1.
(a)
(b)
a group of related organisms sharing a common ancestor / a
group of organisms containing an ancestor and all of its
descendants / OWTTE
1
homologous structures evolved from a common ancestor while
analogous structures did not;
example of homologous and example of analogous; (both needed)
2
e.g. an example of homologous is pentadactyl limb in mammals
and birds / mouth parts in house fly and mosquito/other valid
example and an example of analogous is eye in vertebrates and
squid/octopus / wings of insect and bat / jointed legs of vertebrates
and insects/other valid example
(c)
Two correct labels for [1].
2 max
(d)
opposable thumbs (enable grabbing);
flat fingernails (instead of claws/for scratching);
forward-facing eyes for stereoscopic vision;
rotatable shoulder joints (for tree-climbing adaptation);
skull modified for upright posture;
large brain to body/skull ratio enables higher levels of thinking;
2 max
[7]
2.
(a)
(b)
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
all living organisms use DNA as genetic/hereditary material;
genetic code is (almost) universal;
idea that mutations accumulate gradually in DNA;
2 max
IB Questionbank Biology
1
(c)
(d)
A is most similar to B;
A is equally similar to C and D;
A is least similar to both C and D;
2 max
methods used to prepare cladograms use a different approach from
traditional classification/taxonomy;
show ancestral relationships;
reflect how recently two groups shared a common ancestry;
cladograms are (objective/accurate because they are usually) based
on molecular differences;
they should be considered as a good complement to traditional
classification;
2 max
[8]
3.
(a)
allele frequency: measurement of how often an allele appears (i.e. A or a);
gene pool: total sum of all the genetic information available for reproduction
within the population;
Both responses are needed to award the mark.
1 max
(b)
large population;
random mating;
no migration / immigration / emigration;
no mutations;
no natural selection;
(c)
1 max
phylogeny is the evolutionary line of descent;
(e.g. mitochondrialDNA /
the study of similar molecules in two different species; 
hemoglobin / Cytochrome c)
the greater the differences, the longer the time span since the two species
had a common ancestor;
variation can be due to mutations;
mutations are chance events so caution must be taken when interpreting
these;
3 max
(d)
organization of data helps to identify organisms;
suggests evolutionary links;
suggests the closeness of a relationship the more similar the
characteristics are;
allows prediction of characteristics shared by members of a group;
2 max
[7]
IB Questionbank Biology
2
4.
(a)
analogous: [2 max]
similar structures but different (evolutionary) origins / different basic
structure but same function;
e.g. vertebrate and invertebrate eyes / insect and human legs;
Accept any other valid example.
homologous: [2 max]
structures are of similar origin / same basic structure but different functions;
e.g. pentadactyl limbs in vertebrates;
Accept any other valid example.
(b)
4
 Accept examples
for two alleles of a given genetic characteristic, three 
of genotypes.
possible genotypes exist;
predicts frequencies of dominant and recessive alleles of a given gene;
homozygous for each allele and heterozygous;
frequency of dominant allele = p, recessive/albino allele = q;
total frequency of both alleles = 1 or p + q = 1;
random mating, probability of receiving two dominant alleles is p × p or p2;
probability of receiving two recessive alleles is q ×q or q2;
expected frequency of heterozygous genotype is 2pq;
p2 + 2pq + q2 = 1;
assumes no mutations / large population / random mating / no selective
pressure / no immigration nor emigration;
explains why recessive alleles do not disappear over several generations;
1
q2 =
or q = 0.007 (frequency of recessive);
20 000
p = 1 – 0.007 or 0.993;
frequency of dominant p2 = 0.986 or 98.6%;
frequency of heterozygotes 2pq = 0.014 or 1.4%;
Accept values with more significant figures.
5 max
[9]
IB Questionbank Biology
3
5.
DNA/genetic code is universal;
To award the mark full
same four bases adenine, cytosine, guanine and thymine; 
names of all four are required.
always pairing of AT and GC;
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;
6 max
[6]
6.
(a)
(b)
on Maui T. stelarobusta and T. eurychasma are closely related based
on the cladogram (but they produce different webs);
distantly related spiders, eg T. hawaiensis and T. stelarobusta
produce similar webs but are on different islands;
suggesting island is better indicator for relatedness than webs;
data inconclusive / more studies needed;
2 max
(mt) DNA is isolated from organism / species;
(mt) DNA is sequenced / order of bases determined;
(mt) DNA sequence is compared between organisms / species;
more similarities between sequences signify more closely related /
recent divergence;
fewer similarities between sequences signify less relatedness / more
distant divergence;
cladograms are calculated by software that depicts the cladogram with the
fewest number of branches;
for rooting the cladogram an outgroup / distantly related species is used;
3 max
IB Questionbank Biology
4
(c)
(i)
Award [2] max
Definition of convergent evolution: independent evolution of
similar traits in response to similar environments;
Evidence for: T. stelarobusta (Maui) and T. hawaiensis (Hawai’i)
produce the same type of web;
T. filiciphilia (Maui) and “eurylike” (O’ahu) also produce similar webs;
(ii)
Definition of adaptive evolution: rapid speciation to fill
ecological niches;
Evidence for: on Maui, all three T. species present produce
three different kinds of webs;
3 max
[8]
IB Questionbank Biology
5