Option D

Rachel M.MichalEnkhjin

Describe four processes needed for the spontaneous origin of life on

earth.• Process 1: synthesis of simple organic molecules• Process 2: assembly of simple organic molecules

into polymers• Process 3: formation of polymers that can self-

replicate• Process 4: the packaging of these molecules into

membranes with an internal chemistry different from their surroundings, including polymers that held the genetic information.

Outline the experiments of Miller and Urey

• simulate reducing atmosphere– Miller/Urey: water vapor, hydrogen, methane,

ammonia

• simulate high energy source– Miller/Urey: electric spark simulates lightning

• Products– Miller/Urey: mixture of amino acids

State that 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.

Discuss possible locations where conditions would have allowed the synthesis of organic compounds

Examples should include communities around deep-sea hydrothermal vents, volcanoes and extraterrestrial locations.

· Deep sea vents: ammonia and methane are present, and were not present elsewhere in the early atmosphere. There are many organisms currently living around deep sea vents suggesting this is a possible explanation.

· Volcanoes: volcanic eruptions involve the release of methane, ammonia, and hydrogen gases as well as water vapor. This, when combined with lightning, creates a real-life version of the Miller-Urey experiment.

· Extraterrestrial locations: Comets contain a variety of organic compounds. Heavy bombardment may have delivered both organic compounds and water to the early Earth.

Outline two properties of RNA that would have allowed it to play a role in the origin of life

• Scientists believe that RNA is most likely to have been the first genetic material on Earth. DNA replication requires enzymes and enzymes did not exist on prebiotic Earth. Under certain conditions RNA can replicate itself without the use of enzymes which makes it the more likely candidate for the first genetic material.

• Research has shown that RNA can carry out a number of enzyme-like catalytic

functions. They can also make complementary copies of short pieces of RNA as long as it has the nucleotides needed to build the RNA.

• They believe that small molecules of RNA which had the ability to carry genetic information also had the ability to replicate and store information about the cell-like spheres (protobionts) they were carried in.

• This RNA found in protobionts would have carried very limited genetic

information and the most successful protobionts would flourish and increase in numbers (natural selection).

State that living cells may have been preceded by protobionts, with an internal chemical environment

different from their surroundings

• When clay dries amino acids can spontaneously from polypeptides and in the right conditions a protenoid microsphere can be formed from these chains. These tiny bubble-like structures could surround other polymers and allow condition inside the microsphere to remain different from the external environment.

• There could also be another sphere known as a coacervte; a lipid

sphere that forms in water due to the hydrophobic properties of lipids. These microspheres could also keep a different internal chemical environment along with eh capacity to be selectively permeable.

• These structures are both known as protobionts and they are considered an important step in the formation of cells.

Outline the contribution of prokaryotes to the creation of an oxygen-rich atmosphere

• Bacteria, specifically anaerobic bacteria are believed to be the first forms of life on Earth. They consumed organic materials and reproduced to such numbers that competition was high and food was scarce.

• It is unclear how it happened but some bacteria evolved to become photosynthetic. When this happened they began releasing a waste product into the air called oxygen. Some of the oxygen killed off the high population of bacteria and the ones who survived were living deep in the mud or other areas protected from the oxygen in the atmosphere.

• The ability to make its own food led these prokaryotes to

reproduce and increase in significant numbers further increasing the oxygen in our atmosphere.

Discuss the endosymbiotic theory for the origin of eukaryotes

• Prokaryotes or bacteria were the first forms of life on Earth and the only form from 3.8 billion to about 2 billion years ago. Scientists know this because that is when fossils started showing cells that contain a nucleus, unlike the prokaryotic cells.

• The theory of endosymbiosis is a widely accepted theory that attempts to explain how prokaryotes evolved into eukaryotes; cells with a nucleus and membrane bound organelles. The theory states that large organelles inside eukaryotic cells such as the mitochondria and chloroplasts were once independent organisms that were taken in by a bigger cell and kept alive to perform important functions.

• It is believed that some cells lacked an enzyme needed to digest the prokaryote so instead the engulfed cell stayed alive inside the host cell and increased the cell’s ability to produce energy.

• By natural selection the cells with the ability to photosynthesize or metabolize nutrients efficiently would be most likely to survive and flourish.

• This theory explains how mitochondria and chloroplast became part of eukaryotic cells and it is supported by characteristics of these two organelles which make them different from the others. First of all they have their own DNA; a naked loop similar to that of prokaryotes. Secondly, they have their own double membrane. Thirdly, they are able to replicate themselves when more are needed and last they have the ability to perform protein synthesis using ribosomes.

• Although there are many questions answered by this theory several still remain. There is no guarantee that an engulfed cell would be copied and passed onto offspring. Also, when you remove a mitochondrion or chloroplast from a cell they cannot survive on their own.

Define allele frequency and gene pool

• Allele frequency: proportion or percent of a specific variation of a gene in a population.

• Gene pool: all of the genetic information present in the reproducing members of a population.

State evolution involves a change in allele frequency in a population’s gene pool over a

number of generations• Evolution results in changes to some alleles

after many generations of natural selection. Alleles that have proven to be advantageous become more frequent while those that as disadvantageous are not assed on to the next generation. Immigration and emigration can also have an impact on allele frequency within a population’s gene pool.

Discuss the definition of the term species

• The morphological definition of the term species states that it is a type of living organism with fixed characteristics that distinguish it from other species. This definition is very helpful in identifying organisms that have similar physiological and morphological characteristics, the ability to interbreed to produce fertile offspring, genetically distinct from other species, and have a common phylogeny. The biological definition of a species is a group of actually or potentially interbreeding populations with a common gene pool, which are reproductively isolated from other such groups. There are some complications or challenges to the biological definition of a species and they include the following. Some members of separate but similar species reproduce successfully and produce an offspring that is of neither species. The zonkey at the zoo in Aylesford is an example of a hybrid. The offspring however is infertile because the chromosome numbers are not the same in the parents. Another example is a liger as seen below. It is a hybrid of a male lion and female tiger. The hybrid is considerably larger than either parent.

Describe three examples of barriers between gene pools.

• Geographical isolation: physical barriers that prevent males and females from seeing each other. (e.g: mountains and rivers).

• Temporal isolation: incompatible time frames for mature gametes to come in contact with one another. (e.g: if female part of flower reaches maturity before the pollen is released or vice versa it will make reproduction difficult)

• Behavioral isolation: the habits and lifestyles of one population do not match that of another population. (e.g: many species of birds rely on courtship display to initiate sexual reproduction.)

Explain how polypliody can contribute to speciation

• Speciation is the process of a population that is evolving which changes so significantly that producing an offspring with a member of the original population is impossible.

• Polypliody refers to the situation in which a cell contains 2 or more sets of chromosomes. You have previously

Outline the process of adaptive radiation

Adaptive radiation is when a species divides, and then evolves in different ways depending on their environment to fill their ecological niche. This evolution occurs because some species are better suited to inhabit that environment, so they have a better chance of surviving longer and creating offspring.On the Galapagos islands, for example, finches have evolved into about 13 different species which all stem from the same ancestor species. These species are varied from the ancestor species in order to fill the niches of the different islands.

Compare convergent and divergent evolution

• Convergent evolution is when different species become more similar over time, sharing analogous traits due to the environment’s niche.

• Divergent evolution is when the same species evolves in such a way that differences appear in individuals in a species, and groups become less and less similar over time. This is usually due to a group of organisms separating to different environments.

Discuss ideas on the pace of evolution, including gradualism and punctuated equilibrium

• Gradualism is the slow change of a species from one form to another. This could happen if an environment is not especially extreme, so changes can happen more slowly and species don’t need to evolve rapidly in order to stay alive

• Punctuated equilibrium implies long periods without appreciable change, and then short periods of rapid evolution. This would take place if an environment changed rapidly, causing a need for a species to evolve if they want to have any hope of survival.

Describe one example of transient polymorphism

• Transient polymorphism is when the frequency of a phenotype changes in an area over time.

• Example – During industrialization in England, dark colored peppered moths gradually became more dominant in England than lighter-colored peppered moths, due to the environment. This is because trees became darker and darker as industrialization polluted the area, so darker moths blended in well and avoided being pecked by birds or preyed upon.

Describe sickle-cell anemia as an example of balanced polymorphism

• When an individual has homologous recessive trait for sickle cells, they will have sickle celled anemia, because their red blood cells will be sickle shaped. However, when an individual only has one allele for the trait (making them heterozygous), they become resistant to malaria. For this reason, the gene for sickle cell has not died out. So, the frequency of the gene remains balanced and constant-ish.

Outline the method for dating rocks and fossils using radioscopes with reference to 14C and 40K.

• Fossils contain elements called isotopes from the living matter that used to exist. If isotopes are unstable, they will decompose over time. Each radioactive isotope has a fixed half life, and using the relative abundance of reactants and decayed products in a substance, biologists can estimate the age of fossils. 14C (Carbon 14) has a half life of 5000 years, so it can be helpful in identifying the age of fossils younger than 100,000 years old. Potassium-40 (40 K) has a half life of 1.3 billion years, so it’s more useful in identifying much older fossils.

Define half-life

• An element’s half life is the amount of time it would take for half of a radioactive element to decay.

Deduce the approximate age of materials based on a simple decay curve for a radioisotope

• Count how many times the abundance of radioactive isotope has halved (when it’s ½ the original concentration, then ¼, then 1/8, then 1/16, etc…). Next, evaluate how long it took for the isotope to halve. Multiply the number of years in one half-life by the number of halves that have taken place.

Describe the major anatomical features that define humans as primates

• Vision: eyes are close together on the front of the face, allows for over-lapping fields of vision and good depth perception (3D). Color vision.

• Parental care: humans (and primates) have a longer gestation period that other mammals and single births are the norm. Long nurturing period for offspring.

• Dexterous hands with opposable thumbs. Nails on digits. Tactile pads at the end of digits.

• Collarbone: allows for a flexible shoulder joint, which allows for movement in 3 dimensions.

• Brain size: brain is larger and more developed/complex than most other mammals.

• Teeth are arranged so primates can have an omnivorous diet.

Outline 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

• Trend: migration out of Africa• Trend: increased adaption to bipedalism (pelvis, fully extendable knees, stronger

legs/weaker arms, platform-like foot without opposable toes)• Trend: decreasing relative size of face, jaw, teeth, especially canines; increasing

relative size of brain case, forehead. • A. afarensis: 3-3.9 million years, ape-like face.• A. africanus: 2.3-3 millions years. Flatter face, larger molars for plant based diet. • A. robustus: 1-2.2 million years. Very large bones, molars and skull.• H. habilis: 1.6-2.4 million years. Smaller teeth and jaw for a meatier diet. First to

use tools. Sized like humans. • H. erectus: .4-1.8 million years. More complex tools – thus meat is a bigger part of

diet. Teeth changed. • H. neanderthalensis: .5 million years. Larger brains and bones, large teeth and jaw,

shorter limbs for the cold. • H. sapiens: .1 million years. Large brain, flat face, reduced teeth, reduced

robustness, chin.

State that, at various stages in hominid evolution, sever species may have

coexisted.• Yes, several species may have existed at once

during hominid evolution. For example, habilis and erectus most likely existed at the same time, as well as erectus and neanderthalensis, and neanderthalensis and sapien.

Discuss the incompleteness of the fossil record and the resulting uncertainties about human evolution

• In order to tell the age of fossils it is helpful for all the bones in a body to have been distributed and preserved in one place. Because many hominids were preyed upon, fossils are spread out. An organism also needs to have hard parts and be buried in an anaerobic environment very quickly, which wasn’t always the case. There are a lot of missing links in between species and it is hard to say with certainty when certain species officially died out or began.

• It cannot be ensured that the hypothesis for hominid evolution is complete or accurate.

Discuss the correlation between the change in diet and increase in brain size during hominid

evolution• Larger brains require more energy to operate. A

change in diet from mostly veggies to including more meat would support and increase in brain size because meat is generally a little more caloric and fatty, and would support the usage of brain energy. Protein increase also enables brain growth.

• Also, hunting and killing prey on savannas is more difficult than gathering plant foods, so natural selection might have favored larger brains with greater intelligence.

Distinguish between genetic and cultural evolution

• Cultural evolution is a difference in the behaviors and mannerisms of a species, for example a change in traditions or tools used, types of shelters created, things eaten, etc.

• Genetic evolution is a change in the genetic make-up of a species.

• Genetic evolution (increase in brain capacity) hasn’t really changed much in homo sapiens. Cultural evolution, however, constantly changes. A lot of our evolution as a society draws on our experiences as a species, and that kind of past knowledge, not necessarily advanced intelligence.

Discuss the relative importance of genetic and cultural evolution in the recent evolution of humans

Evolution of the brain allowed cultural evolution to take off. Since then cultural evolution has been able to change humans far more quickly than genetic evolution has. Human behavior and life has changed greatly without much genetic evolution at all. We are now able to change our environment instead of changing to suit our environment

Explain how the Hardy-Weinberg equation is derivedp squared + 2pq +q squared = 1

• p represents the frequency of the dominant allele and q the frequency of the recessive allele

• When gametes combine their alleles to form zygotes, the probability of AA (A being the dominant allele) is p squared. The probability of aa is q squared. There are two ways in which an Aa genotype can arise, depending on which parent contributes the dominant allele.

Calculate allele, genotype and phenotype frequencies for two alleles of a gene, using the Hardy-Weinberg equation

• 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

State the assumption made when the Hardy-Weinberg equation is used

• A population is large, with random mating and constant allele frequency over time. This implies no allele-specific mortality, no mutation, no emigration and no immigration.

Outline the value of classifying organisms

• 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

Explain the biochemical evidence provided by the universality of DNA and protein structures for the common ancestry of living organisms

• DNA/genetic code is universal;• same four bases adenine, cytosine, guanine and thymine; To award the mark full

names of all four are required.• 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;

Explain how variations in specific molecules can indicate phylogeny

• 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• compare nucleotide sequences (of DNA) between taxa• compare amino acid sequences (of proteins) between taxa• differences can be used as a molecular clock• to develop phylogeny• to determine time since common ancestry• variation can be due to mutations;• mutations are chance events so caution must be taken when

interpreting these

Discuss how biochemical variations can be used as an evolutionary clock

• 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• example; e.g. amino acid sequences in globin genes

Define clode and cladistics

• 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

• Nodes: branch points indicating the evolution of shared derived characteristics

Distinguish, with examples, between analogous and homologous characterisitcs

Analogous Characteristics:•analogous characteristics are structures with a common function•but a different evolutionary origin•example: dolphin fins and shark fins

Homologous Characteristics•homologous characteristics are structures that have a common evolutionary origin•even if they have different functions•example: dolphin forelimbs and human arms

Outline the methods used to construct cladograms and the conclusions that can be drawn from them

• The first step involves the construction of a list of all organisms that will be included in the cladogram.

• The next step involves compiling a list of characteristics possessed by these organisms. This list would normally involve morphological characteristics but a cladogram can be constructed based on biochemical data also.

• Ø Now you would need to look at the one trait that is common to all organisms and this would be the primitive characteristic (i.e., eukaryotic, multicellular, vertebrae).

• Ø The next step is to construct a table showing all of the derived characteristics on the top row and the names of the organism in column one.

Discuss the relationship between cladograms and the classification of living organisms

• 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