IB Biology HL A4.1 Evolution and Speciation Questions
Practise IB Biology HL A4.1 with evidence-led questions on variation, selection pressure, adaptation, speciation and population change.
- Syllabus
- First assessment 2025
- Course
- Biology HL
- Level
- HL
Exam points
- Define evolution as heritable change in populations and explain how selective breeding changes inherited characteristics over generations.
- Use DNA, RNA, amino-acid or protein sequence similarities and differences to infer common ancestry, phylogeny or divergence.
- Distinguish homologous and analogous structures and compare divergent with convergent evolution using ancestry, function, environments and selection pressures.
- Explain how isolation, differential selection and prezygotic or postzygotic barriers produce speciation, distinguishing allopatric and sympatric pathways.
- Explain adaptive radiation as divergence from one ancestor into ecological niches.
- Explain how polyploidy and chromosome doubling can cause abrupt plant speciation, reproductive isolation and restored fertility.
Covered syllabus points
A4.1.1—Evolution as change in heritable characteristicsA4.1.2—Evidence from sequencesA4.1.3—Evidence from selective breedingA4.1.4—Evidence from homologous structuresA4.1.5—Convergent evolutionA4.1.6—Speciation by splitting of pre-existing speciesA4.1.7—Reproductive isolation and differential selectionA4.1.8 (HL)—Sympatric vs. allopatric speciationA4.1.9 (HL)—Adaptive radiationA4.1.10 (HL)—Barriers to hybridizationA4.1.11 (HL)—Abrupt speciation in plants
Question 1
[Maximum number: 12]
Species are groups of organisms that can potentially interbreed to produce fertile offspring.
Question (a)
(a)
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;
Reject examples of speciation for mpk.
Question (b)
(b)
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);
Reject polyspermy as the origin of polyploid cells
Question 2
[Maximum number: 4]
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; |
Question 3
[Maximum number: 3]
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
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