evolution practice mark scheme

original concentration of the radioisotope must be established/estimated;
rate of decay/half-life of the isotope must be known;
in radiocarbon dating concentration of the surviving 14C in the fossil
is measured;
in potassium-argon dating ratio of 40K to 40Ar atoms are measured;
10000 years
increased bipedalism;
increased brain size/cranial capacity;
reduction of sagittal crest;
tooth size reduction;
flattening of the facial bones;
development of opposable thumb;
2 max
2 max
the non-living synthesis of simple organic molecules/amino acids from
inorganic molecules;
the assembly of these molecules into polymers/polypeptides;
the origin of self-replicating molecules that made inheritance possible;
the packaging of these molecules into membranes with an internal
chemistry different from their surroundings;
2 max
self-replicating and catalytic activities of RNA;
short sequences of RNA have been able to duplicate/copy other RNA
molecules accurately;
RNA enzyme/ribozyme (able to synthesize other molecules);
3-dimensional structure of ribosome catalytic sites (for peptide formation)
are composed of RNA;
able to store information in sequence of (4) nucleotides (similar to DNA);
2 max
two alleles in a gene pool/polymorphic;
one allele gradually replacing another;
due to strong selection pressure;
example; (e.g. melanic moths/industrial melanism)
3 max
periods of stability/little evolution/stasis, followed by periods of sudden
major change/lot of evolution/rapid speciation;
in periods of stability organisms become well-adapted to environment;
natural selection acts to maintain characteristics;
equilibrium punctuated by rapid environmental change;
such as volcanic eruption / meteor impact / change in sea level;
directional selection leads to rapid evolution;
4 max
IB Questionbank Biology
non-living synthesis of simple organic molecules;
from mixture of any three of methane, ammonia, water vapour
and hydrogen;
assembly of these organic molecules into polymers;
the origin of self-replicating molecules that made inheritance possible;
the packaging of these molecules into membranes with an internal
chemistry different from their surroundings;
binary fission of cell;
3 max
endosymbiosis theory states that eukaryotes are formed from prokaryotes;
symbiosis is an association between two or more species;
mitochondria of eukaryotes evolved from aerobic bacteria;
chloroplasts evolved from primitive autotrophic prokaryotes;
taken into larger heterotrophic cells by endocytosis;
eukaryotes formed membranes that could contain the prokaryotes;
mitochondria/chloroplasts have DNA/RNA similar to prokaryotes;
mitochondria/chloroplasts have double membrane;
3 max
forward facing eyes/binocular vision;
large brains;
flexible shoulder joints / shoulder blades on the dorsal side of the thorax;
manual dexterity / power grip / opposable thumb / grasping limbs;
finger pads / nails not claws;
skull adapted for upright posture;
pronation / rotating hand;
2 max
fossilization is an exceptionally rare occurrence;
most components of formerly living things tend to decompose relatively
quickly following death;
fossilization tends to favour hard body parts;
fossilization favours species that were widespread/lived for a long time;
paleoanthropology is an inductive/data-poor science (a relatively small
amount of data is used to draw conclusions);
many of the conclusions that have been drawn on limited data
have not stood for long;
exposed fossils are soon destroyed/weathered, reducing the chance
of them being found;
new discoveries regularly come to light, leading scientists to
re-interpret previous assumptions in the light of the new data;
examples e.g. the Dmansi site, Georgia, discoveries have led to a
re-evaluation of previous theories of human evolution;
3 max
all the genes in an (interbreeding) population
IB Questionbank Biology
both involve the formation of new species;
by the isolation of its genetic pool (in both cases);
both provide conditions for natural selection;
sympatric in same geographical area, allopatric in different;
sympatric could be reproductive/behavioural isolation while allopatric
physical isolation;
example of each; (e.g. allopatric speciation of Galapagos finches and
sympatric speciation due to polyploidy)
Award mark only where comparison is clear.
4 max
growth in brain requires more protein;
increased brain correlates with change of diet from plants/leaves to
fruit/meat (higher quality diet);
eating meat provides more protein;
larger brain implies more evolution as learning capacities increase;
2 max
the formation of new species by populations that inhabit the same or
overlapping geographic regions
a population colonizes a new habitat that involves unique selection
pressures / becomes geographically isolated;
eg Darwin’s finches;
eg some variants of wheat;
IB Questionbank Biology
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