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42 Cards in this Set
- Front
- Back
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Describe four processes needed for the spontaneous origin of life on Earth
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- Chemical reactions to produce simple organic molecules, such as amino acids, nucleotides and monosaccharides from inorganic molecules such as water, carbon dioxide and ammonia.
- Assmbly of these simple organic molecules into polymers, for example polypeptides from amino acids or nucleic acids from nucleotides. - Formation of polymers that can self-replicate - this allows inheritance of characteristics - The packaging of these molecules into membranes with an internal chemistry different from their surroundings. The result of these four processes would have been cell-like structures called protobionts. Natural selection could have operated on them, allowing evolution to begin. |
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Outline the experiments of Miller and Urey into the origin of organic compounds
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They investigated the theory that organic compounds could have formed spontaneously on Earth. They recreated the conditions that probably existed on Earth before living organisms were present. Inside their apparatus, they mixed the gases ammonia, methane and hydrogen to form a reducing atmosphere. Electrical discharges and the boiling and condensing of water stimulated lightning and rainfall. After one week, the clear water in the apparatus had turned to a murky brown. Analysis revealed many organic compounds, including 15 amino acids. Miller and Urey concluded that organic compounds could have spontaneously formed on Earth.
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State that comets may have delivered organic compounds to Earth
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Comets may have delivered organic compounds to Earth. Comets contain a variety of organic compounds. Heavy bombardment about 4,000 million years ago may have delivered both organic compounds and water to the early Earth.
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Discuss possible locations where conditions would have allowed the synthesis of organic compounds
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- Deep- sea hydrothermal vents - chemicals well up from around the rocks below, and spontaneously produce reduced comounds such as iron sulfide which can be oxidized to synthesise organic molecules. Heat as an energy source would allow for the assembly of polymers from monomers.
- Extraterrestrial sources - experiments by NASA have shown that organic compounds and proto-cells could have been formed in cold interstellar space, they might have then been delivered to Earth by meteorites, comets or interplanetary dust. - Volcanoes - volcanic eruptions involve the release of methane, ammonia, and hydrogen gases as well as water vapor, combined with lightning this creates the conditions of the Miller-Urey experiment. |
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Outline two properties of RNA that would have allowed it to play a role in the origin of life. Include the self-replicating and catalytic activities of RNA
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- Self-replicating - one molecule can form a template for the production of another molecule, following the rules of complementary base pairing, if the newly synthesized molecule is then used as a template, a replicate of the original molecule will be produced.
- Catalytic - RNA catalyses a broad range of chemical reactions. It could therefore have taken the role that is carried out by enzymes in the organisms that now exist on Earth. RNA still catalyses some reactions, such as the peptide bond formation during protein synthesis. |
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State that living cells may have been preceded by protobionts, with an internal chemical environment different from their surroundings
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Living cells may have been preceded by protobionts, with an internal chemical environment different from their surroundings. Examples include coacervates and microspheres.
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Outline the contribution of prokaryotes to the creation of an oxygen-rich atmosphere
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- Prokaryotes were the first organisms to use photosynthesis for the synthesis of organic compounds.
- When these organisms started to use water as a source of hyrdogen in photosynthesis, oxygen started being released as a waste product into the atmosphere. - There is evidence from the Greenland Rock dating that before this time there was little oxygen in the atmosphere. - Concentrations of oxygen built up quite quickly, and then other prokaryotic organisms were able to use aerobic cell respiration. |
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Discuss the endosymbiotic theory for the origin of eukaryotes
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- Eukaryotic cells contain mitochondria and chloroplasts, which are not found in prokaryotic cells. If eukaryotic cells evolved from prokaryotic cells, then the origin of these organelles must be explained.
- The endosymbiotic theory suggests that both mitochondria and chloroplasts have evolved from independant prokaryotic cells, which were taken into a larger heterotrophic cell by endocytosis. Instead of being digested, the cells were kept alive and continued to carry out aerobic respiration and photosynthesis. - Characteristics of mitochondria and chloroplasts provide some evidence: they grow and divide like cells, they have a naked loop of DNA like prokaryotes, they synthesize some of their own proteins using 70s ribosomes like prokaryotes, they have a double membrane (as expected when cells are taken into a vescicle by endocytosis. - Some biologists have suggested that flagella and cilia also have an endosymbiotic origin, but the evidence for this is less clear. |
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Define allele frequency and gene pool
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Allele frequency: the frequency of an allele, as a proportion of all alleles of the gene in the population.
Gene pool: all the genes in an interbreeding population. - The gene pool can be affected by: - Mutations - Natural selection - Immigration - Emigration - Population size - Mate selection |
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State that evolution involves a change in allele frequency in a population’s gene pool over a number of generations
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Evolution involves a change in allele frequency in a population’s gene pool over a number of generations. If natural selection is occurring the allelic frequencies will change.
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Discuss the definition of the term species
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- Before the discovery that species can evolve, a species was regarded as a type of living organism with fixed characteristics.
- Now, the biological definition of a species is a group of organisms with a common gene pool that can interbreed to produce fertile offspring. - This definition is widely accepted, however, it does cause some problems: - Many siblings have been found. These are species that cannot interbreed, but show no significant differences in appearance e.g the Pipistrelle bat in Britain. - Some pairs of species that are clearly different in their characteristics will interbreed e.g ruddy ducks and white-headed ducks. - Some species always reproduce asexually, meaning that members of a population do not interbreed. - Fossils cannot be classified according to the biological species definition, as it is impossible to decide with which organisms they would have been able to interbreed. |
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Describe three examples of barriers between gene pools
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- Temporal Isolation: If populations only breed at certain times of the year and are never in season at the same time, they cannot breed together.
- Hybrid Infertility: A hybrid is the fusion of gametes from different species, and is often sterile because they cannot produce gametes. - Geographical isolation: this acts as a physical barrier between the gene pools of populations. The populations can therefore split to form seperate species. |
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Explain how polyploidy can contribute to speciation
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• Polyploidy is ta condition in organisms whose cells contain more than two homologous sets of chromosomes. It occurs due to the failure of chromosomes to separate during meiosis to produce diploid gametes. Two diploid gametes then fuse to produce a tetraploid zygote, hence a new species.
• Polyplody is a form of sympatric speciation, meaning it occurs even when there is no separation of gene pools. It does not add any new genes to the gene pool, but creates new combinations of genes. |
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Compare allopatric and sympatric speciation
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- Allopatric speciation: occurs when members of a species migrate to a new area, forming a population that is geographically isolated from the rest of the species. The two isolated populations may be faced with different selective pressures. Therefore, changes in alleles and genotype frequencies occur.
- Sympatric speciation: occurs when two varieties of a species live in the same geographical area, but do not interbreed. This is generally because the environment has a variety of microhabitats in which the organisms live. Some organisms prefer to live in one particular habitat and fail to come in contact with others. They become genetically isolated for some time until they become reproductively isolated. |
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Outline the process of adaptive radiation
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Adaptive radiation occurs when species in a group diverge rapidly to fill a variety of ecological niches. This can happen when the group has a characteristic that gives it a competitive advantage over other existing species, or where there are opportunities that no other species is utilizing.
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Compare convergent and divergent evolution
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- Convergent evolution: Living organisms often find the same solutions to particular physiological problems. If natural selection acts in the same way, in different parts of the world, species can become remarkably similar, despite not being closely related. This is called convergent evolution. An example is the ocotillo cactus from the USA and the Allaudia euohorbia from Madagascar.
- Divergent evolution: Divergent evolution occurs when a single ancestral species evolves in very different ways. This allows them to adapt to different ecological niches, and avoid competition with each other. For example, the pentadactyl limb is derived from one ancestral mammal, but has gone to form a bat’s wing, a human hand, a horse’s hoof and many more structures. |
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Discuss ideas on the pace of evolution, including gradualism and punctuated equilibrium
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One idea surrounding the rate of evolution is called gradualism. It suggests that evolution proceeds very slowly, but large changes can take place gradually over long periods of time. However, the fossil records suggest something different. They show long periods of stability, with little evolution, followed by periods of sudden, major change. This is called punctuated equilibrium. The periods of stability could be due to equilibrium, where organisms become adapted to their environment, so natural selection acts to maintain their characteristics. The periods of sudden change may correspond with rapid environmental change, such as a volcano. New adaptations would then be required rapidly to cope with the environmental conditions.
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Describe one example of transient polymorphism
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If a population has two alleles of a gene, then the gene pool is polymorphic. If one allele is gradually replacing the other, the population shows transient polymorphism. An example of this is the peppered both. The moths can be light or dark; both forms are due to dominant alleles of a gene that effect wing colour. They started out mostly light coloured. However, during the industrial revolution coal-burning factories blackened nearby trees and the air. The light coloured moth could easily be seen by birds and other predators. However, the dark moths survived more easily and the dark colouring increased in the population
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Describe sickle-cell anemia as an example of balanced polymorphism
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Sometimes, two alleles of a gene can persist indefinitely in the gene pool of a population. This is called balanced polymorphism. An example of this is sickle cell anemia.
- Indiviuals with the genotype Hb Hb do not develop sickle cell anemia, but are susceptible to malaria. - Individuals with the genotype Hb Hb are resistant to malaria, but develop sickle cell anemia. - Heterozygous individuals do not develop sickle cell anemia, and are resistant to malaria. They are therefore the best adapted to areas where malaria is found. Both of the alleles of the hemoglobin gene therefore tend to persist in malarial areas. The sickle cell allele has increased in frequency to high levels in some of these areas, as they will be resistant to malaria. |
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Outline the method for dating rocks and fossils using radioisotopes, with reference to 14C and 40K
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• Accurate dating of fossils allows accurate sequencing of fossils
• Select 14C for young samples / samples from 1,000 to 100,000 years old • Select 40K for older samples / samples over 100,000 years old • Extract isotopes from sample • Measure isotopes in sample as proportion of 14C / 40K relative to breakdown products 14N / 40Ar • 14C/14N ratio decreases over time at a predictable rate / half-life = 5730 years • 40K/40Ar ratio decreases over time at a predictable rate / half-life = 1,250,000 years • Compare 14C/14N / 40K/40Ar ratio with decay curve to determine age of sample |
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Define half-life
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Half-life: the time required for half of the radioactive atoms in a sample to undergo decay. For example, the half-life of 14C is 5600 years
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Deduce the approximate age of materials based on a simple decay curve for a radioisotope
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Describe the major anatomical features that define humans as primates
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• Hands – grasping devices for climbing trees. Opposable thumb with grip for power and precision.
• Rotating forelimb – The hand can rotate through one hundred and eighty degrees. • Binocular vision – Eyes are closer together, able to see forwards to find food. • Visual acuity – increased numbers of rods/cones with own nerve cells. • Reduced olfaction (sense of smell) – reduced snout, flatter face. • Enlarged skull – expanded area of cerebrum, ventral foramen magnum • Large brain – increased sensory/motor areas, deeply fissured. • Few offspring – longer gestation. • Social dependency – corporate activities, group cohesion. • Strong musculature for moving up and around trees. • Long arms for climbing trees. |
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Outline the trends illustrated by the fossils of Ardipithecus ramidus, Australopithecus including A. afarensis and A. africanus, and Homo including H. habilis, H. erectus,
H. neanderthalensis and H. sapiens |
• all three genera are hominids
• increasing adaptation to bipedalism / forward movement of foramen magnum • increasing brain size in relation to body size • hominids originated in Africa and spread to other continents • Ardipithecus / Australopithecus / Homo fossils found in Africa • Homo erectus fossils found in Africa and in Asia • Homo neanderthalensis fossils found in Europe • Homo sapiens fossils found in all continents except Antarctica • decreasing relative size of face / jaw / teeth / canines • increasing relative size of brain case / forehead |
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State that, at various stages in hominid evolution, several species may have coexisted.
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At various stages in hominid evolution, several species may have coexisted.
An example of this is H. neanderthalensis and H. sapiens. |
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Discuss the incompleteness of the fossil record and the resulting uncertainties about human evolution
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• fossils being formed is a rare event
• This can be for many reasons, for example, few Neanderthals survived the cold, so few fossils. • fossils being preserved is a rare event • fossils being found is a rare event, for example due to geographical locations) • chances of finding fossils is improved by searching in the right geological strata • poor data / fragmented remains / very small sample size • more prone to paradigm shifts/changes in theory when data is limited / discovery of a small amount of fossils can lead to a huge change in theories • paleoanthropology can still be considered a science |
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Discuss the correlation between the change in diet and increase in brain size during hominid evolution
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• early hominids brain sizes were similar in size to those of apes
• early hominids had powerful jaws, indicates a mainly vegetarian diet • About 2.5 million years ago Africa became much cooler and drier and savanna grassland replaced forest • climate change may have prompted evolution of Homo and have prompted better / more sophisticated tools • climate change may have prompted change to hunting / killing large animals / increasing meat in diet • change in diet corresponds to the start of increase in hominid brain size • in apes and early hominids, brain growth slows after birth • Homo has rapid brain growth after birth • eating meat increases supply of protein / fat / energy making larger brain growth possible • hunting / killing prey on savannas is more difficult than gathering plant foods • natural selection possibly favoured larger brains / greater intelligence |
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Distinguish between genetic and cultural evolution
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• genetic evolution is a product of selection for (adaptive) genes
• genetic evolution produces heritable traits • genetic evolution is physically inherited as genes / coded within DNA • genetic evolution is affected by random mutation • natural selection determines likelihood of genetic inheritance • acquired characteristics are not inherited • genetic evolution occurs slowly / as gene pools alter gradually; • cultural evolution is inherited from the environment • cultural evolution is inherited independent of DNA • cultural evolution is (specific) learning / learning done during one's lifetime • cultural evolution can be directed • selection determines likelihood of inheritance; • cultural evolution can occur rapidly • genetic evolution is nature whereas cultural evolution is nurture |
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Discuss the relative importance of genetic and cultural evolution in the recent evolution of humans
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• cultural evolution based on skills / information passed from one generation to another
• new methods can be transmitted between different groups • cultural evolution is learned/taught/language dependent • large brains of Homo species allow more learning • cultural evolution allows more rapid evolution / most recent changes are cultural • genetic evolution is dependent on/controlled by genes • genetic evolution is limited by the genetic composition/genotypes of the populations • An example of human genetic evolution is an increase in cranial capacity • Examples of human cultural evolution include tool making/religion/art |
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Explain how the Hardy–Weinberg equation is derived
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• mathematical model for genetic equilibrium / from which predictions can be made
• used for sexually reproducing species / breeding must be random / population large / no migration / no selection / no mutation • used to calculate allele / genotype frequency • by sampling from a population • allele frequencies / genotype frequencies remain constant through generations / no change • if there is an observed change it suggests evolution is occurring (not just natural selection) / population is no longer in equilibrium • p and q represent the frequencies of two alleles of a gene • frequency of alleles adds to 1 / (p + q)2 • (genotype frequencies) p2 + 2pq + q2 = 1 • p2 and q2 are the frequencies of the homozygotes • 2pq is the frequency of the heterozygotes |
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Calculate allele, genotype and phenotype frequencies for two alleles of a gene, using the Hardy–Weinberg equation
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An example of this is a gene in which two alleles controls the ability to taste phenylthiocarbamide (PTC). The ability to taste PTC is due to the dominant allele (T) and non-tasting is due to the recessive allele (t).
- 1600 people were tested in a survey. 461 were non-tasters - a frequency of 0.288. - Their genotype was homozygous recessive (tt). - If q = frequency of t allele, q squared = .288 so q = .537 - If p = frequency of T allele, p = (1 - q) = .463 - The frequency of homozygous dominants (TT) and heterozygotes (Tt) can be calculated. - p squared = frequency of homozygous dominants - p squared = (.463)(.463) = .214 - 2pq = frequency of heterozygotes - 2pq = 2 (.463)(.537) = .497 |
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State the assumptions made when the Hardy–Weinberg equation is used
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It must be assumed that a population is large, with random mating and a constant allele frequency over time.
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Outline the value of classifying organisms
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• classification arranges organisms into groups
• classification allows identification of species / organisms • classification allows prediction of related taxa / based on common characteristics • classification reveals evolutionary links / shared derived characteristics / inherited from common ancestors • classification allows effective communication / all scientists use same terminology • classification avoids problem of convergence / ignores analogies • classification emphasizes homologous structures / traits derived from common ancestry |
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Explain the biochemical evidence provided by the universality of DNA and protein structures for the common ancestry of living organisms
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• DNA/genetic code is universal;
• same four bases adenine, cytosine, guanine and thymine • always pairing of A T and G C; • same structure of double helix of complementary strands; • use the same 20 amino acids in their proteins; • all left-handed; • same/similar enzymes in processes of replication/transcription/translation; • small differences in DNA/proteins show closer relationships; • e.g. hemoglobin/cytochrome C/gene structures show relationships among organisms; • humans have the same biochemistry as all organisms so part of same evolution/ common ancestry; • mitochondrial DNA used to determine maternal lines / y chromosome used to determine paternal lines; • endosymbiotic theory/mitochondria/chloroplast structures indicate common lines of evolution; |
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Discuss how biochemical variationscan be used as an evolutionary clock
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METHOD:
• differences in nucleotide base sequences / DNA / amino acid sequences / proteins accumulate gradually over time • differences accumulate at (roughly) predictable rates • therefore the number of differences can be used as a clock to measure the time since two divergent groups shared a common ancestor • For example. amino acid sequences in globin genes PROBLEMS: • however variations are partly due to mutations which are unpredictable chance events so there must be caution in interpreting data • establish a variety of molecular clocks for reliability |
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Explain how variations in specific molecules can indicate phylogeny
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• differences between molecules can be used to deduce phylogeny
• phylogeny is the evolutionary history of a (taxonomic) group • mutation rates in DNA occur with predictable rates • Comparisons can be made between nucleotide sequences of different taxa • Comparisons can be made between amino acid sequences (of proteins) of different taxa • differences can be used as a molecular clock to develop phylogeny, to determine time since common ancestry • variation can also be due to mutations; • mutations are chance events so caution must be taken when interpreting these |
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Define clade and cladistics
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Clade: a group of organisms that evolved from a common ancestor
Cladistics: a method of classification of living organisms based on the construction and analysis of cladograms |
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Distinguish, with examples, between analogous and homologous characteristics
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ANALOGOUS:
• analogous characteristics are structures with a common function but a different evolutionary origin • example: dolphin fins and shark fins HOMOLOGOUS: • homologous characteristics are structures that have a common evolutionary origin, even if they have different functions • example: dolphin forelimbs and human arms |
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Discuss the relationship between cladograms and the classification of living organisms
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• cladograms (often) confirm existing classifications since both are based on phylogeny
• cladograms are (sometimes) different than traditional classifications because nodes can be placed at any point / arbitrary • cladograms (sometimes) radically alter existing classifications • example: birds grouped with dinosaurs • strength of cladistics is that the comparisons are objective / rely on molecular homologies • weakness of cladistics is that molecular differences are based on probabilities |
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Analyse cladograms in terms of phylogenetic relationships
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Construct a simple cladogram
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Outline the methods used to construct cladograms and the conclusions that can be drawn from them
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Cladograms have been used to re-evaluate the classification of many groups of organisms.
Cladograms aim to work out how the difference in base or amino acid sequence could have evolved with the smallest number of mutations. It does not prove how evolution occured, but does give the most likely course. |
