscious awareness and modifying your behavior to meet your body's basic needs.universe-review.cabr />universe-review.cabr />
universe-review.caul>Here's how it works:universe-review.cabr />universe-review.cabr />
universe-review.cali>Inputs arrive in the hypothalamus as nerve signals. They may be from the senses, especially sight, taste, and touch; from the limbic system or recticular formation in the brain itself (about basic need and drives); and from internal organs such as the heart and intestines. It is also influenced by hormones circulating in the blood, and by concentrations of glucose, sodium, and other substances in the blood passing through it and in the cerebrospinal fluid just above it. Inside the hypothalamus are several pairs of relatively discrete nuclei, or areas. Some tasks of the hypothalamus are assigned to a specific pair; others seem to be spread through several areas which communicate by nerve fibers so that they can work together as a single "center" for one main role.universe-review.ca/li>
universe-review.cali>The hypothalamus sends outputs as nerve signals to the motor (muscle controlling) parts of the midbrain, the limbic system, and the various autonomic centers in the brain stem that control processes such as heartbeat, blood pressure, and urine production, as well as the glands producing saliva, sweat, and digestive juices. It also produces hormones - such as the antidiuretic hormone (ADH) - which are passed to the pituitary.universe-review.ca/li>
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The late Francis Crick (1916-2004) believed that the command center is in the universe-review.caa href="I10-80-claustrum.jpg">claustrumuniverse-review.ca/a> instead of the hypothalamus. The claustrum is a thin sheet of grey matter that resides parallel to and below part of the cortex. It is present in all mammals, but it has been little studied and its function is not known. What is known, however, is that there are two-way connections between the claustrum and most, if not all, parts of the cortex as well as subcortical structures involved in emotion. It is likened to the conductor of an orchestra, who is responsible for binding the performances by individual musicians into an integrated whole that can be much more than the sum of its parts. The neuroanatomical connections of the claustrum, then, just match with the "conductor" required to bind together the various disparate components of the conscious experience represented in many different brain regions.universe-review.cabr />universe-review.cabr />
universe-review.cali>The third definition of consciousness takes a human-centered view of cognition and has more to do with enlightenment, or illumination, than with mere attention. This is the representational approach, in which consciousness is made dependent upon our human capacity for symbolization. Language is one example of representing something in symbolic form, which expands the power of storing knowledge and information enormously both in space and time (in the forms of books, CD-ROMs, and libraries, ...). This definition relates consciousness exclusively to mental process in the cortex of a human brain.universe-review.cabr />universe-review.cabr />Recent research indicates that consciousness is involved only in activities stemming from the associative regions of the cortex. These regions are found in the neocortex, which consists of four lobes: the occipital, patietal, temporal and frontal. The associative cortex is involved with the conscious perception and identity of one's own body; in the planning of movement, spatial perception, orientation and imagination; and in spatial alertness. The development of consciousness seems to be largely reliant on the numerous nerve cells in the cortex being linked to each others. The cortex's high number of connections vastly exceeds the number of points of entry and exit. This arrangement means that the cortex communicates with itsef more than with the sensory organs and motor apparatus.universe-review.ca/li>
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Most neuroscientists now believe that all aspects of mind, including its most puzzling attribute -- consciousness or awareness -- are likely to be explainable in a more materialistic way as the behavior of large sets of interacting neurons. universe-review.cabr />universe-review.cabr />
universe-review.caul>Modern explanation of consciousness is based on "neural correlate", which assumes:universe-review.cabr />universe-review.cabr />
universe-review.cali>The subjective content associated with a conscious sensation does exist and has its physical basis in the brain.universe-review.ca/li>
universe-review.cali>All the different aspects of consciousness (smelling, pain, visual awareness, self-consciousness, and so on) employ a basic mechanism.universe-review.ca/li>
universe-review.cali>Consciousness is a property of the human brain, a highly evolved system. It therefore must have a useful function to perform, e.g., to produce the best current interpretation of the environment and to make it available to the parts of the brain which contemplate, plan and execute voluntary motor outputs (including language).universe-review.ca/li>
universe-review.cali>At least some animal species posses some aspects of consciousness.universe-review.ca/li>
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It is believed that consciousness is not a thing but a process. The idea of "neural correlates of consciousness" has appeared only in the past few years. It is known that consciousness is always associated with neural activity in a complex brain, and that altering that activity, whether by changes in sensory input, injury, disease, drugs, direct electrical stimulation or neurosurgery, can alter the contents of consciousness. So a reasonable hypothesis is that individual conscious states exist only in association with particular patterns of neural activity. It is these patterns that are referred to as the neural correlates of consciousness (NCC). An example is on the NCC of visual consciousness in monkeys. It has now been determined that neurons in the inferior temporal cortex are responsible for the monkeys to see horizontal or vertical lines.
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universe-review.cah3 align="center">universe-review.caa name="fungi">Fungiuniverse-review.ca/a>universe-review.ca/h3>
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The oldest fossils of fungi date back 460 million years ago. New knowledge on evolutionary lineage shows that they are more closely related to animals than plants. The first vascular plant fossils (dated back to about 400 million years ago) have petried mycorrhizae - indicating that plants and fungi moved onto land together. Mycorrhizae are the roots of fungus, which lives in plant roots where it provides the plant with minerals and the plant gives organic nutrients in return.
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universe-review.catr>universe-review.catd width="25%">universe-review.cah4>Figure 10-29 Bread Mold Life Cycle universe-review.caa href="I10-21-fungi1.jpg">[view large image]universe-review.ca/a>universe-review.ca/h4>universe-review.ca/td>universe-review.catd width="25%">universe-review.cah4>Figure 10-30 Fungi universe-review.caa href="I10-21-fungi2.jpg">[view large image]universe-review.ca/a>universe-review.ca/h4>universe-review.ca/td>universe-review.catd width="50%"> universe-review.ca/td>universe-review.ca/tr>universe-review.ca/table>
universe-review.cap>Fungi lack chloroplasts, as do animals. Thus the process of photosynthesis, which is very common and important in plant life because it serves as their source for food, is absent. Fungi obtain food by heterotrophic process. They secrete enzymes into the nutritive materials. These exoenzymes degrade those substances to which they are adapted, and the resulting compounds must be absorbed through the wall of the cell while leaving the residues (wastes) outside.universe-review.ca/p>
universe-review.cap>The bodies of all fungi, except unicellular yeast, are made up of filaments called hyphae. A hypha is an elongated cylinder containing a mass of cytoplasm and many haploid nuclei, which may or may not be separated by cross wall. A collection of hyphae is called a mycelium.universe-review.ca/p>
universe-review.cap>Fungi reproduce in accordance with the haplontic life cycle as shown in Figure 10-29. This figure shows the life cycle of the black bread mold. Asexually, a mycelium gives rise to spore-producing sporangia. Sexually, the tip ends of hyphae from opposite mating strains can fuse, giving a zygote, the only diploid portion of the cycle. After a period of dormancy, meiosis is followed by germination of the zygospore and production of a sporangium. Windblown spores, an adaptation to land, produce mycelia.universe-review.ca/p>
universe-review.cap>There are many different types of fungi as shown in Figure 10-30. There are sac fungi with saclike cells to store the spores; some have shape like a cup. Yeasts are sac fungi that do not form fruiting bodies; they carry out the fermentation: "glucose => carbon dioxide + alcohol" for either baking or production of wines and beers. The blue-green molds (notably penicillium) are also sac fungi; they are used to provide flavor in cheeses and to produce antibiotic penicillin. Club fungi include the mushroom, which store the spores in the gills under the cap. Some mushrooms are poisonous while other types of fungi cause diseases such as althlete's foot and vaginal infection.universe-review.ca/p>
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universe-review.cah3 align="center">universe-review.caa name="plants">Plantsuniverse-review.ca/a>universe-review.ca/h3>
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universe-review.caa href="I10-22-plants3.jpg">Plantsuniverse-review.ca/a> evolved from green algae in an aquatic evironment about 500 million years ago (see Figure 10-31). There are some 7000 species of green algae living today. They include microscopic, unicellular forms like universe-review.caa href="I10-23-chlorella.gif">chlorellauniverse-review.ca/a> and universe-review.caa href="I10-23-chlamydomonas.jpg">chlamydomonasuniverse-review.ca/a>; colonial forms like the filamentous spirogyra; and multicellular forms like universe-review.caa href="I10-23-ulva.jpg">ulvauniverse-review.ca/a>, the sea lettuce. Although some of the multicellular forms are large, they never develop more than a few differentiated types of cells and their fertilized eggs do not develop into an embryo.
universe-review.ca/td>universe-review.ca/tr>
universe-review.catr>universe-review.catd width="25%">universe-review.cah4>Figure 10-31 Plant Evolution universe-review.caa href="I10-22-plants1.jpg">[view large image]universe-review.ca/a>universe-review.ca/h4>universe-review.ca/td>universe-review.catd width="25%">universe-review.cah4>Figure 10-32 Plant Reproduction universe-review.cabr />universe-review.caa href="I10-22-plants2.jpg">[view large image]universe-review.ca/a>universe-review.ca/h4>universe-review.ca/td>universe-review.catd width="50%"> universe-review.ca/td>universe-review.ca/tr>universe-review.ca/table>
universe-review.cap>About 400 million years ago, plants began to establish themselves on land. The animals soon followed. The following table compares the aquatic and land environments and the kind of adjustments the organisms had to make in order to live on land.universe-review.ca/p>
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universe-review.cath>Wateruniverse-review.ca/th>
universe-review.cath>Landuniverse-review.ca/th>
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universe-review.catd align="center">The surrounding water prevents the organism from drying out; i.e., it prevents desiccation.universe-review.ca/td>
universe-review.catd align="center">To prevent desiccation, the organism obtains water, provides it to all body parts, and possesses a covering that prevents evaporation.universe-review.ca/td>
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universe-review.catd align="center">The surrounding water buoys up the organism and keeps it afloat.universe-review.ca/td>
universe-review.catd align="center">An internal structure helps a large body to oppose the pull of gravity.universe-review.ca/td>
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universe-review.catd align="center">The water prevents desiccation and allows easy transport of reporductive units, such as zoospores and swimming sperm.universe-review.ca/td>
universe-review.catd align="center">In plants, the repoductive units may be adapted to transport by wind currents or by motile animals. Aninals may provide a water environment for swimming sperm.universe-review.ca/td>
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universe-review.catd align="center">The surrounding water prevents the fertilized egg (zygote) from drying out.universe-review.ca/td>
universe-review.catd align="center">The developing zygote is protected from possible desiccation.universe-review.ca/td>
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universe-review.catd align="center">The water maintains a relatively constant environment in regard to temperature, pressure, and moisture.universe-review.ca/td>
universe-review.catd align="center">The organism may be capable of withstanding extreme external fluctuations in temperature, humidity, and wind.universe-review.ca/td>
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universe-review.cah4 align="center">Table 10-04 Water and Land Environments Comparisonuniverse-review.ca/h4>
universe-review.caul>Plants are photosynthetic organisms with the following characteristics:universe-review.cabr />universe-review.cabr />
universe-review.cali>Plants contain chlorophylls; they store reserve food as starch and have cellulose cell walls. Animals store reserve food as glycogen and do not have cellulose cell walls.universe-review.ca/li>
universe-review.cali>Plants lack the power of motion or locomotion by means of contracting fibers.universe-review.ca/li>
universe-review.cali>Plants are multicellular and have cells specialized to from tissues and organs.universe-review.ca/li>
universe-review.cali>Plants have a life cycle that is identified as alternation of generations (see universe-review.caa href="universe-review.ca#lifecycles/default.htm#lifecycles/">Figure 10-06universe-review.ca/a>).universe-review.ca/li>
universe-review.cali>Plants have sex organs with an outer layer of nonreproductive cells that can prevent desiccation of gametes universe-review.cabr />(see Figure 10-32).universe-review.ca/li>
universe-review.cali>Plants protect the developing diploid embryo from drying out by providing it with water and nutrients within the female reproductive structure (see Figure 10-32).universe-review.ca/li>
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universe-review.cap>Land plants first developed as mosses living in moist places. These are fairly simple plants that do produce a number of differentiated cell types and whose fertilized egg grows into a distinct embryo. However, they don't have universe-review.caA NAME="vascular">universe-review.ca/A>universe-review.caa href="I10-24-vascular.jpg">vascular tissueuniverse-review.ca/a>universe-review.casup>universe-review.caa href="universe-review.ca#nine/default.htm#nine/">9universe-review.ca/a>universe-review.ca/sup> (xylem and phloem) to transport water and minerals from their roots up to their leaves. Ferns and horsetails are primitive vascular plants. They still require a wet environment for fertilization to take place. Swamps in the Carboniferous era are believed to have contained universe-review.caa href="I10-31-Carboniferous.jpg">fernlike foliageuniverse-review.ca/a> in great abundance.universe-review.ca/p>
universe-review.cap>As suggested in Table 10-04, land dwelling organisms should be able to support themselves against gravity and to protect their reproductive units from desiccation. These requirements are fulfilled by the vascular tissues and embryo sporophytes in gymnosperms (naked seed) and angiosperms (capsuled seed). Figure 10-32 shows the reproductive cycle of the flowering plants. The first stage of sexual reproduction is pollination. This is the transfer of pollen from the stamen to the stigma. When pollen is carried from the stamen to the stigma of the same plant, the process is called self-pollination. When pollen is carried to the stigma of another plant, it is called cross-collination. Most plants have developed ways of avoiding self-pollination because it reduces genetic variation. When a grain of pollen lands on a stigma, a tube, called a pollen tube, grows from the sigma down into the overy. The male gametes in the pollen pass down this tube and meet the ovule. The fusion results in the formation of a seed which contains a plant embryo. The ovary ripens to form the friut around the seed. In order to prevent overcrowding and competition for space, light, and water, seeds and fruits are carried away from the parent plant by wind, animal or explosion. Further details of plants living through the geological periods from Cambrain to the present are described in an appendix - universe-review.caa href="R10-23-plants.htm">Evolution of Micro-organisms and Plantsuniverse-review.ca/a>.universe-review.ca/p>
universe-review.caa href="default.htm#top/">universe-review.cah4>[Top]universe-review.ca/h4>universe-review.ca/a>
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universe-review.cah3 align="center">universe-review.caa name="animals">Animalsuniverse-review.ca/a>universe-review.ca/h3>
universe-review.catable border="0" width="100%">universe-review.catr>
universe-review.catd width="40%">universe-review.caa href="R10-06-animals.htm">universe-review.caimg src="I10-26-animalsa.jpg" name="Evolution of Animals" alt="Evolution of Animals" align="left" width="350"/>universe-review.ca/a>universe-review.ca/td>
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Animals are believed to have arisen from universe-review.caa href="I10-26-protozoan.jpg">protozoansuniverse-review.ca/a>, which were in existence way back in the Archaean period about 3 billion years ago. These unicellular organisms evolved to multicelluar organisms called metazoa over 600 million years ago. Primitive metazoa can be grouped in three basic categories: sponge-like animals, cnidarians, and worms. The sponges, and cnidarians, are the most primitive with about 11 specialized cell types. Worms and higher metazoa have approximately 55 specialized cells.universe-review.cabr />
universe-review.caa href="I10-26-sponge.jpg">Spongesuniverse-review.ca/a> are the simplest grade of multi-celled animals. In general, sponges have open-topped, sack-like bodies which are fixed to the sea floor. Water is pulled through pores in the body, and food is filtered out; rest of the water exits from the opening.universe-review.cabr />
The universe-review.caa href="I10-35-cnidaria.jpg">cnidariansuniverse-review.ca/a> include universe-review.caa href="I10-26-coral.jpg">coralsuniverse-review.ca/a>, universe-review.caa href="I10-26-hydra.jpg">hydrasuniverse-review.ca/a>, universe-review.caa href="I10-26-seaanemone.jpg">sea anemonesuniverse-review.ca/a>, and universe-review.caa href="I10-26-jellyfish.jpg">jellyfishuniverse-review.ca/a>. Their basic body plan is also a sack-like form, but at one end there is a mouth/anus, which can be opened and closed, and tentacles which direct food to the mouth.
universe-review.ca/td>universe-review.ca/tr>
universe-review.catr>universe-review.catd width="40%">universe-review.cah4>Figure 10-33 Animal Evolution universe-review.caa href="R10-06-animals.htm">[view large image]universe-review.ca/a>universe-review.ca/h4>universe-review.ca/td>universe-review.ca/tr>universe-review.ca/table>
Worms are the most advanced grade of simple metazoan, and it is this body plan from which all higher animals evolved. Worms have a fluid-filled cavity called a coelom inside the body and variations of this cavity can be seen in all higher animals. In many animals, it has become the sack, which holds the internal organs.
universe-review.cap>Figure 10-33 shows animal diversification over the age. Further details of animals evolving through the geological periods from Cambrain to the present are described in an appendix - universe-review.caa href="R10-19-animals.htm">Age of Animalsuniverse-review.ca/a>. The living animals are described in the universe-review.caa href="R10-33-anatomy.htm">Anatomy of Animalsuniverse-review.ca/a>.universe-review.ca/p>
universe-review.caa href="default.htm#top/">universe-review.cah4>[Top]universe-review.ca/h4>universe-review.ca/a>
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universe-review.cah3 align="center">universe-review.caa name="humans">What Makes Us Humansuniverse-review.ca/a>universe-review.ca/h3>
The question of "What makes us humans" has been pondered by philosophers and others since time immemorial. The answer is usually implied in the definition of humans. We can draw up a list of differences: bodily differences such as the plantigrade (flat to the floor) foot, opposable thumbs, bipedal gait and big brains; mental differences in intelligence, speech, imagination,
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tool manufacture and use, fire and cooking; and social differences in culture, religion, music, art, reason, use of medicine, social learning and the formation of social groups. Such list would separate us more or less from the other animals. Genetically, recent study in 2004 by comparing the sequence of chimpanzee (Figure 10-34a) chromosome 22 with the equivalent human chromosome 21 reveals that 1.5% of the former consists of single-base substitutions, in addition to nearly 68000 insertions or deletions. That's sufficient to generate changes in most proteins.
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universe-review.catr>universe-review.catd width="10%">universe-review.cah4>Figure 10-34a Chimpanzee universe-review.ca/h4>universe-review.ca/td>
universe-review.catd width="20%">universe-review.cah4>Figure 10-34b Tool-maker universe-review.caa href="I10-74-human.jpg">[view large image]universe-review.ca/a>universe-review.ca/h4>universe-review.ca/td>universe-review.ca/tr>universe-review.ca/table>
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universe-review.catd width="20%">universe-review.caa href="I10-80-adolescence.jpg">universe-review.caimg src="I10-80-adolescence.jpg" name="Adolescence Brain" alt="Adolescence Brain" align="left" width="200"/>universe-review.ca/a>universe-review.ca/td>
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A new study has found the strongest evidence yet in the brain's right prefrontal cortex (Figure 10-35) that sets humans apart from other primates. This is the site where we understand the mental processes of others - the basis of our socialization and what makes us humans. It gives rise to our capacity to feel empathy, sympathy, understand humor and when others are being ironic, sarcastic or even deceptive. It is the cumulative result of 300,000 years of tool-making evolution (Figure 10-34b), which requires the ordering of sequences and the hierarchical assembly of the same components into different configurations (to make tools of different functions). As makers of single-component tools, we progressed at a remarkably slow pace starting about 2.5 million years ago. But with the appearance of composite tools, near-modern brain size anatomy and perhaps of
universe-review.ca/td>universe-review.ca/tr>
universe-review.catr>universe-review.catd width="20%">universe-review.cah4>Figure 10-35 Adolescence Brain universe-review.caa href="I10-80-adolescence.jpg">[view large image]universe-review.ca/a>universe-review.ca/h4>universe-review.ca/td>
universe-review.catd width="80%">grammatical language 300,000 years ago, the pace quickened exponentially. We became long-range planners and grammatical speakers. Eventually, we possess all the prefrontal capacities - working memory, our sense of self, and theorizing about other people's minds. universe-review.ca/td>universe-review.ca/tr>universe-review.ca/table>
The so-called intentionality now constitutes the essential ingredient for the new definition of humans. However, it is still not completely distinctive. Human children cannot distinguish between their own intentions and those of others until the age of four. Such ability develops gradually over the years, continuing well into adolescence. It is known that some parts of the brain are still developing in that age. They are responsible for many problems associated with teenagers' unique behavioural traits (see Figure 15-35). It is also doubtful that other animals can survive without the ability to read the intention of others and to evaluate the potential for reward and danger. universe-review.cabr />universe-review.cabr />
universe-review.caa href="default.htm#top/">universe-review.cah4>[Top]universe-review.ca/h4>universe-review.ca/a>
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universe-review.cah3 align="center">universe-review.caa name="model">Future of the Human Raceuniverse-review.ca/a>universe-review.ca/h3>
universe-review.catable border="0" width="100%">universe-review.catr>
universe-review.catd width="20%">universe-review.caa href="I10-79-worldmodel1.jpg">universe-review.caimg src="I10-79-worldmodel1.jpg" name="World Model 1" alt="World Model 1" align="left" width="196"/>universe-review.ca/a>universe-review.ca/td>
universe-review.catd width="20%">universe-review.caa href="I10-79-worldmodel2.jpg">universe-review.caimg src="I10-79-worldmodel2.jpg" name="World Model 2" alt="World Model 2" align="left" width="200"/>universe-review.ca/a>universe-review.ca/td>
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Figures 10-36 and 10-37 show two world models among many others, which were built specifically to investigate five major trends of global concern - accelerating industrialization, rapid population growth, widespread malnutrition, depletion of nonrenewable resources, and a deteriorating environment. Like every other model, they are imperfect, oversimplified, and unfinished. The model uses feedback loop similar to the universe-review.caa href="R01-09-chaos.htm#logistic">logistic equationuniverse-review.ca/a> to trace the development of the eight variables as labeled without scales in the diagrams. The
universe-review.ca/td>universe-review.ca/tr>
universe-review.catr>universe-review.catd width="20%">universe-review.cah4>Figure 10-36 World Model, Standard universe-review.caa href="I10-79-worldmodel1.jpg">[view large image]universe-review.ca/a>universe-review.ca/h4>universe-review.ca/td>
universe-review.catd width="20%">universe-review.cah4>Figure 10-37 World Model, Controlled universe-review.caa href="I10-79-worldmodel2.jpg">[view large image]universe-review.ca/a>universe-review.ca/h4>universe-review.ca/td>universe-review.catd width="60%">horizontal time scale is also vague because the model just indicates the general behavior, the numerical values are not as significant as some critic would like to ascribe. universe-review.ca/td>universe-review.ca/tr>universe-review.ca/table>
The original idea of world model came from J. Forrester of MIT at a "Club of Rome" (billed as a global think tank and centre of innovation and initiative) meeting in 1970. The study was conducted by an international team with financial support from the Volkswagen Foundation. The research has been completed by 1972 with the publication of "universe-review.cai>The Limits to Growthuniverse-review.ca/i>". While critic in the 21st century points out that the dire prediction in the models has not been materialized in the 1990's, the proponents maintain that the warning from the "Club of Rome" remains valid. There are already situations where the trends have been realized. It seems that both sides of the debate have over-estimated the power of a model. Any computer model is, by definition, a simplified version of the real world, its predictions vulnerable to some neglected factor or changing circumstance. universe-review.cai>The Limits to Growthuniverse-review.ca/i> just revealed some important aspects of the challenges faced by society today. universe-review.cabr />universe-review.cabr />
Figure 10-36 is the "standard" world model, which assumes no major change in the physical, economic, or social relationships that have historically governed the development of the world system. All variables plotted follow the historical values from 1900 to 1970. Food, industrial output, and population grow exponentially until the rapidly diminishing resource base forces a slowdown in industrial growth. Because of natural delays in the system, both population and pollution continue to increase for some time after the peak of industrialization. Population growth is finally halted by a rise in the death rate due to decreased food and medical services. universe-review.cabr />universe-review.cabr />
universe-review.caul>Different models can be constructed easily by changing the value of parameters in the computer programs. The followings summarizes the essential features in these models:universe-review.cabr />universe-review.cabr />
universe-review.cali>Doubling the resource reserves in 1900 or assuming "unlimited" nuclear power do not change the outcome as the growth in other variables are stopped by rising pollution.universe-review.ca/li>
universe-review.cali>World model with "unlimited" resources and pollution controls allow population and industry to grow until the limit of arable land is reached. Food per capita declines, and industrial growth is also slowed as capital is diverted to food production. Population decline is delayed for about 30 years.universe-review.ca/li>
universe-review.cali>The combination of "unlimited" resources, pollution controls, and increased agricultural productivity removes so many constraints to growth that population and industry reach very high levels. Although each unit of industrial production generates much less pollution, total production rises enough to create a pollution crisis that brings an end to growth.universe-review.ca/li>
universe-review.cali>Instead of an increase in food production, an increase in birth control effectiveness is tested as a policy to avert the food problem. It shows that population continues to grow, but more slowly. Nevertheless, the food crisis is postponed for only a decade or two.universe-review.ca/li>
universe-review.cali>Figure 10-37 is a world model with "unlimited" resources, pollution controls, increased agricultural productivity, and "perfect" birth control. The result is a temporary achievement of a constant population with a world average income per capita that reaches nearly the present US level. Finally, though, industrial growth is halted, and the death rate rises as resources are depleted, pollution accumulates, and food production declines. Population decline is delayed for about 50 years.universe-review.ca/li> universe-review.ca/ul>
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universe-review.catd width="20%">universe-review.caa href="I10-79-worldmodel3.jpg">universe-review.caimg src="I10-79-worldmodel3.jpg" name="World Model 1" alt="World Model 1" align="left" width="190"/>universe-review.ca/a>universe-review.ca/td>
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It has been shown that positive feedback loops operating without any constraints generate exponential growth. In the world system two positive feedback loops are dominant now, producing exponential growth of population and of industrial capital. In any stabilized system there must be constraints acting as feedback loops to stop exponential growth. The growth stopping pressures from negative feedback loops are already being felt in many parts of human society. Another response to the problems created by growth would be to weaken the positive feedback loops that are generating the growth. Such solution involves growth-regulating policies, which generates a "better" behavior mode. Figure 10-38 shows a world model with regulating policies to produce an equilibrium state sustainable far into the future.
universe-review.ca/td>universe-review.ca/tr>
universe-review.catr>universe-review.catd width="20%">universe-review.cah4>Figure 10-38 World Model, Stabilized universe-review.caa href="I10-79-worldmodel3.jpg">[view large image]universe-review.ca/a>universe-review.ca/h4>universe-review.ca/td>universe-review.catd width="80%"> universe-review.ca/td>universe-review.ca/tr>universe-review.ca/table>
universe-review.caol>The policies that produced the stabilized world model are:universe-review.cabr />universe-review.cabr />
universe-review.cali>Population is stabilized by setting the birth rate equal to the death rate in 1975. Industrial capital is allowed to increase naturally until 1990, after which it, too, is stabilized, by setting the investment rate equal to the depreciation rate.universe-review.ca/li>
universe-review.cali>To avoid a nonrenewable resource shortage, resource consumption per unit of industrial output is reduced to 1/4 of its 1970 value.universe-review.ca/li>
universe-review.cali>To further reduce resource depletion and pollution, the economic preferences of society are shifted more toward services such as education and health facilities and less toward factory-produced material goods.universe-review.ca/li>
universe-review.cali>Pollution generation per unit of industrial and agricultural output is reduced to 1/4 of its 1970 value.universe-review.ca/li>
universe-review.cali>To avoid food shortage, capital is diverted to food production even if such an investment would be considered "uneconomic".universe-review.ca/li>
universe-review.cali>This policy alters the use of agricultural capital to make soil enrichment and preservation. It implies, for example, use of capital to compost urban organic wastes and return them to the land.universe-review.ca/li>
universe-review.cali>To counteract the drains on industrial capital resulting from the above-mentioned policies, the average lifetime of industrial capital in increased, implying better design for durability and repair and less discarding because of obsolescence. This policy also tends to reduce resource depletion and pollution.
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Implementation of this set of policies required government intervention and control of industrial and agricultural activities as well as family planning and also implies interference of people's daily life. Certainly, it would generate a lot of resistance, and there would be many non-believers. New approach have been developed by focusing on flexibility to strike a balance between the economy and the environment (e.g., we can set a goal for cutting pollution but relax the deadline if the cost runs too high). universe-review.cabr />universe-review.cabr />
universe-review.caol>The conclusions of universe-review.cai>The Limit of Growthuniverse-review.ca/i>:universe-review.cabr />universe-review.cabr />
universe-review.cali>If the present growth trends in world population, industrialization, pollution, food production, and resource depletion continue unchanged, the limits to growth on this planet will be reached sometime within the next 100 years. The most probable result will be a rather sudden and uncontrollable decline in both population and industrial capacity.universe-review.ca/li>
universe-review.cali>It is possible to alter these growth trends and to establish a condition of ecological and economic stability that is sustainable far into the future.universe-review.ca/li>
universe-review.cali>If the world's people decide to strive for this second outcome rather the first, the sooner they begin working to attain it, the greater will be their chances of success. That is, the sooner the better.universe-review.ca/li>universe-review.ca/ol>
There are plenty of examples for civilization in ruins. The Maya, the Anasazi, the Easter Island, ...are known cases of failed societies. The universe-review.caa href="I10-81-Maya.jpg">Mayauniverse-review.ca/a> had the technological knowledge to build architecturally wonderful cities (Figure 10-39). What they did not have were large domestic animals, or the foresight to replant after they clear-cut forests, or the political sense to refrain from inter-city warfare. They began to go into decline about A.D. 1000 and were finished off by the Spaniards about 1675. The universe-review.caa href="I10-81-Anasazi.jpg">Anasaziuniverse-review.ca/a>, settled in the New Mexico area about A.D. 600. There they built spectacular cliff housing, worked their marginal agricultural land, and chopped down all the trees without any plans for reforestation. Starving to the point of cannibalism, wracked by internecine warfare, they met their end some 600 years later. Other fallen Island societies, such as the one on universe-review.caa href="I10-81-EasterIsland.jpg">Eastern Islanduniverse-review.ca/a>, all collapsed after the settlers had exhausted the fragile food and timber resources. Deforestation (Figure
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10-40) was particularly critical; after the larger trees were harvested, nothing was left to make the seagoing canoes needed for voyaging to other sources of food and material. A common thread in the catastrophic collapse of past civilizations is a tendency to impose self-inflicted environmental degration, and unwise responses to societal problems such as using war as an instrument to resolve
universe-review.ca/td>universe-review.ca/tr>
universe-review.catr>universe-review.catd width="15%">universe-review.cah4>Figure 10-39 Mayan Civili-universe-review.cabr />zation universe-review.caa href="I10-81-Maya2.jpg">[view large image]universe-review.ca/a>universe-review.ca/h4>universe-review.ca/td>
universe-review.catd width="25%">universe-review.cah4>Figure 10-40 Deforestation universe-review.cabr />universe-review.caa href="I10-81-deforestation.jpg">[view large image]universe-review.ca/a>universe-review.ca/h4>universe-review.ca/td>
universe-review.catd width="60%">disputes, which mostly involve the sharing of resources - it is mostly about oil in this epoch of civilization.universe-review.cabr />universe-review.cabr />universe-review.ca/td>
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universe-review.caa href="default.htm#top/">universe-review.cah4>[Top]universe-review.ca/h4>universe-review.ca/a>
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universe-review.cah3 align="center">universe-review.caa name="footnotes">Footnotesuniverse-review.ca/a>universe-review.ca/h3>
universe-review.cap>universe-review.caA NAME="one">universe-review.ca/A>universe-review.casup>1universe-review.ca/sup>Since the volume increases faster than the surface area, a single cell cannot enlarge its size indefinitely. It has a limit beyond which the surface area is not capable of absorbing enough nutrition (including oxygen) and draining off excessive waste.universe-review.ca/p>
universe-review.cap>universe-review.caA NAME="two">universe-review.ca/A>universe-review.casup>2universe-review.ca/sup>Sexual reproducation endows genetic variations and replaces damaged genes. Cloning negates these evolutionary advantages by skipping the haploid phase of the life cycle (see Figure 10-05). universe-review.caa href="I10-16-Dolly.jpg">Dollyuniverse-review.ca/a>, the world's first cloned sheep has died on February, 2003 at the age of 6 after a veterinary examination confirmed the lung disease. Sheep can live to 11 or 12 years of age and lung infections are common in older sheep, particularly those housed inside. She has developed other old age symptoms such as arthritis, a condition usually expected in older animals. Research in 1999 suggested that Dolly might be susceptible to premature ageing -- a possibility raised after a study of her genetics. universe-review.ca/p>
universe-review.cap>universe-review.caA NAME="three">universe-review.ca/A>universe-review.casup>3universe-review.ca/sup>A gene is defined to be a section of DNA that transcribes a protein. The gene expression (transcription) is initiateed by binding the transcription factor (such as the homeodomain) to the beginning section of the gene called the promoter.universe-review.ca/p>
universe-review.cap>universe-review.caA NAME="four">universe-review.ca/A>universe-review.casup>4universe-review.ca/sup>Protein is produced from universe-review.caa href="I01-06-DNA.jpg">DNAuniverse-review.ca/a> via the universe-review.caa href="I10-11-DNAprotein.jpg">transcription/translation processuniverse-review.ca/a>. The base (nucleotide) Thymine (T) becomes Uracil (U) in the transcription from DNA to RNA. Three bases translate into one amino acid according to the universe-review.caa href="I10-11-geneticode.jpg">genetic codeuniverse-review.ca/a>. The amino acids link together to form a protein.universe-review.ca/p>
universe-review.cap>universe-review.caA NAME="five">universe-review.ca/A>universe-review.casup>5universe-review.ca/sup>Male germ cells (sperms) are produced continuously in the testes throughout life. About 50,000 female germ cells (eggs) are prepared in the ovaries of the female embryo 12 days after fertilization. It is reported in 2004 that stem cells for oocytes (immature female reproductive cells) are found within the ovaries of mice in contrary to traditional believe.universe-review.ca/p>
universe-review.cap>universe-review.caa name="six">universe-review.ca/a>universe-review.casup>6universe-review.ca/sup>Even though if cellular damage by external causes can be avoided, an inherent problem is bound to arise by internal metabolism. The metabolic pathway in mitochondria relies on the transportaton of free electrons, which eventually attach to oxygen and are normally neutralized by hydrogen ion to form water. This is usually referred to as universe-review.caa href="F11-monocell.htm#respiration">respirationuniverse-review.ca/a>. Sometimes the process breaks down, the electrons do not attach to the oxygen and instead, attach to other oxygen species. Specific molecules, each carrying a wayward electron, were created. They are call free radicals (such as hydroxyl, superoxide and peroxide - collectively called reactive oxygen species or universe-review.caa href="R10-21-ROS.htm">ROSuniverse-review.ca/a>). These free radicals are highly reactive and can do tremendous damage to the cell. The ROS can indiscriminately damage anything that gets in their way - proteins, fats, RNA, and DNA. The effect is cumulative and a serious problem will occur if ROS numbers get too high. Not surprisingly, the cell has responded to this threat by creating various enzymes that bind to free-radicals and inactivate them. Collectively, molecules that destroy free radicals are called anti-oxidants. Aging is probably the result of the breakdown in the cellular safety nets - not enough anti-oxidants are produced naturally. In addition, modern life has enormously increased the number of toxic free-radicals introduced into our bodies every day from the surrounding environment. The most significant sources of excess free-radicals are dietary or environmental. Dietary sources are usually fats, either rancid or hydrogenated fats, and fats that have been heated to high temperatures during cooking. Environmental pollutants include automobile exhaust, cigarette smoke and numerous other chemicals, physical exercise, stress, and radiation. To increase the defence against these ROS, it is suggested that consumption of special kinds of foods, herbs, and dietary supplements (including vitamins C and E, beta carotene and selenium) will scavenge excess free-radicals and provide raw materials necessary for the body to produce antioxidant enzymes. Recently, it is observed that the most efficient way to delay aging is through caloric restriction. It is found that by reducing 30 - 40 percent the calories in an animal's diet, results in healthy and long-lived mice and rats. It seems that the animals have switched their metabolism from a pro-growth mode to a pro-repair mode. The latest research tries to manuplate the level of the IGF-1 (insulin-like growth factor-1) protein so that people can maintain the pro-repair mode without diet restriction.universe-review.ca/p>
universe-review.cap>universe-review.caA NAME="seven">universe-review.ca/A>universe-review.casup>7universe-review.ca/sup>The biofeedback technique uses electronics to detect and amplify internal body activities too subtle for normal awareness. One of such methods is the galvanic skin resistance (GSR). It utilizes the fact that skin resistance increases in a calm and relaxed state; it goes the other way at tensing up even slightly. The difference is a reflection of variations in the sweat gland activity and pore size, both of which are controlled by the universe-review.caa href="R10-16-ANS.htm">autonomic nervous systemuniverse-review.ca/a>. When the fingers are placed on the sensing plates of the GSR device, the tone lowers with progressive relaxation. The objective is to relax by learning how to diminish the tone of the GSR device to the lowest point possible.universe-review.ca/p>
universe-review.cap>universe-review.caA NAME="eight">universe-review.ca/A>universe-review.casup>8universe-review.ca/sup>Mind is defined as the mental activity, which includes both conscious and unconscious processes, thus mind has a broader meaning than consciousness.universe-review.ca/p>
universe-review.cap>universe-review.caA NAME="nine">universe-review.ca/A>universe-review.casup>9universe-review.ca/sup>Vascular tissue is made up of two parts: xylem and phloem. Xylem carries water and minerals up the plant. Phloem carries dissolved foods such as glucose around the plant. Transpiration is the evaporation of water out of the plant, through pores in the leaves called stomato. As transpiration takes place, water is forced up the stem xylem and into the leaves, to replace the water that is lost.universe-review.ca/p>
universe-review.caa href="default.htm#top/">universe-review.cah4>[Top]universe-review.ca/h4>universe-review.ca/a>
universe-review.cahr align="center" width="15%" />
universe-review.caul>universe-review.cah3>universe-review.caa name="references">References:universe-review.ca/a>universe-review.ca/h3>
universe-review.cali>Five Kingdoms, Details -- universe-review.caa href="http://waynesword.palomar.edu/trfeb98.htm">http://waynesword.palomar.edu/trfeb98.htm universe-review.ca/a>universe-review.ca/li>
universe-review.cali>Five Kingdoms, Short Table -- universe-review.caa href="http://curie.uncg.edu/~esmith/kingdom.html">http://curie.uncg.edu/~esmith/kingdom.htmluniverse-review.ca/a>universe-review.ca/li>
universe-review.cali>Evolutionary Tree -- universe-review.caa href="http://www.phy.auckland.ac.nz/old/354sc/html/p6_p8.html">http://www.phy.auckland.ac.nz/old/354sc/html/p6_p8.htmluniverse-review.ca/a>
universe-review.ca/li>
universe-review.cali>Multicellular Organisms, Origin -- universe-review.caa href="http://www.devbio.com/chap22/link2203.shtml">http://www.devbio.com/chap22/link2203.shtmluniverse-review.ca/a>universe-review.ca/li>
universe-review.cali>Sexual Life Cycle -- universe-review.caa href="http://bama.ua.edu/~ksuberkp/bsc114/Lectures/B14meios.htm">http://bama.ua.edu/~ksuberkp/bsc114/Lectures/B14meios.htmuniverse-review.ca/a>universe-review.ca/li>
universe-review.cali>Sexual Life Cycle, Plants -- universe-review.caa href="http://www-plb.ucdavis.edu/courses/f98/bis1a/LifeCycl.htm">http://www-plb.ucdavis.edu/courses/f98/bis1a/LifeCycl.htmuniverse-review.ca/a>universe-review.ca/li>
universe-review.cali>Slime Moulds -- universe-review.caa href="http://www.this-magic-sea.com/COMCELL.HTM">http://www.this-magic-sea.com/COMCELL.HTMuniverse-review.ca/a> universe-review.ca/li>
universe-review.cali>Homeobox Genes -- universe-review.caa href="http://homeobox.biosci.ki.se/">http://homeobox.biosci.ki.se/universe-review.ca/a>universe-review.ca/li>
universe-review.cali>Body Plans, Animals -- universe-review.caa href="http://www.bio.indiana.edu/courses/L111-Bever/class%20notes/OCT22-24Protists_to_Animals.htm">http://www.bio.indiana.edu/courses/L111-Bever/class%20notes/OCT22-24Protists_to_Animals.htmuniverse-review.ca/a>universe-review.ca/li>
universe-review.cali>Stem Cells -- universe-review.caa href="http://www.nih.gov/news/stemcell/primer.htm">http://www.nih.gov/news/stemcell/primer.htmuniverse-review.ca/a>universe-review.ca/li>
universe-review.cali>universe-review.caa name="ref1">universe-review.ca/a>Embryonic Stem Cell Policy (US) -- universe-review.caa href="http://www.bioethics.gov/background/es_moralfoundations.html">http://www.bioethics.gov/background/es_moralfoundations.htmluniverse-review.ca/a>universe-review.ca/li>
universe-review.cali>Sex and Death -- universe-review.caa href="http://www.dhushara.com/book/sci/sexdeth.htm">http://www.dhushara.com/book/sci/sexdeth.htmuniverse-review.ca/a>universe-review.ca/li>
universe-review.cali>Biological Clock -- universe-review.caa href="http://cal.man.ac.uk/student_projects/1999/sanders/home1.htm">http://cal.man.ac.uk/student_projects/1999/sanders/home1.htmuniverse-review.ca/a>universe-review.ca/li>
universe-review.cali>Clock of Ages -- New Scientist, vol. 178, issue 2391 - 19 April 2003, page 26. (universe-review.caa href="R10-05-ageing.doc">Reprintuniverse-review.ca/a>)universe-review.ca/li>
universe-review.cali>Cloning, Facts about -- universe-review.caa href="http://www.ornl.gov/TechResources/Human_Genome/elsi/cloning.html#intro">http://www.ornl.gov/TechResources/Human_Genome/elsi/cloning.html#introuniverse-review.ca/a>universe-review.ca/li>
universe-review.cali>History of the Earth -- universe-review.caa href="http://www.bio.miami.edu/tom/bil160/bil160goods/09_platetec.html">http://www.bio.miami.edu/tom/bil160/bil160goods/09_platetec.htmluniverse-review.ca/a>universe-review.ca/li>
universe-review.cali>Paleontology -- universe-review.caa href="http://www.awesomelibrary.org/Classroom/Science/Paleontology/Paleontology.html">http://www.awesomelibrary.org/Classroom/Science/Paleontology/Paleontology.htmluniverse-review.ca/a>universe-review.ca/li>
universe-review.cali>Life on Earth -- universe-review.caa href="http://www.palaeos.com/Default.htm">http://www.palaeos.com/Default.htmuniverse-review.ca/a>universe-review.ca/li>
universe-review.cali>Cambrian Explosion -- universe-review.caa href="http://biocrs.biomed.brown.edu/Books/Chapters/Ch%2019/Fossil-Embryos/Time-Cambrian.html">http://biocrs.biomed.brown.edu/Books/Chapters/Ch%2019/Fossil-Embryos/Time-Cambrian.htmluniverse-review.ca/a>universe-review.ca/li>
universe-review.cali>Animal Kingdom -- universe-review.caa href="http://www.swishweb.com/Animal_Kingdom/">http://www.swishweb.com/Animal_Kingdom/universe-review.ca/a>universe-review.ca/li>
universe-review.cali>Animal Evolution, Slide Show -- universe-review.caa href="http://www.uwinnipeg.ca/~simmons/Chap3298/sld001.htm">http://www.uwinnipeg.ca/~simmons/Chap3298/sld001.htmuniverse-review.ca/a>universe-review.ca/li>
universe-review.cali>Animal Phyla, Present Day -- universe-review.caa href="http://www.sidwell.edu/us/science/vlb5/Labs/Classification_Lab/Eukarya/Animalia/">http://www.sidwell.edu/us/science/vlb5/Labs/Classification_Lab/Eukarya/Animalia/universe-review.ca/a>universe-review.ca/li>
universe-review.cali>Becoming Human, Interactive Documentary -- universe-review.caa href="http://www.becominghuman.org/">http://www.becominghuman.org/universe-review.ca/a>universe-review.ca/li>
universe-review.cali>Human Origins and Evolution in Africa -- universe-review.caa href="http://www.indiana.edu/~origins/">http://www.indiana.edu/~origins/universe-review.ca/a>universe-review.ca/li>
universe-review.cali>New Look at Human Evolution -- Scientific American, Special Edition, 2003universe-review.ca/li>
universe-review.cali>Evolution of the Brain -- universe-review.caa href="http://primatesociety.com/Into/survival/timeline/timeline.html">http://primatesociety.com/Into/survival/timeline/timeline.htmluniverse-review.ca/a>universe-review.ca/li>
universe-review.cali>Anatomy of the Human Brain -- universe-review.caa href="http://sprojects.mmi.mcgill.ca/brain/contents.htm">http://sprojects.mmi.mcgill.ca/brain/contents.htmuniverse-review.ca/a>universe-review.ca/li>
universe-review.cali>Overview of the Brain -- universe-review.caa href="http://brain.web-us.com/brain/aboutthebrain.htm">http://brain.web-us.com/brain/aboutthebrain.htmuniverse-review.ca/a>universe-review.ca/li>
universe-review.cali>Biology of Consciousness -- universe-review.caa href="http://www.colorado.edu/Honors/honr4000-882dubin/projects/sujatha/index.html">http://www.colorado.edu/Honors/honr4000-882dubin/projects/sujatha/index.htmluniverse-review.ca/a>universe-review.ca/li>
universe-review.cali>Neural Correlates of Consciousness -- universe-review.caa href="http://www.u.arizona.edu/~chalmers/papers/ncc2.html">http://www.u.arizona.edu/~chalmers/papers/ncc2.htmluniverse-review.ca/a>universe-review.ca/li>
universe-review.cali>Sleep and Dream -- universe-review.caa href="http://faculty.washington.edu/chudler/sleep.html">http://faculty.washington.edu/chudler/sleep.htmluniverse-review.ca/a> universe-review.ca/li>
universe-review.cali>Sleep and Dream -- universe-review.caa href="http://hcs.harvard.edu/~husn/BRAIN/vol1/sleep.html">http://hcs.harvard.edu/~husn/BRAIN/vol1/sleep.html>universe-review.ca/a>universe-review.ca/li>
universe-review.ca/ul>
universe-review.caa href="default.htm#top/">universe-review.cah4>[Top]universe-review.ca/h4>universe-review.ca/a>
universe-review.cahr align="center" width="15%" />
universe-review.cah3>universe-review.caa name="Index">Indexuniverse-review.ca/a>universe-review.ca/h3>
universe-review.catable border="0" width="100%">universe-review.catr>
universe-review.catd width="49%">
universe-review.caa href="R10-27-ageing.htm">Ageinguniverse-review.ca/a>universe-review.cabr />
universe-review.caa href="universe-review.ca#allelic/default.htm#allelic/">Allelic pairsuniverse-review.ca/a>universe-review.cabr />
universe-review.caa href="universe-review.ca#animals/default.htm#animals/">Aminalsuniverse-review.ca/a>universe-review.cabr />
universe-review.caa href="universe-review.ca#six/default.htm#six/">Antioxidantuniverse-review.ca/a>universe-review.cabr />
universe-review.caa href="universe-review.ca#archaea/default.htm#archaea/">Archaeauniverse-review.ca/a>universe-review.cabr />
universe-review.caa href="R10-19-animals.htm#archaeopteryx">Archaeopteryxuniverse-review.ca/a>universe-review.cabr />
universe-review.caa href="universe-review.ca#axon/default.htm#axon/">Axonuniverse-review.ca/a>universe-review.cabr />
universe-review.caa href="universe-review.ca#bacteria/default.htm#bacteria/">Bacteriauniverse-review.ca/a>universe-review.cabr />
universe-review.caa href="universe-review.ca#basal/default.htm#basal/">Basal layeruniverse-review.ca/a>universe-review.cabr />
universe-review.caa href="universe-review.ca#ten/default.htm#ten/">Biofeedbackuniverse-review.ca/a>universe-review.cabr />
universe-review.caa href="universe-review.ca#clock/default.htm#clock/">Biological clockuniverse-review.ca/a>universe-review.cabr />
universe-review.caa href="universe-review.ca#classifications/default.htm#classifications/">Biological classificationsuniverse-review.ca/a>universe-review.cabr />
universe-review.caa href="universe-review.ca#cavity/default.htm#cavity/">Body Cavity (Coelom)universe-review.ca/a>universe-review.cabr />
universe-review.caa href="universe-review.ca#bone/default.htm#bone/">Bone marrowuniverse-review.ca/a>universe-review.cabr />
universe-review.caa href="R10-19-animals.htm#bony">Bony Fishuniverse-review.ca/a>universe-review.cabr />
universe-review.caa href="universe-review.ca#brain/default.htm#brain/">Brainuniverse-review.ca/a>universe-review.cabr />
universe-review.caa href="universe-review.ca#waves/default.htm#waves/">Brain wavesuniverse-review.ca/a>universe-review.cabr />
universe-review.caa href="R10-19-animals.htm#Burgess">Burgess Shaleuniverse-review.ca/a>universe-review.cabr />
universe-review.caa href="R10-19-animals.htm#Cambrian">Cambrian Perioduniverse-review.ca/a>universe-review.cabr />
universe-review.caa href="universe-review.ca#cAMP/default.htm#cAMP/">cAMPuniverse-review.ca/a>universe-review.cabr />
universe-review.caa href="R10-19-animals.htm#Carboniferous">Carboniferous Perioduniverse-review.ca/a>universe-review.cabr />
universe-review.caa href="universe-review.ca#cloning/default.htm#cloning/">Cloninguniverse-review.ca/a>universe-review.cabr />
universe-review.caa href="universe-review.ca#conjugation/default.htm#conjugation/">Conjugationuniverse-review.ca/a>universe-review.cabr />
universe-review.caa href="universe-review.ca#consciousness/default.htm#consciousness/">Consciousnessuniverse-review.ca/a>universe-review.cabr />
universe-review.caa href="R10-19-animals.htm#Cretaceous">Cretaceous Perioduniverse-review.ca/a>universe-review.cabr />
universe-review.caa href="universe-review.ca#dendrites/default.htm#dendrites/">Dendritesuniverse-review.ca/a>universe-review.cabr />
universe-review.caa href="R10-19-animals.htm#Devonian">Devonian Perioduniverse-review.ca/a>universe-review.cabr />
universe-review.caa href="R10-19-animals.htm#dinosaurs">Dinosaursuniverse-review.ca/a>universe-review.cabr />
universe-review.caa href="universe-review.ca#diploid/default.htm#diploid/">Diploiduniverse-review.ca/a>universe-review.cabr />
universe-review.caa href="universe-review.ca#dream/default.htm#dream/">Dreamuniverse-review.ca/a>universe-review.cabr />
universe-review.caa href="universe-review.ca#germlayers/default.htm#germlayers/">Ectodermuniverse-review.ca/a>universe-review.cabr />
universe-review.caa href="universe-review.ca#embryo/default.htm#embryo/">Embryouniverse-review.ca/a>universe-review.cabr />
universe-review.caa href="universe-review.ca#embryonic/default.htm#embryonic/">Embryonic developmentuniverse-review.ca/a>universe-review.cabr />
universe-review.caa href="universe-review.ca#germlayers/default.htm#germlayers/">Endodermuniverse-review.ca/a>universe-review.cabr />
universe-review.caa href="universe-review.ca#eukaryotes/default.htm#eukaryotes/">Eukaryotesuniverse-review.ca/a>universe-review.cabr />
universe-review.caa href="universe-review.ca#evolution/default.htm#evolution/">Evolution of multicellular organismsuniverse-review.ca/a>universe-review.cabr />
universe-review.caa href="universe-review.ca#etree/default.htm#etree/">Evolutionary Treeuniverse-review.ca/a>universe-review.cabr />
universe-review.caa href="universe-review.ca#kingdoms/default.htm#kingdoms/">Five Kingdomsuniverse-review.ca/a>universe-review.cabr />
universe-review.caa href="universe-review.ca#six/default.htm#six/">Free radicaluniverse-review.ca/a>universe-review.cabr />
universe-review.caa href="universe-review.ca#fungi/default.htm#fungi/">Fungiuniverse-review.ca/a>universe-review.cabr />
universe-review.caa href="universe-review.ca#gamete/default.htm#gamete/">Gameteuniverse-review.ca/a>universe-review.cabr />
universe-review.caa href="universe-review.ca#gametophyte/default.htm#gametophyte/">Gametophyteuniverse-review.ca/a>universe-review.cabr />
universe-review.caa href="universe-review.ca#germcells/default.htm#germcells/">Germ cellsuniverse-review.ca/a>universe-review.cabr />
universe-review.ca/td>universe-review.catd width="2%"> universe-review.ca/td>universe-review.catd width="49%">
universe-review.caa href="universe-review.ca#haploid/default.htm#haploid/">Haploiduniverse-review.ca/a>universe-review.cabr />
universe-review.caa href="universe-review.ca#blood/default.htm#blood/">Hemocoelic (blood) spaceuniverse-review.ca/a>universe-review.cabr />
universe-review.caa href="universe-review.ca#Hoxgenes/default.htm#Hoxgenes/">Homeobox genesuniverse-review.ca/a>universe-review.cabr />
universe-review.caa href="R10-19-animals.htm#Homo">Homo Sapiens Sapiensuniverse-review.ca/a>universe-review.cabr />
universe-review.caa href="universe-review.ca#homeodomain/default.htm#homeodomain/">Homeodomainuniverse-review.ca/a>universe-review.cabr />
universe-review.caa href="universe-review.ca#organ/default.htm#organ/">Human organ systemsuniverse-review.ca/a>universe-review.cabr />
universe-review.caa href="universe-review.ca#immortal/default.htm#immortal/">Immortaluniverse-review.ca/a>universe-review.cabr />
universe-review.caa href="R10-19-animals.htm#Jurassic">Jurassic Perioduniverse-review.ca/a>universe-review.cabr />
universe-review.caa href="R10-19-animals.htm#K-T">K-T Boundaryuniverse-review.ca/a>universe-review.cabr />
universe-review.caa href="universe-review.ca#meditation/default.htm#meditation/">Meditationuniverse-review.ca/a>universe-review.cabr />
universe-review.caa href="universe-review.ca#meiosis/default.htm#meiosis/">Meiosisuniverse-review.ca/a>universe-review.cabr />
universe-review.caa href="universe-review.ca#germlayers/default.htm#germlayers/">Mesodermuniverse-review.ca/a>universe-review.cabr />
universe-review.caa href="universe-review.ca#micronucleus/default.htm#micronucleus/">Micronucleusuniverse-review.ca/a>universe-review.cabr />
universe-review.caa href="universe-review.ca#mitosis/default.htm#mitosis/">Mitosisuniverse-review.ca/a>universe-review.cabr />
universe-review.caa href="universe-review.ca#multicellurity/default.htm#multicellurity/">Multicellurityuniverse-review.ca/a>universe-review.cabr />
universe-review.caa href="universe-review.ca#multipotent/default.htm#multipotent/">Multipotent cellsuniverse-review.ca/a>universe-review.cabr />
universe-review.caa href="universe-review.ca#neurons/default.htm#neurons/">Neuronsuniverse-review.ca/a>universe-review.cabr />
universe-review.caa href="R10-19-animals.htm#Ordovician">Ordovician Perioduniverse-review.ca/a>universe-review.cabr />
universe-review.caa href="R10-19-animals.htm#Permian">Permian Perioduniverse-review.ca/a>universe-review.cabr />
universe-review.caa href="universe-review.ca#plants/default.htm#plants/">Plantsuniverse-review.ca/a>universe-review.cabr />
universe-review.caa href="universe-review.ca#pluripotent/default.htm#pluripotent/">Pluripotent cellsuniverse-review.ca/a>universe-review.cabr />
universe-review.caa href="universe-review.ca#prokaryotes/default.htm#prokaryotes/">Prokaryotesuniverse-review.ca/a>universe-review.cabr />
universe-review.caa href="universe-review.ca#protista/default.htm#protista/">Protistauniverse-review.ca/a>universe-review.cabr />
universe-review.caa href="R10-18-slimemoulds.htm#pseudoplasmodium">Pseudoplasmodiumuniverse-review.ca/a>universe-review.cabr />
universe-review.caa href="R10-19-animals.htm#Quaternary">Quaternary Perioduniverse-review.ca/a>universe-review.cabr />
universe-review.caa href="universe-review.ca#retinoic/default.htm#retinoic/">Retinoic aciduniverse-review.ca/a>universe-review.cabr />
universe-review.caa href="universe-review.ca#sexanddeath/default.htm#sexanddeath/">Sex and deathuniverse-review.ca/a>universe-review.cabr />
universe-review.caa href="universe-review.ca#lifecycles/default.htm#lifecycles/">Sexual life cyclesuniverse-review.ca/a>universe-review.cabr />
universe-review.caa href="R10-19-animals.htm#Silurian">Silurian Perioduniverse-review.ca/a>universe-review.cabr />
universe-review.caa href="universe-review.ca#sleep/default.htm#sleep/">Sleepuniverse-review.ca/a>universe-review.cabr />
universe-review.caa href="R10-18-slimemoulds.htm">Slime mouldsuniverse-review.ca/a>universe-review.cabr />
universe-review.caa href="universe-review.ca#somatic cells/default.htm#somatic cells/">Somatic cellsuniverse-review.ca/a>universe-review.cabr />
universe-review.caa href="R10-18-slimemoulds.htm#sorocarp">Sorocarpuniverse-review.ca/a>universe-review.cabr />
universe-review.caa href="universe-review.ca#spores/default.htm#spores/">Sporesuniverse-review.ca/a>universe-review.cabr />
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