Practise IB Biology HL A4.1 with evidence-led questions on variation, selection pressure, adaptation, speciation and population change.
Species are groups of organisms that can potentially interbreed to produce fertile offspring.
Outline how new traits in a species can develop over time.
a. mutations generate variation/generate new traits;
b. mutations are changes to base/nucleotide sequence (of DNA/genes);
c. new alleles are formed by mutation;
d. meiosis/sexual reproduction generates new combinations of genes/alleles;
e. natural selection;
f. better adapted (individuals) have higher chance of survival;
g. better adapted (individuals) (tend to) produce more offspring/more likely to reach reproductive age;
h. heritability / traits/genes passed on (to offspring) / offspring inherit genes/alleles of their parents;
i. directional selection causes change in traits;
j. environmental change/environmental pressure causes selection of advantageous mutations/new traits;
k. antibiotic resistance/melanism in moths/other evidence-based example of development of new traits;
I. development of new traits over time is evolution;
Marking guidance:
Reject examples of speciation for mpk.
7
max
Explain how a new species can be formed abruptly by polyploidy.
a. polyploidy is having more than two sets of (homologous) chromosomes;
b. triploids have three sets of chromosomes/tetraploids have four sets of chromosomes;
c. polyploid/tetraploid cells generated from diploid cells by DNA replication without cytokinesis/non-disjunction (of all bivalents) during meiosis;
d. tetraploids produce diploid/2n gametes;
e. fusion of diploid and haploid gametes results in triploids;
f. triploids are sterile/no gametes produced because pairing of homologous chromosomes/meiosis fails;
g. diploids and tetraploids are reproductively isolated / tetraploids cannot interbreed with the diploid parent species / diploids and tetraploids only produce infertile offspring when they cross;
h. polyploids/tetraploids are therefore a different/new species (according to the biological species definition);
Marking guidance:
Reject polyspermy as the
origin of polyploid cells
5
max
Proteins play essential roles in all forms of life.
Describe how a protein that is common to many organisms can be used in evolutionary studies.
a. amino acid sequence of the protein from each organism is compared;
b. changes in (base/amino acid) sequence accumulate over time;
c. due to mutation;
d. positive correlation between number of (base/amino acid) differences between (two) species and time they diverged from a common ancestor
OR
fewer the (base/amino acid) differences, the less time since diverged from a common ancestor / more closely related;
e. cladograms illustrate probable sequence of divergence/evolutionary origins;
f. accumulation of mutations can be used as a molecular clock/allows time since evolutionary divergence to be estimated;
4 max
Cell biologists play an important role in research into disease, fertility, evolution and many other areas of science.
Outline the evidence for evolution provided by selective breeding.
a. crop plants/domesticated animals/livestock produced by selective breeding
b. specific example of a domesticated animal/crop plant and the wild species from which it was developed
OR
specific example of a domesticated animal/crop plant and the features in it which have been improved «compared with the wild species»
c. artificial selection/crossing selected varieties/eliminating undesirable varieties
d. «selective breeding/artificial selection can cause» significant/rapid change over time/from the original wild species
e. «changes due to selective breeding/artificial selection» shows natural selection can cause change/evolution «in a species»
For example dogs have been developed from wolves
3 max