Option D- Evolution

Option D - Evolution, IB biology: answers to ***. statements

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D.1.1 Describe the four processes needed for the s

1. Life is based on organic molecules. Earth had only inorganic matter. Where did they come from?

2. Organisms are organized. Monomers need to form polymers (eg polypeptides) to build complex organisms such as proteins.

3. To be considered "alive" it must reproduce. DNA (or RNA) used for replication, BUT DNA is a complex molecule - unlikely that it was developed early.  

4. Water tends to depolymerize molecules. Organic compounds dissolve in water  -->difficult for molecules to become organized into polymers.  

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D.1.2 Outline the experiments of Miller and Urey i

Miller and Urey, 1953. In a glass sphere in a laboratory --> reproduced environment as thought to have existed on Earth during Hadean.

  • gases: eg. methane, hydrogen, ammonia
  • liquid water, heated to evaporation and cooled to condense --> water cycle.
  • warm temperature
  • exposed to UV radiation, as no protection from ozone layer
  • electric sparks generated --> lightning

After a week : amino acids, certain sugars and nucleic acids formed. Building blocks of life but NOT "alive".

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D.1.3 State that Comets may have delivered organic

Ice chunks through space can organic compounds.

Earth bombarded with comets 4 billion years ago.

Nasa (2001): organic molecules could have survived

Such an impact could help polymerize amino acids into polypeptides.

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D.1.4 Discuss the possible locations where conditi

In Space Clouds of dust: presence of glycine, simplest amino acid. Difficult to confirm but experiments have been able to synthesize amino acids in similar conditions. PANSPERMIA

In Alternating Wet/Dry Conditions seashore, river where alternating wet and dry conditions. drying of clay --> could create catalysing reactions --> organic molecules. Stromatolites, ancient form of life live in these conditions.

Near volcanoes spews out water vapor, gases, minerals that could be used to form organic matter. raw material + warmth = conditions favourable for amino acids and sugars.

In deep oceans Hydrothermal vents: hot water emmanates from beneath ocean floor. Picks up countless minerals along the way. Entire communities live around these vents.

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D.1.5 Outline two properties of RNA that would hav

In certain conditions RNA is able to self-replicate.

RNA catalyses a range of chemical reactions. Could have taken the role of proteins.

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D.1.6 State that living cells may have been preced

When clay dries and heated: 200 amino acids can join to polypeptide chains. In right conditions --> proteinoid microspheres, "bubbles". If surrounded by other polymers could establish a chemistry imside which was different from that of surroundings.

Coacervates can form from lipids in water. Hydrophobic forces between water and lipid. chemical balance that is different + capacity to be selectively permeable.

Significant step towards formation of cells --> called protobionts. first cell membranes?

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D.1.7 Outline the contribution of prokaryotes to t

No oxygen 4 billion years ago. Bacteria --> anaerobic

Some bacteria advantegous as they could make their own food.

3500 years ago some bacteria developed capacity to photosynthesize. Oxygen became waste product of photisynthesis. --> Anaerobics decreased.

Current level of oxygen is 21 %.

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D.1.8 Discuss the endosymbiotic theory for the ori

States that organelles in cells were independent prokaryotes. --> being engulfed by bigger cells. Kept alive in exchange for services. Could explain how Mitochondria and Chloroplasts became part of another cell.

Characteristics that supports the theory as they have:

  • double membrane
  • Naked DNA, circular like prokaryotes
  • Synthesizes their own proteins using 70S ribosomes, like prokaryotes
  • can make copies of themselves.

However, does not guarantee that host cell can pass on its genetic code including the newly acquired organelle. Also, mitochondria and chloroplasts cannot survive on their own.

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D.2.1 Define "allele frequency" and "gene pool"

The gene pool is all the genes in an interbreeding population

As some alleles are commoner than others: the allele frequency is the frequency of an allele, as a proportion of all alleles of the gene in the population. 

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D.2.2 State that evolution involves a change in al

After generations of natural selection, some alleles have proven to be advantegous and tend to be more frequent.

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D.2.3 Discuss the definition of the term species

A species is made up of organisms that:

  • have similar physiological and morphological characteristics which can be observed and measured
  • have the ability to interbreed to produce fertile offspring
  • are genetically distinct from other species
  • have a common phylogeny

hybrids between two species that are related but not the same species?

what about 2 populations that could possibly interbreed but do not because of other factors, eg distance?

populations that reproduce asexually?

infertile individuals? technique of in virtro fertilization?

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D.2.4 Describe three examples barriers between gen

Geographical isolation

physical barriers such as land or water hinders interbreeding. --> separation of populations --> no contact.

Temporal isolation

incompatible time frame that prevent populations from encountering each other. One population of a species being ready to mate when another population of the same species is not.

Behavioural isolation

one population's lifestyle and habits are not compatible with those of another population. Hence, little or no reproduction will take place between the members of the two populations because of behavioural differences.

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D.2.5 Explain how polyploidy can contribute to spe

Polyploidy = three or more sets of chromosomes.

When cell divison does not completely separate the copies of chromosomes and they end up in the same cell. More common in plants.

--> more vigorous plants.

--> extra set of chromosomes = greater errors in replication more common.

eventually two populations has become so dissimilar that they no longer are the same species.

When production of offspring with the original population become impossible = speciation.

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D.2.6 Compare allopatric and sympatric speciation

Allopatric speciation: new species through physical barrier, geographically isolated.

Eg. lizards at galapagos islands.

Sympatric speciation: new species formed while living in the same geographical area.

behavioural or temporal barrier between gene pools

or hybrid infertility

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D.2.7 Outline the process of adaptive radiation

Similar populations become genetically different from each other. When the group has a characteristics that gives it competitive advantage over existing species or where there are opportunities that no other species are utilizing. Eg. Darwin's finches - Galapagos.

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D.2.8 Compare convergent and divergent evolution

divergent evolution: increases the morphological differences between species, as each species adapts to different ecological niches

convergent evolution: decreases morphological differences between species, as each species adapts to similar ecological niches

If natural selection works in the same way in different parts of the world species can become remarkably similar, despite not being closely related. It is "converse" of adaptive radiation. Unrelated species showing striking similarities such as Cacti and Euphorbias.

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D.2.9 Discuss ideas on the pace of evolution, incl

Gradualism: Evolution proceeds very slowly, but large changes can gradually take place over long periods of time.

Does not fit with fossil record --> shows periods of stability then sudden major changes.

Periods of stability - organisms well adapted to environment, natural selection acts to maintain characteristics.

Sudden change - may correspond with rapid environmental change.

Punctuated equilibrium: the changes are relatively quick and followed by long periods of little or no change

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D.2.10 Describe one example of transient polymorph

A population in which there are two alleles of a gene in the gene pool is polymorphic. If one allele is gradually replacing the other the population shows transient polymorphism.

Eg. the peppered moth. Both dark and light dominant alleles, but when air pollution made it favourable to be dark these alleles increased in frequency.

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D.2.11 Describe sickle cell anaemia as an example

Sometimes two alleles can persist indefintaley in the gene pool of a population: Balanced polymorphism

genotype HbA HbA do not develop sickle cell anemia but is susceptible to Malaria

genotype HbS HbS is resitent to malaria but develop severe sickle cell anemia

Heterozygous HbA HbS do not develop sickle cell anemia and is resistant to malaria. Best adaption where malaria can be found

Both of these alleles of hemoglobin gene therefore tend to persist in malarial areas.

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D.3.1 Outline the method of dating rocks and fossi

14C for young samples, from 1,000 to 100,000 years old

40K for older samples, over 100,000 years old

  • some fossils contain radioisotopes
  • many igneous rocks contain radioisotopes
  • 14C/14N decreases over time at a predictable rate (half-life = 5730 years)
  • 40K/40Ar decreases over time at a predictable rate (half-life = 1,250,000 years)
  • compare 14C/14N and 40K/40Ar ratios with decay curve to determine age of sample
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D.3.2 Define Half-life

Half-life: the time during which the radioactivity falls to half its original level

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D.3.3 Deduce the approximate age of materials base

Uploaded Image (http://intranet.canacad.ac.jp:3445/BiologyIBHL2/admin/image.html?imageid=200151)

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D.3.4 Describe the major anatomical features that

  • grasping limbs, with long fingers and a separated opposable thumb;
  • mobile arms, with shoulder joints allowing movement in three planes and the bones of the shoulder girdle allowing weight to be transferred via the arms;
  • stereoscopic vision, with forward facing eyes on a flattened face, giving overlapping fields of view;
  • skull modified for upright posture;
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D.3.5 Outline the trends illustrated by the fossil

  • increasing adaptation to bipedalism, especially forward movement of foramen magnum
  • increasing brain size in relation to body size
  • hominids originated in Africa and spread to other continents
  • Ardipithecus fossils found in Ethiopia
  • Australopithecus and Homo habilis fossils found in Southern and Eastern Africa
  • Homo erectus fossils found in Eastern 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, esp. canines; increasing relative size of brain case, forehead

See text book/revision guide for this question!!!!

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D.3.5 continued

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D.3.6 State that, at various stages in hominid evo

Overlap in fossil ages.

  • A. aferensis and A. africanus appr. 3 million years ago
  • H. erectus, H. neanderthalensis and H. sapiens appr. 100 000 years ago
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D.3.7 Discuss the incompleteness of the fossil rec

  • because the hominid fossil record is incomplete, it is unclear how the various hominid species are related
  • the fossil record for hominids is incomplete because it is difficult for remains of animals living in arid or semi-arid habitats to fossilize
  • fossils only form when buried under sediment before decomposition occurs;
  • animal bodies are usually eaten by detritivores, decomposed by bacteria, or broken down chemically
    • for example, organic acids react with alkali in bones and teeth
    • therefore, few fossils found of savanna-dwelling hominids;
    • of remains fossilized, most remain buried in sediment/ remain unfound;
    • hominid fossils that have been found may or may not be representative of hominid history;
    • hominid fossils that have been found are usually partial, and the remainder of the organism must be inferred/ inferences may or may not be correct;
    • only hard parts of individuals fossilize, leaving many questions concerning the rest of the individual’s phenotype;
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D.3.8 Discuss the correlation between the change i

Early hominids (Australopithecus):  brain sizes were similar in size to those of apes, powerful jaws and teeth indicate mainly vegetarian diet

About 2.5 million years ago Africa became much cooler and drier. Savannah grassland replaced forest. --> may have prompted evolution of Homo --> increasingly sophisticated tools --> change to hunting and 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 but Homo has rapid brain growth after birth


  • eating meat increases supply of protein, fat and energy, making larger brain growth possible
  • hunting and killing prey on savannas is more difficult than gathering plant foods, so natural selection might have favored larger brains with greater intelligence
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D.3.9 Distinguish between genetic and cultural evo

Cultural evolution: new methods, inventions or customs can be incorporated into what is passed on.

CE does not involve changes in allele frequencies in the gene pool. Changes due to CE can happen during one human lifetime, whereas genetic evolution happens over generations.

CE involves characteristics acquired during a person's life whereas GE involves characteristics that are inherited.

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D.3.10 Discuss the relative importance of genetic

  • cultural evolution has played an increasingly greater role in the lives of humans over time;
  • especially over the past few thousand years, during which human characteristics have changed hugely
  • genetic change happens too slowly to produce the huge changes in human culture;
  • some cultural changes have, such as medical advances, have reduced natural selection pressures between phenotypes
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