8.1: Origins of Life - Biology

8.1: Origins of Life - Biology

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8.1: Origins of Life

8.1: Origins of Life - Biology

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8.1: Origins of Life - Biology

Resource Type: Web Activity

The Cambrian Explosion Watch an animation of creatures of the Cambrian explosion created for Evolution: "Great Transformations."

Resource Type: Video
Length: 24 sec

Genetic Tool Kit The shared set of genes for body segments, possessed by all animals, are discussed in this video segment from Evolution: "Great Transformations."

Resource Type: Video
Length: 4 min, 47 sec

The Rise of Mammals
This diagram shows the enormous increase in the variety of mammals since the Cretaceous period.

Mike Novacek: Fossils in the Gobi
Biologist Mike Novacek discusses his discovery of mammal fossils in the Gobi Desert and what we can learn from them.

Biology and Evolutionary Theory
This collection of articles and essays offers scientific responses to the many questions and rebuttals that have appeared in Talk.Origins, a Usenet newsgroup devoted to the discussion and debate of biological and physical origins. Hosted by Talk.Origins.

Choose from a categorized collection of links concerning evolution. The page is hosted by a knowledgeable "guide," who screens content available on the Web for relevance and quality. Hosted by

The Tree of Life
This is University of Arizona professor David Maddison's online version of the "tree of life." With more than 2,000 Web pages contributed by research biologists worldwide, this site contains information about the diversity of organisms on Earth, their histories, and their relationships to one another.

Evolution! Facts and Fallacies
This volume contains proceedings of the "Evolution! Facts and Fallacies" symposium held at UCLA in 1997. With contributions from Schopf, Stephen Jay Gould, Charles Marshall, and others, the book addresses misconceptions of evolution and of science in general. Edited by J. William Schopf [San Diego: Academic Press, 1999].

Exploring Evolutionary Biology: Readings from American Scientist
This collection of articles written for a wide audience includes several pieces on what scientists have interpreted from the fossil record, such as when life invaded land and how it evolved once there. Edited by Montgomery Slatkin [Sunderland, Mass.: Sinauer Associates, Inc., 1995].

History of Life, 3rd ed.
Originally written for the History of Life class the author teaches at University of California, Davis, this illustrated book is an introduction to paleontology and to scientific thought in general. By Richard Cowen [Malden, Mass.: Blackwell Science, 2000].

In Search of Deep Time: Beyond the Fossil Record to a New History of Life
This book, written by the chief science writer for Nature magazine, offers offers a good introduction for readers interested in the system of classification known as cladistics. By Henry Gee [New York: The Free Press, 1999].

Patterns in Evolution: The New Molecular View
In this book, Lewin, a science journalist, explains how recently developed molecular techniques have provided a new line of evidence for evolutionary studies. By Roger Lewin [New York: Scientific American Library, 1997].

Shapes of Time: The Evolution of Growth and Development
In this book, the author details how changes in the sizes, shapes, and behaviors of certain species occur. By Kenneth J. McNamara [Baltimore: The Johns Hopkins University Press, 1997].

The Book of Life
This book, which chronologically surveys evolution, includes submissions from renowned experts Jack Sepkoski, Michael Benton, and others. Dynamic illustrations and graphs complement the strong writing. The book will appeal to students and general readers wanting an in-depth review of the history of life. Edited by Stephen Jay Gould [New York: W.W. Norton & Co., 2001].

The Fossils of the Burgess Shale
This book provides a complete picture of the renowned Burgess Shale fossil find. The authors offer detailed accounts of the fieldwork done at the site and numerous photographs and illustrations of the fossils themselves. By Derek Briggs, Douglas Erwin, and Frederick Collier [Washington, D.C.: Smithsonian Institution Press, 1994].

The Origins of Life: From the Birth of Life to the Origin of Language
In this book, two scientists update their classic work, The Major Transitions in Evolution, for a wider audience. They focus primarily on the increasingly intricate mechanisms by which life's information has been passed from generation to generation -- from life's tiny origins to the formation of cooperative societies and the birth of language. By John Maynard and Eörs Szathmáry [Oxford: Oxford University Press, 1999].


Pre-Darwinian theories

Several philosophers of the classical era, including Empedocles [1] and his intellectual successor, the Roman poet Lucretius, [2] expressed the idea that nature produces a huge variety of creatures, randomly, and that only those creatures that manage to provide for themselves and reproduce successfully persist. Empedocles' idea that organisms arose entirely by the incidental workings of causes such as heat and cold was criticised by Aristotle in Book II of Physics. [3] He posited natural teleology in its place, and believed that form was achieved for a purpose, citing the regularity of heredity in species as proof. [4] [5] Nevertheless, he accepted in his biology that new types of animals, monstrosities (τερας), can occur in very rare instances (Generation of Animals, Book IV). [6] As quoted in Darwin's 1872 edition of The Origin of Species, Aristotle considered whether different forms (e.g., of teeth) might have appeared accidentally, but only the useful forms survived:

So what hinders the different parts [of the body] from having this merely accidental relation in nature? as the teeth, for example, grow by necessity, the front ones sharp, adapted for dividing, and the grinders flat, and serviceable for masticating the food since they were not made for the sake of this, but it was the result of accident. And in like manner as to the other parts in which there appears to exist an adaptation to an end. Wheresoever, therefore, all things together (that is all the parts of one whole) happened like as if they were made for the sake of something, these were preserved, having been appropriately constituted by an internal spontaneity, and whatsoever things were not thus constituted, perished, and still perish.

But Aristotle rejected this possibility in the next paragraph, making clear that he is talking about the development of animals as embryos with the phrase "either invariably or normally come about", not the origin of species:

. Yet it is impossible that this should be the true view. For teeth and all other natural things either invariably or normally come about in a given way but of not one of the results of chance or spontaneity is this true. We do not ascribe to chance or mere coincidence the frequency of rain in winter, but frequent rain in summer we do nor heat in the dog-days, but only if we have it in winter. If then, it is agreed that things are either the result of coincidence or for an end, and these cannot be the result of coincidence or spontaneity, it follows that they must be for an end and that such things are all due to nature even the champions of the theory which is before us would agree. Therefore action for an end is present in things which come to be and are by nature.

The struggle for existence was later described by the Islamic writer Al-Jahiz in the 9th century. [9] [10] [11]

The classical arguments were reintroduced in the 18th century by Pierre Louis Maupertuis [12] and others, including Darwin's grandfather, Erasmus Darwin.

Until the early 19th century, the prevailing view in Western societies was that differences between individuals of a species were uninteresting departures from their Platonic ideals (or typus) of created kinds. However, the theory of uniformitarianism in geology promoted the idea that simple, weak forces could act continuously over long periods of time to produce radical changes in the Earth's landscape. The success of this theory raised awareness of the vast scale of geological time and made plausible the idea that tiny, virtually imperceptible changes in successive generations could produce consequences on the scale of differences between species. [13]

The early 19th-century zoologist Jean-Baptiste Lamarck suggested the inheritance of acquired characteristics as a mechanism for evolutionary change adaptive traits acquired by an organism during its lifetime could be inherited by that organism's progeny, eventually causing transmutation of species. [14] This theory, Lamarckism, was an influence on the Soviet biologist Trofim Lysenko's antagonism to mainstream genetic theory as late as the mid 20th century. [15]

Between 1835 and 1837, the zoologist Edward Blyth worked on the area of variation, artificial selection, and how a similar process occurs in nature. Darwin acknowledged Blyth's ideas in the first chapter on variation of On the Origin of Species. [16]

Darwin's theory

In 1859, Charles Darwin set out his theory of evolution by natural selection as an explanation for adaptation and speciation. He defined natural selection as the "principle by which each slight variation [of a trait], if useful, is preserved". [17] The concept was simple but powerful: individuals best adapted to their environments are more likely to survive and reproduce. As long as there is some variation between them and that variation is heritable, there will be an inevitable selection of individuals with the most advantageous variations. If the variations are heritable, then differential reproductive success leads to a progressive evolution of particular populations of a species, and populations that evolve to be sufficiently different eventually become different species. [18] [19]

Darwin's ideas were inspired by the observations that he had made on the second voyage of HMS Beagle (1831–1836), and by the work of a political economist, Thomas Robert Malthus, who, in An Essay on the Principle of Population (1798), noted that population (if unchecked) increases exponentially, whereas the food supply grows only arithmetically thus, inevitable limitations of resources would have demographic implications, leading to a "struggle for existence". [20] When Darwin read Malthus in 1838 he was already primed by his work as a naturalist to appreciate the "struggle for existence" in nature. It struck him that as population outgrew resources, "favourable variations would tend to be preserved, and unfavourable ones to be destroyed. The result of this would be the formation of new species." [21] Darwin wrote:

If during the long course of ages and under varying conditions of life, organic beings vary at all in the several parts of their organisation, and I think this cannot be disputed if there be, owing to the high geometrical powers of increase of each species, at some age, season, or year, a severe struggle for life, and this certainly cannot be disputed then, considering the infinite complexity of the relations of all organic beings to each other and to their conditions of existence, causing an infinite diversity in structure, constitution, and habits, to be advantageous to them, I think it would be a most extraordinary fact if no variation ever had occurred useful to each being's own welfare, in the same way as so many variations have occurred useful to man. But if variations useful to any organic being do occur, assuredly individuals thus characterised will have the best chance of being preserved in the struggle for life and from the strong principle of inheritance they will tend to produce offspring similarly characterised. This principle of preservation, I have called, for the sake of brevity, Natural Selection.

Once he had his theory, Darwin was meticulous about gathering and refining evidence before making his idea public. He was in the process of writing his "big book" to present his research when the naturalist Alfred Russel Wallace independently conceived of the principle and described it in an essay he sent to Darwin to forward to Charles Lyell. Lyell and Joseph Dalton Hooker decided to present his essay together with unpublished writings that Darwin had sent to fellow naturalists, and On the Tendency of Species to form Varieties and on the Perpetuation of Varieties and Species by Natural Means of Selection was read to the Linnean Society of London announcing co-discovery of the principle in July 1858. [23] Darwin published a detailed account of his evidence and conclusions in On the Origin of Species in 1859. In the 3rd edition of 1861 Darwin acknowledged that others—like William Charles Wells in 1813, and Patrick Matthew in 1831—had proposed similar ideas, but had neither developed them nor presented them in notable scientific publications. [24]

Darwin thought of natural selection by analogy to how farmers select crops or livestock for breeding, which he called "artificial selection" in his early manuscripts he referred to a "Nature" which would do the selection. At the time, other mechanisms of evolution such as evolution by genetic drift were not yet explicitly formulated, and Darwin believed that selection was likely only part of the story: "I am convinced that Natural Selection has been the main but not exclusive means of modification." [25] In a letter to Charles Lyell in September 1860, Darwin regretted the use of the term "Natural Selection", preferring the term "Natural Preservation". [26]

For Darwin and his contemporaries, natural selection was in essence synonymous with evolution by natural selection. After the publication of On the Origin of Species, [27] educated people generally accepted that evolution had occurred in some form. However, natural selection remained controversial as a mechanism, partly because it was perceived to be too weak to explain the range of observed characteristics of living organisms, and partly because even supporters of evolution balked at its "unguided" and non-progressive nature, [28] a response that has been characterised as the single most significant impediment to the idea's acceptance. [29] However, some thinkers enthusiastically embraced natural selection after reading Darwin, Herbert Spencer introduced the phrase survival of the fittest, which became a popular summary of the theory. [30] [31] The fifth edition of On the Origin of Species published in 1869 included Spencer's phrase as an alternative to natural selection, with credit given: "But the expression often used by Mr. Herbert Spencer of the Survival of the Fittest is more accurate, and is sometimes equally convenient." [32] Although the phrase is still often used by non-biologists, modern biologists avoid it because it is tautological if "fittest" is read to mean "functionally superior" and is applied to individuals rather than considered as an averaged quantity over populations. [33]

The modern synthesis

Natural selection relies crucially on the idea of heredity, but developed before the basic concepts of genetics. Although the Moravian monk Gregor Mendel, the father of modern genetics, was a contemporary of Darwin's, his work lay in obscurity, only being rediscovered in 1900. [34] With the early 20th century integration of evolution with Mendel's laws of inheritance, the so-called modern synthesis, scientists generally came to accept natural selection. [35] [36] The synthesis grew from advances in different fields. Ronald Fisher developed the required mathematical language and wrote The Genetical Theory of Natural Selection (1930). [37] J. B. S. Haldane introduced the concept of the "cost" of natural selection. [38] [39] Sewall Wright elucidated the nature of selection and adaptation. [40] In his book Genetics and the Origin of Species (1937), Theodosius Dobzhansky established the idea that mutation, once seen as a rival to selection, actually supplied the raw material for natural selection by creating genetic diversity. [41] [42]

A second synthesis

Ernst Mayr recognised the key importance of reproductive isolation for speciation in his Systematics and the Origin of Species (1942). [44] W. D. Hamilton conceived of kin selection in 1964. [45] [46] This synthesis cemented natural selection as the foundation of evolutionary theory, where it remains today. A second synthesis was brought about at the end of the 20th century by advances in molecular genetics, creating the field of evolutionary developmental biology ("evo-devo"), which seeks to explain the evolution of form in terms of the genetic regulatory programs which control the development of the embryo at molecular level. Natural selection is here understood to act on embryonic development to change the morphology of the adult body. [47] [48] [49] [50]

The term natural selection is most often defined to operate on heritable traits, because these directly participate in evolution. However, natural selection is "blind" in the sense that changes in phenotype can give a reproductive advantage regardless of whether or not the trait is heritable. Following Darwin's primary usage, the term is used to refer both to the evolutionary consequence of blind selection and to its mechanisms. [27] [37] [51] [52] It is sometimes helpful to explicitly distinguish between selection's mechanisms and its effects when this distinction is important, scientists define "(phenotypic) natural selection" specifically as "those mechanisms that contribute to the selection of individuals that reproduce", without regard to whether the basis of the selection is heritable. [53] [54] [55] Traits that cause greater reproductive success of an organism are said to be selected for, while those that reduce success are selected against. [56]

Heritable variation, differential reproduction

Natural variation occurs among the individuals of any population of organisms. Some differences may improve an individual's chances of surviving and reproducing such that its lifetime reproductive rate is increased, which means that it leaves more offspring. If the traits that give these individuals a reproductive advantage are also heritable, that is, passed from parent to offspring, then there will be differential reproduction, that is, a slightly higher proportion of fast rabbits or efficient algae in the next generation. Even if the reproductive advantage is very slight, over many generations any advantageous heritable trait becomes dominant in the population. In this way the natural environment of an organism "selects for" traits that confer a reproductive advantage, causing evolutionary change, as Darwin described. [57] This gives the appearance of purpose, but in natural selection there is no intentional choice. [a] Artificial selection is purposive where natural selection is not, though biologists often use teleological language to describe it. [58]

The peppered moth exists in both light and dark colours in Great Britain, but during the industrial revolution, many of the trees on which the moths rested became blackened by soot, giving the dark-coloured moths an advantage in hiding from predators. This gave dark-coloured moths a better chance of surviving to produce dark-coloured offspring, and in just fifty years from the first dark moth being caught, nearly all of the moths in industrial Manchester were dark. The balance was reversed by the effect of the Clean Air Act 1956, and the dark moths became rare again, demonstrating the influence of natural selection on peppered moth evolution. [59] A recent study, using image analysis and avian vision models, shows that pale individuals more closely match lichen backgrounds than dark morphs and for the first time quantifies the camouflage of moths to predation risk. [60]


The concept of fitness is central to natural selection. In broad terms, individuals that are more "fit" have better potential for survival, as in the well-known phrase "survival of the fittest", but the precise meaning of the term is much more subtle. Modern evolutionary theory defines fitness not by how long an organism lives, but by how successful it is at reproducing. If an organism lives half as long as others of its species, but has twice as many offspring surviving to adulthood, its genes become more common in the adult population of the next generation. Though natural selection acts on individuals, the effects of chance mean that fitness can only really be defined "on average" for the individuals within a population. The fitness of a particular genotype corresponds to the average effect on all individuals with that genotype. [61] A distinction must be made between the concept of "survival of the fittest" and "improvement in fitness". "Survival of the fittest" does not give an "improvement in fitness", it only represents the removal of the less fit variants from a population. A mathematical example of "survival of the fittest" is given by Haldane in his paper "The Cost of Natural Selection". [62] Haldane called this process "substitution" or more commonly in biology, this is called "fixation". This is correctly described by the differential survival and reproduction of individuals due to differences in phenotype. On the other hand, "improvement in fitness" is not dependent on the differential survival and reproduction of individuals due to differences in phenotype, it is dependent on the absolute survival of the particular variant. The probability of a beneficial mutation occurring on some member of a population depends on the total number of replications of that variant. The mathematics of "improvement in fitness was described by Kleinman. [63] An empirical example of "improvement in fitness" is given by the Kishony Mega-plate experiment. [64] In this experiment, "improvement in fitness" depends on the number of replications of the particular variant for a new variant to appear that is capable of growing in the next higher drug concentration region. Fixation or substitution is not required for this "improvement in fitness". On the other hand, "improvement in fitness" can occur in an environment where "survival of the fittest" is also acting. Richard Lenski's classic E. coli long-term evolution experiment is an example of adaptation in a competitive environment, ("improvement in fitness" during "survival of the fittest"). [65] The probability of a beneficial mutation occurring on some member of the lineage to give improved fitness is slowed by the competition. The variant which is a candidate for a beneficial mutation in this limited carrying capacity environment must first out-compete the "less fit" variants in order to accumulate the requisite number of replications for there to be a reasonable probability of that beneficial mutation occurring. [66]


In biology, competition is an interaction between organisms in which the fitness of one is lowered by the presence of another. This may be because both rely on a limited supply of a resource such as food, water, or territory. [67] Competition may be within or between species, and may be direct or indirect. [68] Species less suited to compete should in theory either adapt or die out, since competition plays a powerful role in natural selection, but according to the "room to roam" theory it may be less important than expansion among larger clades. [68] [69]

Competition is modelled by r/K selection theory, which is based on Robert MacArthur and E. O. Wilson's work on island biogeography. [70] In this theory, selective pressures drive evolution in one of two stereotyped directions: r- or K-selection. [71] These terms, r and K, can be illustrated in a logistic model of population dynamics: [72]

where r is the growth rate of the population (N), and K is the carrying capacity of its local environmental setting. Typically, r-selected species exploit empty niches, and produce many offspring, each with a relatively low probability of surviving to adulthood. In contrast, K-selected species are strong competitors in crowded niches, and invest more heavily in much fewer offspring, each with a relatively high probability of surviving to adulthood. [72]

Natural selection can act on any heritable phenotypic trait, [73] and selective pressure can be produced by any aspect of the environment, including sexual selection and competition with members of the same or other species. [74] [75] However, this does not imply that natural selection is always directional and results in adaptive evolution natural selection often results in the maintenance of the status quo by eliminating less fit variants. [57]

Selection can be classified in several different ways, such as by its effect on a trait, on genetic diversity, by the life cycle stage where it acts, by the unit of selection, or by the resource being competed for.

By effect on a trait

Selection has different effects on traits. Stabilizing selection acts to hold a trait at a stable optimum, and in the simplest case all deviations from this optimum are selectively disadvantageous. Directional selection favours extreme values of a trait. The uncommon disruptive selection also acts during transition periods when the current mode is sub-optimal, but alters the trait in more than one direction. In particular, if the trait is quantitative and univariate then both higher and lower trait levels are favoured. Disruptive selection can be a precursor to speciation. [57]

By effect on genetic diversity

Alternatively, selection can be divided according to its effect on genetic diversity. Purifying or negative selection acts to remove genetic variation from the population (and is opposed by de novo mutation, which introduces new variation. [76] [77] In contrast, balancing selection acts to maintain genetic variation in a population, even in the absence of de novo mutation, by negative frequency-dependent selection. One mechanism for this is heterozygote advantage, where individuals with two different alleles have a selective advantage over individuals with just one allele. The polymorphism at the human ABO blood group locus has been explained in this way. [78]

By life cycle stage

Another option is to classify selection by the life cycle stage at which it acts. Some biologists recognise just two types: viability (or survival) selection, which acts to increase an organism's probability of survival, and fecundity (or fertility or reproductive) selection, which acts to increase the rate of reproduction, given survival. Others split the life cycle into further components of selection. Thus viability and survival selection may be defined separately and respectively as acting to improve the probability of survival before and after reproductive age is reached, while fecundity selection may be split into additional sub-components including sexual selection, gametic selection, acting on gamete survival, and compatibility selection, acting on zygote formation. [79]

By unit of selection

Selection can also be classified by the level or unit of selection. Individual selection acts on the individual, in the sense that adaptations are "for" the benefit of the individual, and result from selection among individuals. Gene selection acts directly at the level of the gene. In kin selection and intragenomic conflict, gene-level selection provides a more apt explanation of the underlying process. Group selection, if it occurs, acts on groups of organisms, on the assumption that groups replicate and mutate in an analogous way to genes and individuals. There is an ongoing debate over the degree to which group selection occurs in nature. [80]

By resource being competed for

Finally, selection can be classified according to the resource being competed for. Sexual selection results from competition for mates. Sexual selection typically proceeds via fecundity selection, sometimes at the expense of viability. Ecological selection is natural selection via any means other than sexual selection, such as kin selection, competition, and infanticide. Following Darwin, natural selection is sometimes defined as ecological selection, in which case sexual selection is considered a separate mechanism. [83]

Sexual selection as first articulated by Darwin (using the example of the peacock's tail) [81] refers specifically to competition for mates, [84] which can be intrasexual, between individuals of the same sex, that is male–male competition, or intersexual, where one gender chooses mates, most often with males displaying and females choosing. [85] However, in some species, mate choice is primarily by males, as in some fishes of the family Syngnathidae. [86] [87]

Phenotypic traits can be displayed in one sex and desired in the other sex, causing a positive feedback loop called a Fisherian runaway, for example, the extravagant plumage of some male birds such as the peacock. [82] An alternate theory proposed by the same Ronald Fisher in 1930 is the sexy son hypothesis, that mothers want promiscuous sons to give them large numbers of grandchildren and so choose promiscuous fathers for their children. Aggression between members of the same sex is sometimes associated with very distinctive features, such as the antlers of stags, which are used in combat with other stags. More generally, intrasexual selection is often associated with sexual dimorphism, including differences in body size between males and females of a species. [85]

Natural selection is seen in action in the development of antibiotic resistance in microorganisms. Since the discovery of penicillin in 1928, antibiotics have been used to fight bacterial diseases. The widespread misuse of antibiotics has selected for microbial resistance to antibiotics in clinical use, to the point that the methicillin-resistant Staphylococcus aureus (MRSA) has been described as a "superbug" because of the threat it poses to health and its relative invulnerability to existing drugs. [88] Response strategies typically include the use of different, stronger antibiotics however, new strains of MRSA have recently emerged that are resistant even to these drugs. [89] This is an evolutionary arms race, in which bacteria develop strains less susceptible to antibiotics, while medical researchers attempt to develop new antibiotics that can kill them. A similar situation occurs with pesticide resistance in plants and insects. Arms races are not necessarily induced by man a well-documented example involves the spread of a gene in the butterfly Hypolimnas bolina suppressing male-killing activity by Wolbachia bacteria parasites on the island of Samoa, where the spread of the gene is known to have occurred over a period of just five years [90] [91]

A prerequisite for natural selection to result in adaptive evolution, novel traits and speciation is the presence of heritable genetic variation that results in fitness differences. Genetic variation is the result of mutations, genetic recombinations and alterations in the karyotype (the number, shape, size and internal arrangement of the chromosomes). Any of these changes might have an effect that is highly advantageous or highly disadvantageous, but large effects are rare. In the past, most changes in the genetic material were considered neutral or close to neutral because they occurred in noncoding DNA or resulted in a synonymous substitution. However, many mutations in non-coding DNA have deleterious effects. [92] [93] Although both mutation rates and average fitness effects of mutations are dependent on the organism, a majority of mutations in humans are slightly deleterious. [94]

Some mutations occur in "toolkit" or regulatory genes. Changes in these often have large effects on the phenotype of the individual because they regulate the function of many other genes. Most, but not all, mutations in regulatory genes result in non-viable embryos. Some nonlethal regulatory mutations occur in HOX genes in humans, which can result in a cervical rib [95] or polydactyly, an increase in the number of fingers or toes. [96] When such mutations result in a higher fitness, natural selection favours these phenotypes and the novel trait spreads in the population. Established traits are not immutable traits that have high fitness in one environmental context may be much less fit if environmental conditions change. In the absence of natural selection to preserve such a trait, it becomes more variable and deteriorate over time, possibly resulting in a vestigial manifestation of the trait, also called evolutionary baggage. In many circumstances, the apparently vestigial structure may retain a limited functionality, or may be co-opted for other advantageous traits in a phenomenon known as preadaptation. A famous example of a vestigial structure, the eye of the blind mole-rat, is believed to retain function in photoperiod perception. [97]


Speciation requires a degree of reproductive isolation—that is, a reduction in gene flow. However, it is intrinsic to the concept of a species that hybrids are selected against, opposing the evolution of reproductive isolation, a problem that was recognised by Darwin. The problem does not occur in allopatric speciation with geographically separated populations, which can diverge with different sets of mutations. E. B. Poulton realized in 1903 that reproductive isolation could evolve through divergence, if each lineage acquired a different, incompatible allele of the same gene. Selection against the heterozygote would then directly create reproductive isolation, leading to the Bateson–Dobzhansky–Muller model, further elaborated by H. Allen Orr [98] and Sergey Gavrilets. [99] With reinforcement, however, natural selection can favor an increase in pre-zygotic isolation, influencing the process of speciation directly. [100]

Genotype and phenotype

Natural selection acts on an organism's phenotype, or physical characteristics. Phenotype is determined by an organism's genetic make-up (genotype) and the environment in which the organism lives. When different organisms in a population possess different versions of a gene for a certain trait, each of these versions is known as an allele. It is this genetic variation that underlies differences in phenotype. An example is the ABO blood type antigens in humans, where three alleles govern the phenotype. [101]

Some traits are governed by only a single gene, but most traits are influenced by the interactions of many genes. A variation in one of the many genes that contributes to a trait may have only a small effect on the phenotype together, these genes can produce a continuum of possible phenotypic values. [102]

Directionality of selection

When some component of a trait is heritable, selection alters the frequencies of the different alleles, or variants of the gene that produces the variants of the trait. Selection can be divided into three classes, on the basis of its effect on allele frequencies: directional, stabilizing, and disruptive selection. [103] Directional selection occurs when an allele has a greater fitness than others, so that it increases in frequency, gaining an increasing share in the population. This process can continue until the allele is fixed and the entire population shares the fitter phenotype. [104] Far more common is stabilizing selection, which lowers the frequency of alleles that have a deleterious effect on the phenotype—that is, produce organisms of lower fitness. This process can continue until the allele is eliminated from the population. Stabilizing selection conserves functional genetic features, such as protein-coding genes or regulatory sequences, over time by selective pressure against deleterious variants. [105] Disruptive (or diversifying) selection is selection favoring extreme trait values over intermediate trait values. Disruptive selection may cause sympatric speciation through niche partitioning.

Some forms of balancing selection do not result in fixation, but maintain an allele at intermediate frequencies in a population. This can occur in diploid species (with pairs of chromosomes) when heterozygous individuals (with just one copy of the allele) have a higher fitness than homozygous individuals (with two copies). This is called heterozygote advantage or over-dominance, of which the best-known example is the resistance to malaria in humans heterozygous for sickle-cell anaemia. Maintenance of allelic variation can also occur through disruptive or diversifying selection, which favours genotypes that depart from the average in either direction (that is, the opposite of over-dominance), and can result in a bimodal distribution of trait values. Finally, balancing selection can occur through frequency-dependent selection, where the fitness of one particular phenotype depends on the distribution of other phenotypes in the population. The principles of game theory have been applied to understand the fitness distributions in these situations, particularly in the study of kin selection and the evolution of reciprocal altruism. [106] [107]

Selection, genetic variation, and drift

A portion of all genetic variation is functionally neutral, producing no phenotypic effect or significant difference in fitness. Motoo Kimura's neutral theory of molecular evolution by genetic drift proposes that this variation accounts for a large fraction of observed genetic diversity. [108] Neutral events can radically reduce genetic variation through population bottlenecks. [109] which among other things can cause the founder effect in initially small new populations. [110] When genetic variation does not result in differences in fitness, selection cannot directly affect the frequency of such variation. As a result, the genetic variation at those sites is higher than at sites where variation does influence fitness. [103] However, after a period with no new mutations, the genetic variation at these sites is eliminated due to genetic drift. Natural selection reduces genetic variation by eliminating maladapted individuals, and consequently the mutations that caused the maladaptation. At the same time, new mutations occur, resulting in a mutation–selection balance. The exact outcome of the two processes depends both on the rate at which new mutations occur and on the strength of the natural selection, which is a function of how unfavourable the mutation proves to be. [111]

Genetic linkage occurs when the loci of two alleles are in close proximity on a chromosome. During the formation of gametes, recombination reshuffles the alleles. The chance that such a reshuffle occurs between two alleles is inversely related to the distance between them. Selective sweeps occur when an allele becomes more common in a population as a result of positive selection. As the prevalence of one allele increases, closely linked alleles can also become more common by "genetic hitchhiking", whether they are neutral or even slightly deleterious. A strong selective sweep results in a region of the genome where the positively selected haplotype (the allele and its neighbours) are in essence the only ones that exist in the population. Selective sweeps can be detected by measuring linkage disequilibrium, or whether a given haplotype is overrepresented in the population. Since a selective sweep also results in selection of neighbouring alleles, the presence of a block of strong linkage disequilibrium might indicate a 'recent' selective sweep near the centre of the block. [112]

Background selection is the opposite of a selective sweep. If a specific site experiences strong and persistent purifying selection, linked variation tends to be weeded out along with it, producing a region in the genome of low overall variability. Because background selection is a result of deleterious new mutations, which can occur randomly in any haplotype, it does not produce clear blocks of linkage disequilibrium, although with low recombination it can still lead to slightly negative linkage disequilibrium overall. [113]

Darwin's ideas, along with those of Adam Smith and Karl Marx, had a profound influence on 19th century thought, including his radical claim that "elaborately constructed forms, so different from each other, and dependent on each other in so complex a manner" evolved from the simplest forms of life by a few simple principles. [114] This inspired some of Darwin's most ardent supporters—and provoked the strongest opposition. Natural selection had the power, according to Stephen Jay Gould, to "dethrone some of the deepest and most traditional comforts of Western thought", such as the belief that humans have a special place in the world. [115]

In the words of the philosopher Daniel Dennett, "Darwin's dangerous idea" of evolution by natural selection is a "universal acid," which cannot be kept restricted to any vessel or container, as it soon leaks out, working its way into ever-wider surroundings. [116] Thus, in the last decades, the concept of natural selection has spread from evolutionary biology to other disciplines, including evolutionary computation, quantum Darwinism, evolutionary economics, evolutionary epistemology, evolutionary psychology, and cosmological natural selection. This unlimited applicability has been called universal Darwinism. [117]

Origin of life

How life originated from inorganic matter remains an unresolved problem in biology. One prominent hypothesis is that life first appeared in the form of short self-replicating RNA polymers. [118] On this view, life may have come into existence when RNA chains first experienced the basic conditions, as conceived by Charles Darwin, for natural selection to operate. These conditions are: heritability, variation of type, and competition for limited resources. The fitness of an early RNA replicator would likely have been a function of adaptive capacities that were intrinsic (i.e., determined by the nucleotide sequence) and the availability of resources. [119] [120] The three primary adaptive capacities could logically have been: (1) the capacity to replicate with moderate fidelity (giving rise to both heritability and variation of type), (2) the capacity to avoid decay, and (3) the capacity to acquire and process resources. [119] [120] These capacities would have been determined initially by the folded configurations (including those configurations with ribozyme activity) of the RNA replicators that, in turn, would have been encoded in their individual nucleotide sequences. [121]

Cell and molecular biology

In 1881, the embryologist Wilhelm Roux published Der Kampf der Theile im Organismus (The Struggle of Parts in the Organism) in which he suggested that the development of an organism results from a Darwinian competition between the parts of the embryo, occurring at all levels, from molecules to organs. [122] In recent years, a modern version of this theory has been proposed by Jean-Jacques Kupiec. According to this cellular Darwinism, random variation at the molecular level generates diversity in cell types whereas cell interactions impose a characteristic order on the developing embryo. [123]

Social and psychological theory

The social implications of the theory of evolution by natural selection also became the source of continuing controversy. Friedrich Engels, a German political philosopher and co-originator of the ideology of communism, wrote in 1872 that "Darwin did not know what a bitter satire he wrote on mankind, and especially on his countrymen, when he showed that free competition, the struggle for existence, which the economists celebrate as the highest historical achievement, is the normal state of the animal kingdom." [124] Herbert Spencer and the eugenics advocate Francis Galton's interpretation of natural selection as necessarily progressive, leading to supposed advances in intelligence and civilisation, became a justification for colonialism, eugenics, and social Darwinism. For example, in 1940, Konrad Lorenz, in writings that he subsequently disowned, used the theory as a justification for policies of the Nazi state. He wrote ". selection for toughness, heroism, and social utility . must be accomplished by some human institution, if mankind, in default of selective factors, is not to be ruined by domestication-induced degeneracy. The racial idea as the basis of our state has already accomplished much in this respect." [125] Others have developed ideas that human societies and culture evolve by mechanisms analogous to those that apply to evolution of species. [126]

More recently, work among anthropologists and psychologists has led to the development of sociobiology and later of evolutionary psychology, a field that attempts to explain features of human psychology in terms of adaptation to the ancestral environment. The most prominent example of evolutionary psychology, notably advanced in the early work of Noam Chomsky and later by Steven Pinker, is the hypothesis that the human brain has adapted to acquire the grammatical rules of natural language. [127] Other aspects of human behaviour and social structures, from specific cultural norms such as incest avoidance to broader patterns such as gender roles, have been hypothesised to have similar origins as adaptations to the early environment in which modern humans evolved. By analogy to the action of natural selection on genes, the concept of memes—"units of cultural transmission," or culture's equivalents of genes undergoing selection and recombination—has arisen, first described in this form by Richard Dawkins in 1976 [128] and subsequently expanded upon by philosophers such as Daniel Dennett as explanations for complex cultural activities, including human consciousness. [129]

Information and systems theory

In 1922, Alfred J. Lotka proposed that natural selection might be understood as a physical principle that could be described in terms of the use of energy by a system, [130] [131] a concept later developed by Howard T. Odum as the maximum power principle in thermodynamics, whereby evolutionary systems with selective advantage maximise the rate of useful energy transformation. [132]

The principles of natural selection have inspired a variety of computational techniques, such as "soft" artificial life, that simulate selective processes and can be highly efficient in 'adapting' entities to an environment defined by a specified fitness function. [133] For example, a class of heuristic optimisation algorithms known as genetic algorithms, pioneered by John Henry Holland in the 1970s and expanded upon by David E. Goldberg, [134] identify optimal solutions by simulated reproduction and mutation of a population of solutions defined by an initial probability distribution. [135] Such algorithms are particularly useful when applied to problems whose energy landscape is very rough or has many local minima. [136]

In fiction

Darwinian evolution by natural selection is pervasive in literature, whether taken optimistically in terms of how humanity may evolve towards perfection, or pessimistically in terms of the dire consequences of the interaction of human nature and the struggle for survival. Among major responses is Samuel Butler's 1872 pessimistic Erewhon ("nowhere", written mostly backwards). In 1893 H. G. Wells imagined "The Man of the Year Million", transformed by natural selection into a being with a huge head and eyes, and shrunken body. [137]

This course covers the complete NCERT / CBSE course based syllabus with all chapters of Class 11th Biology which has been taught topic wise. This also covers the concepts useful for competitive exams such as NEET etc.

What are the topics we are going to learn in chapter respiratory system?

1.2 Stages of Respiration 1.3 Types of Respiration 1.4 Anaerobic Respiration 1.5 Respiratory Organs (Part 1)

Characteristics of respiratory organs

2.1 Body Fluids And Circulation - Introduction 2.2 Blood (Plasma) 2.3 Blood (Erythrocytes) 2.4 Leucocytes (White Blood Corpuscles or WBCs) 2.5 Types Of WBCs 3.1 Introduction 3.2 Water and Solute Regulation in Different Environment (Part 1) 3.3 Water and Solute Regulation in Different Environment (Part 2) 3.4 Excretory Organs in Invertebrates (Part 1) 3.5 Excretory Organs in Invertebrates (Part 2) 4.1 Introduction 4.2 What Is Living 4.3 Characteristics of Living Being 4.4 Characteristics of Living Being (Reproduction) 4.5 Consciousness 5.1 Introduction 5.2 Three And Four Kingdom Systems Of Classification 5.3 Five And Six Kingdom Systems Of Classification 5.4 Kingdom Monera 5.5 Kingdom Monera (Respiration) 6.1 Animal Kingdom - Introduction 6.2 General Feature of Kingdom Animalia 6.3 Artificial System of Classification of Animals 6.4 Natural system of classification of Animals 6.5 Hierarchy of Taxonomy 7.1 Introduction 7.2 Mouth and Buccopharyngeal Cavity 7.3 Buccal Cavity-Palate, Pharynx,Tonsil 7.4 Buccal Cavity- Teeth 7.5 Buccal Cavity- Tongue 8.1 Introduction 8.2 The Human Skeletal System and it's Parts 8.3 Facial Bones (Axial Skeletal System) 8.4 Vertebral Column (Axial Skeletal System) 8.5 Sternum and Ribs (Axial Skeletal System) 9.1 Introduction 9.2 Classification of Plant Kingdom 9.3 Plant Kingdom- General Characteristics of Algae 9.4 Classification of Algae 9.5 NCERT बूटी - Plant Kingdom 10.1 Introduction 10.2 Overview of Cell 10.3 Prokaryotic Cell 10.4 Prokaryotic Cell: NCERT बूटी 10.5 Difference between Prokaryotic and Eukaryotic Cell 11.1 Mitosis 11.2 Significance of Mitosis 11.3 NCERT बूटी - Mitosis 11.4 Meiosis- 1 11.5 Meiosis- 2 12.1 Introduction 12.2 How to Analyse Chemical Composition? 12.3 Carbohydrates (part 1) 12.4 Carbohydrates (part 2) 12.5 Proteins 13.1 Introduction 13.2 Epithelial Tissues Introduction 13.3 Types Epithelial Tissues (Part -1) 13.4 Types Epithelial Tissues (Part -2) 13.5 Cell Junctions 14.1 Introduction 14.2 Glycolysis 14.3 Krebs Cycle 14.4 Electron Transport System (ETS) 14.5 Fermentation and Amphibolic Pathway 15.1 Introduction 15.2 Early Experiments (Part 1) 15.3 Early Experiments (Part 2) 15:4 Light Reaction (Part 1) 15.5 Light Reaction (Part 2) 16.1 Introduction 16.2 Means of Transport (Short Distance ) 16.3 Plant Water Relations 16.4 Water Potential 16.5 Water Potential NCERT बूटी 17.1 Introduction 17.2 Classification of Essential Elements 17.3 Role of Macro Nutrients 17.4 Micro Nutrients,deficiency Symptoms,toxicity of Minerals 17.5 Metabolism of Nitrogen 18.1 Meristematic Tissues - Introduction 18.2 Permanent Tissues 18.3 The Tissue System 18.4 Anatomy Of Root 18.5 Anatomy of Stem 19.1 Root and Its Modifications 19.2 Stem and Its Modifications 19.3 Leaf and Its Modifications 19.4 Leaf NCERT बूटी 19.5 Inflorescence 20.1 Plant Growth And Development (Lecture 1) 20.2 Plant Growth And Development (Lecture 2) 20.3 Plant Growth And Development (Lecture 3) 20.4 Plant Hormones (Auxins) 20.5 Plant Hormone (Gibberellins)

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What is Code Biology?

Codes and conventions are the basis of our social life and from time immemorial have divided the world of culture from the world of nature. The rules of grammar, the laws of government, the precepts of religion, the value of money, the rules of chess etc., are all human conventions that are profoundly different from the laws of physics and chemistry, and this has led to the conclusion that there is an unbridgeable gap between nature and culture. Nature is governed by objective immutable laws, whereas culture is produced by the mutable conventions of the human mind.

In this millennia-old framework, the discovery of the genetic code, in the early 1960s, came as a bolt from the blue, but strangely enough it did not bring down the barrier between nature and culture. On the contrary, a protective belt was quickly built around the old divide with an argument that effectively emptied the discovery of all its revolutionary potential. The argument that the genetic code is not a real code because its rules are the result of chemical affinities between codons and amino acids and are therefore determined by chemistry. This is the ‘Stereochemical theory’, an idea first proposed by George Gamow in 1954, and re-proposed ever since in many different forms (Pelc and Welton 1966 Dunnil 1966 Melcher 1974 Shimizu 1982 Yarus 1988, 1998 Yarus, Caporaso and Knight 2005). More than fifty years of research have not produced any evidence in favour of this theory and yet the idea is still circulating, apparently because of the possibility that stereochemical interactions might have been important at some early stages of evolution (Koonin and Novozhilov 2009). The deep reason is probably the persistent belief that the genetic code must have been a product of chemistry and cannot possibly be a real code. But what is a real code?

The starting point is the idea that a code is a set of rules that establish a correspondence, or a mapping, between the objects of two independent worlds (Barbieri 2003). The Morse code, for example, is a mapping between the letters of the alphabet and groups of dots and dashes. The highway code is a correspondence between street signals and driving behaviours (a red light means ‘stop’, a green light means ‘go’, and so on).

What is essential in all codes is that the coding rules, although completely compatible with the laws of physics and chemistry, are not dictated by these laws. In this sense they are arbitrary, and the number of arbitrary relationships between two independent worlds is potentially unlimited. In the Morse code, for example, any letter of the alphabet could be associated with countless combinations of dots and dashes, which means that a specific link between them can be realized only by selecting a small number of rules. And this is precisely what a code is: a small set of arbitrary rules selected from a potentially unlimited number in order to ensure a specific correspondence between two independent worlds.

This definition allows us to make experimental tests because organic codes are relationships between two worlds of organic molecules and are necessarily implemented by a third type of molecules, called adaptors, that build a bridge between them. The adaptors are required because there is no necessary link between the two worlds, and a fixed set of adaptors is required in order to guarantee the specificity of the correspondence. The adaptors, in short, are the molecular fingerprints of the codes, and their presence in a biological process is a sure sign that that process is based on a code.

This gives us an objective criterion for discovering organic codes and their existence is no longer a matter of speculation. It is, first and foremost, an experimental problem. More precisely, we can prove that an organic code exists, if we find three things: (1) two independents worlds of molecules, (2) a set of adaptors that create a mapping between them, and (3) the demonstration that the mapping is arbitrary because its rules can be changed, at least in principle, in countless different ways.

Two outstanding examples

In protein synthesis, a sequence of nucleotides is translated into a sequence of amino acids, and the bridge between them is realized by a third type of molecules, called transfer-RNAs, that act as adaptors and perform two distinct operations: at one site they recognize groups of three nucleotides, called codons, and at another site they receive amino acids from enzymes called aminoacyl-tRNA-synthetases. The key point is that there is no deterministic link between codons and amino acids since it has been shown that any codon can be associated with any amino acid (Schimmel 1987 Schimmel et al. 1993). Hou and Schimmel (1988), for example, introduced two extra nucleotides in a tRNA and found that that the resulting tRNA was carrying a different amino acid. This proved that the number of possible connections between codons and amino acids is potentially unlimited, and only the selection of a small set of adaptors can ensure a specific mapping. This is the genetic code: a fixed set of rules between nucleic acids and amino acids that are implemented by adaptors. In protein synthesis, in conclusion, we find all the three essential components of a code: (1) two independents worlds of molecules (nucleotides and amino acids), (2) a set of adaptors that create a mapping between them, and (3) the proof that the mapping is arbitrary because its rules can be changed.

The signal transduction codes

Signal transduction is the process by which cells transform the signals from the environment, called first messengers, into internal signals, called second messengers. First and second messengers belong to two independent worlds because there are literally hundreds of first messengers (hormones, growth factors, neurotransmitters, etc.) but only four great families of second messengers (cyclic AMP, calcium ions, diacylglycerol and inositol trisphosphate) (Alberts et al. 2007). The crucial point is that the molecules that perform signal transduction are true adaptors. They consists of three subunits: a receptor for the first messengers, an amplifier for the second messengers, and a mediator in between (Berridge 1985). This allows the transduction complex to perform two independent recognition processes, one for the first messenger and the other for the second messenger. Laboratory experiments have proved that any first messenger can be associated with any second messenger, which means that there is a potentially unlimited number of arbitrary connections between them. In signal transduction, in short, we find all the three essential components of a code: (1) two independents worlds of molecules (first messengers and second messengers), (2) a set of adaptors that create a mapping between them, and (3) the proof that the mapping is arbitrary because its rules can be changed (Barbieri 2003).

A world of organic codes

In addition to the genetic code and the signal transduction codes, a wide variety of new organic codes have come to light in recent years. Among them: the sequence codes (Trifonov 1987, 1989, 1999), the Hox code (Paul Hunt et al. 1991 Kessel and Gruss 1991), the adhesive code (Redies and Takeichi 1996 Shapiro and Colman 1999), the splicing codes (Barbieri 2003 Fu 2004 Matlin et al. 2005 Pertea et al. 2007 Wang and Burge 2008 Barash et al. 2010 Dhir et al. 2010), the signal transduction codes (Barbieri 2003), the histone code (Strahl and Allis 2000 Jenuwein and Allis 2001 Turner 2000, 2002, 2007 Kühn and Hofmeyr 2014), the sugar code (Gabius 2000, 2009), the compartment codes (Barbieri 2003), the cytoskeleton codes (Barbieri 2003 Gimona 2008), the transcriptional code (Jessell 2000 Marquard and Pfaff 2001 Ruiz i Altaba et al. 2003 Flames et al. 2007), the neural code (Nicolelis and Ribeiro 2006 Nicolelis 2011), a neural code for taste (Di Lorenzo 2000 Hallock and Di Lorenzo 2006), an odorant receptor code (Dudai 1999 Ray et al. 2006), a space code in the hippocampus (O’Keefe and Burgess 1996, 2005 Hafting et al. 2005 Brandon and Hasselmo 2009 Papoutsi et al. 2009), the apoptosis code (Basañez and Hardwick 2008 Füllgrabe et al. 2010), the tubulin code (Verhey and Gaertig 2007), the nuclear signalling code (Maraldi 2008), the injective organic codes (De Beule et al. 2011), the molecular codes (Görlich et al. 2011 Görlich and Dittrich 2013), the ubiquitin code (Komander and Rape 2012), the bioelectric code (Tseng and Levin 2013 Levin 2014), the acoustic codes (Farina and Pieretti 2014), the glycomic code (Buckeridge and De Souza 2014 Tavares and Buckeridge 2015) and the Redox code (Jones and Sies 2015).

The living world, in short, is literally teeming with organic codes, and yet so far their discoveries have only circulated in small circles and have not attracted the attention of the scientific community at large.

Code Biology

Code Biology is the study of all codes of life with the standard methods of science. The genetic code and the codes of culture have been known for a long time and represent the historical foundation of Code Biology. What is really new in this field is the study of all codes that came after the genetic code and before the codes of culture. The existence of these codes is an experimental fact – let us never forget this – but also more than that. It is one of those facts that have extraordinary theoretical implications.

The first is the role that the organic codes had in the history of life. The genetic code was a precondition for the origin of the first cells, the signal transduction codes divided the descendants of the common ancestor into the primary kingdoms of Archaea, Bacteria and Eukarya, the splicing codes were instrumental to the origin of the nucleus, the histone code provided the rules of chromatin, and the cytoskeleton codes allowed the Eukarya to perform internal movements, including those of mitosis and meiosis (Barbieri 2003, 2015). The greatest events of macroevolution, in other words, were associated with the appearance of new organic codes, and this gives us a completely new understanding of the history of life.

The second great implication is the fact that the organic codes have been highly conserved in evolution, which means that they are the great invariants of life, the sole entities that have been perpetuated while everything else has been changed. Code Biology, in short, is uncovering a new history of life and bringing to light new fundamental concepts. It truly is a new science, the exploration of a vast and still largely unexplored dimension of the living world, the real new frontier of biology.


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The question of the origin of life on Earth can largely be reduced to the question of what was the first molecular replicator system that was able to replicate and evolve under the presumably very harsh conditions on the early Earth. It is unlikely that a functional RNA could have existed under such conditions and it is generally assumed that some other kind of information system preceded the RNA world. Here, I present an informational molecular system that is stable, self-replicative, environmentally responsive, and evolvable under conditions characterized by high temperatures, ultraviolet and cosmic radiation. This postulated pregenetic system is based on the amyloid fold, a functionally unique polypeptide fold characterized by a cross beta-sheet structure in which the beta strands are arranged perpendicular to the fiber axis. Beside an extraordinary structural robustness, the amyloid fold possesses a unique ability to transmit information by a three-dimensional templating mechanism. In amyloidogenesis short peptide monomers are added one by one to the growing end of the fiber. From the same monomeric subunits several structural variants of amyloid may be formed. Then, in a self-replicative mode, a specific amyloid conformer can act as a template and confer its spatially encoded information to daughter molecular entities in a repetitive way. In this process, the specific conformational information, the spatially changed organization, is transmitted the coding element is the steric zipper structure, and recognition occurs by amino acid side chain complementarity. The amyloid information system fulfills several basic requirements of a primordial evolvable replicator system: (i) it is stable under the presumed primitive Earth conditions, (ii) the monomeric building blocks of the informational polymer can be formed from available prebiotic compounds, (iii) the system is self-assembling and self-replicative and (iv) it is adaptive to changes in the environment and evolvable.

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______________ Chapter 8 Photosynthesis Section 8-1 Energy and Life (pages 201-203) This section explains where plants get the energy they need Have a look at the concept map below for 'Photosynthesis and Respiration'. All organisms release energy from food, called. " What type of energy does food contain? Chloroplasts are a type of organelle found only in plant cells. This energy is contained in the chemical bonds of ATP molecules. This question was specifically included to introduce learners to the concept of validity and teachers are encouraged to allow learners to debate this issue in the class. Present your report on separate paper. Photosynthesis is essential for all life on earth, What is the chemical energy in the cell called? Presentation on theme: " Chapter 8 Photosynthesis. 8-1 Energy and Life Autotrophs Make their own food 8-1 Energy and Life."- Presentation transcript: Ensure that learners understand that respiration occurs constantly, during the day and night. Transcript of 8.1 Energy and Life. 8.2 Photosynthesis: An overview Chapter 8 Photosynthesis 8.3 The Light-Dependent Reactions: Generating ATP and NADPH chapter 8 photosynthesis section 8 1 energy and life answer key PDF photosynthesis making energy worksheet and answer key PDF photosynthesis making energy.. The relationships between different concepts are shown using arrows with linking phrases, such as "results in", "includes", "can be", "used to", "depends on", etc. Discussion: Assess learners ability to explain their results. And so on! All organisms release the stored potential energy from the food that they eat to support their life processes. However, in order to store large amounts of glucose, plants need to convert it into compounds which are insoluble in water. Discuss this with your learners.

This teacher's guide contains the full version of each concept map. The carbon dioxide that is produced in the body of an organism during respiration needs to be removed. Find out why plants that photosynthesise are green. Leave the leaf in the alcohol until all the chlorophyll has been removed from the leaf and the alcohol turns green. All living organisms can use energy in the form of chemical potential energy for the life photosynthesis. The energy from this Natural Sciences, chapter 8 photosynthesis section 8 1 energy and life answer key PDF photosynthesis section energy and life answers PDF 81 energy and life worksheet answer key.. Please emphasise to learners that they should refer to iodine solution, and not just iodine (which is a bluish black solid). Safety warning: remove the needles from the syringes, if there are any, before you hand out the syringes in class. chapter 8 photosynthesis section 8 1 energy and life answer key PDF section 3 reinforcement energy for life answers PDF 81 energy and life worksheet answer.. It starts off with carbon dioxide through limewater test and then demonstrates the starch test. Place the leaf into warm water to soften it. If you do not have time to do both parts of the investigation, a suggestion is to get your learners to read through Part 1, and then to conduct Part 2 where they have to write up their own report. We have now seen how plants produce food during photosynthesis. Comeback. The amount of iodine solution required to observe a result depends on the leaf tested. Describe what you observed when you blew air from your lungs through the limewater. After you have done part 1, you can do part 2 in the following lesson. For example, read the concept map as follows, "Respiration takes place in all organisms. We can represent respiration as an equation in the same way as we did for photosynthesis. They set up the following two experiments. Use a model to illustrate how photosynthesis transforms light energy Advanced High School Life Science Standards. Indicator 1: (Ch 8 Photosynthesis)

Photosynthesis 8 1 energy and life worksheet

Learners have already looked at photosynthesis and respiration in previous grades. 1/8 Photosynthesis Section Energy And Life Answers Scholastic Worksheet Answers Modern Chemistry Packet Answers Pre Algebra Semester 2 Practice Exam.. Often a concept map has a "focus question" from which the other concepts radiate. Teachers may also feel safer if they demonstrate this experiment. Should you wish to do so, you can make this distinction to your learners and introduce the term cellular respiration, however, it will only be clear once they have done cells in Gr. Think of an unripe green banana and a ripe yellow banana. Learners should be able to describe the taste and texture of each banana: the ripe one being soft and sweet, and the unripe one being firm and not too sweet. Figuring out the study method that works best for you, and developing these skills is very useful, especially for later in high school and after school! Encourage your learners to study the concept maps and make sense of them at the end of each chapter before doing the revision questions. Notice what happens to the clear limewater. Help them by reminding them of the two types of energy, namely kinetic energy and potential energy. Possible answers include: 'To determine whether leaves photosynthesise in the dark or the light', or 'To investigate whether Light is necessary for Photosynthesis'. This is because the energy is actually contained within the molecules produced (ATP). The process releases oxygen. Photosynthesis Section 8-1 Energy and Life Photosynthesis uses the energy of sunlight to convert water and Chapter 8, Photosynthesis Which method of testing is better to use and why do you say so? So how does this happen? Why do you think you observed the result you did when you pushed air from the atmosphere through the limewater? 8-1 Energy and Life & 8-2 Photosynthesis6 terms by gcosgrove3 organisms that obtain energy from other organisms ATP consists of adenine Next term in Matter and Materials, we will look at chemical reactions and define the 'ingredients' as reactants. The steps in the method must be numbered. Real understanding and knowledge comes from grappling with the subject matter, and not just memorizing facts. Therefore, to see if a plant photosynthesises, we can test to see if the plant produced starch. There is a very well known test for detecting carbon dioxide using clear limewater. You can also take a walk around your school property and surrounds to see if you can find any variegated leaves. This is useful to the plant as it means it can transport the glucose in water to where it is needed elsewhere in the plant. Companies! Blow bubbles through the rubber tube into the beaker marked BREATH, as shown in the diagram. The conclusion is that unripe bananas contain more starch than ripe bananas. Iodine solution is dripped on it. You should place one set of pot plants in the cupboard the day before you want to do part 1 of the investigation. For now, let's use this test to show that our breath contains carbon dioxide. Biology Fall Final - Chapter 8: Photosynthesis 2012 - 8.1 Energy and Life - 8.2 Photosynthesis: of photosynthesis in which energy from ATP and NADPH

A very small percentage of atmospheric air is carbon dioxide gas (0.03). This process is called respiration. So how do we test that our breath contains carbon dioxide? It is also important to make sure that the only thing affecting the limewater was the gas released in the experiment, and not carbon dioxide from the atmosphere. LIFE SCIENCE STANDARDS. LIFE SCIENCE STANDARDS. HS-LS1-5 Use a model to illustrate how photosynthesis What did you learn from doing this investigation? Draw air into the syringe from the atmosphere. In physiology, respiration refers to the transport of oxygen from the outside air to the cells and the transport of carbon dioxide out of the tissues and into the air. During photosynthesis in plants, oxygen is produced as a by-product. Cellulose is used to support and strengthen plants. You need to design this investigation yourself. This is the metabolic process in all organisms where oxygen is combined with glucose to release water and carbon dioxide and energy in the form of ATP (adenosine triphosphate).

Plants use radiant energy from the Sun in a series of chemical reactions to change carbon dioxide from the air and water from the soil into glucose. They are glucose (food) and oxygen. This is included as an introduction to the subsequent investigation. After this, place the leaf into the beaker with the ethyl alcohol. Some objects with potential energy are a book on the table (it has gravitational potential energy as it can fall down to the ground), a bouncing ball when it is at the top of its bounce as it can also fall back down, a batteries, fossil fuels have and food have potential energy. Remove one healthy looking leaf from the pot plants that were in the well-lit area exposed to direct sunlight. Limited Time Offer, Buy It Now! Learners need to learn how to learn! The "Key concepts" listed above is a summary written out in full sentences. Remember, food is the fuel for our bodies. INSIDE: • 8.1 Energy and Life. • 8.2 Photosynthesis: An Overview. 8.2 photosynthesis: an overview worksheet. Complete Worksheet if sub in class: They can also do this in groups. For example in this case you could read: "Respiration takes place in all organisms, releases energy from food".

Do you remember that we spoke about energy for movement (kinetic energy) and energy that is stored (potential energy) in Energy and Change in Gr. It is important that learners be made aware that we do not taste-test unknown substances due to the potential for poisoning. Our bodies need energy to move and do work. This investigation can be done over 2 lessons. Let's find out why. chapter 8 photosynthesis section 8 1 energy and life answer key PDF photosynthesis making energy worksheet answers PDF biology chapter8 energy and life.. When the ATP molecules are broken down they release the energy in order for other processes to take place. Have a look at the following photos of different plants. How to! The learners wanted to collect any gas that formed from the solution in Test Tube A and bubble it through the limewater. What three things are used to make glucose in photosynthesis? Light energy, Photosynthesis is Now that we know that plants produce glucose and change this into starch, we can find out if all leaves produce the same amount of starch through photosynthesis. Results: Learners should draw a table to record their results. A Gr. 4 learner wanted to grow some beans and carefully planted them in a yoghurt tub and watered them. ATP is not energy itself, but instead it stores energy. Let's find out.
2/25/2012 ·ň.1 Energy and Life from 8.1 Energy and Life By: Rojan Lotfdoust 1. 8.1 Energy light to energy into chemicalenergy. Photosynthesis 8.1 Energy and Life. Objectives. Explain the interrelationships between the processes of photosynthesis and cellular respiration comparing and contrasting Fill in the requirements of photosynthesis in the block on the left and fill in what type of energy is needed and the name of the pigment that absorbs the energy. What do you notice about the leaves? This being the first investigation that they will perform in high school, this activity will allow teachers to gauge their level of proficiency and abilities in this regard. You table should highlight the differences in requirements, the differences in the products, which organisms the processes takes place in, and when. Depending on what he planted the beans in, he might have noticed a root and first leaves forming. After conducting the investigation, you need to write up an experimental report of your findings. 8-1 Energy and Life Plants and some other types of organism are able to use light energy from the sun Chapter 8 Photosynthesis Vocabulary Review Class Variegated leaves have white patterns (areas lacking chlorophyll) on them. The starch test might show that the unripe banana contains more starch.

Watch the video: How Life Began w. Neil deGrasse Tyson NOVA Origins (May 2022).


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