IB DP Biology: Evolution, speciation and conservation of biodiversity (DP Biology) – Practice Questions

These are original questions written for Marlbridge, for revision and practice on this content. They are not reproduced past-paper questions, and they do not replicate the exam’s exact structure, question count or mark tariffs – the IB holds copyright in its own papers. Use these alongside the official past papers available through your school or the IB store.

These questions follow the IB Biology guide, first assessment 2025, sections A4.1 and A4.2. Questions marked (HL only) test additional higher level content (A4.1.8 to A4.1.11); the rest are SL and HL. Read the study guide first if you need explanations, and keep the revision notes beside you. Course pages: IB Biology hub, printable checklist and free 10-minute diagnostics.

Questions

1. Distinguish between evolution and a change that an organism acquires during its lifetime. [2]

2. Part of the same protein was sequenced in three species (hypothetical data).

Species	Amino acid sequence
X	ACDEFGHIKL
Y	ACDEFGHVKL
Z	ACNEYGHVRL

(a) Calculate the percentage difference between X and Z. [1] (b) Deduce which two species share the most recent common ancestor, and explain your answer. [2]

3. Outline how selective breeding of domesticated animals provides evidence for evolution. [3]

4. The arm of a human and the wing of a bird have the same bones in the same arrangement. The eye of an octopus and the eye of a human both form images but develop differently. (a) State the term for the structures in the arm and the wing. [1] (b) Explain how the eyes of the octopus and human illustrate convergent evolution. [3]

5. A region contains 2,400 species. Over a period, 85 new species form and 140 species become extinct. (a) Calculate the number of species at the end of the period. [1] (b) Explain why a population of finches that slowly becomes larger-beaked over time, remaining one species, is not an example of speciation. [2]

6. Bonobos live south of the Congo River and common chimpanzees live to the north. (a) Explain the role of geographical isolation in the divergence of the two species. [3] (b) Explain how differential selection contributes to the formation of separate species. [2]

7. (HL only) Two forms of a fish live in one lake. One form breeds in spring and the other in autumn. (a) State the type of reproductive isolation. [1] (b) Distinguish between sympatric and allopatric speciation. [2] (c) Outline why courtship behaviour usually prevents hybridization in animals. [2]

8. (HL only) Plant species P has 2n = 18 and species R has 2n = 22. They hybridize, and the hybrid is sterile. A fertile offspring later arises by polyploidy. (a) Calculate the chromosome number of the hybrid and of the fertile polyploid. [2] (b) Explain why the hybrid is sterile and why the polyploid is fertile. [3] (c) Explain why a mule is also sterile. [2]

9. (HL only) Explain how adaptive radiation increases the biodiversity of an island archipelago with vacant niches. [3]

10. A grassland survey recorded 62 species. A repeat survey by the same method recorded 51. (a) Calculate the percentage change in species richness. [2] (b) Explain why the abundance of each species should also be recorded. [2] (c) Evaluate the use of data collected by citizen scientists. [3]

11. Mixed dipterocarp forest in a Southeast Asian region covered 5,400 km² and, 12 years later, 4,320 km². (a) Calculate the mean area lost per year. [2] (b) Outline two human causes of the loss of this ecosystem. [2] (c) Outline the cause of extinction of the Caribbean monk seal. [2] (d) State the level of biodiversity that is reduced when a species goes extinct. [1]

12. A forest bird has few close relatives, and its forest is being cleared. Fewer than 200 remain. (a) Explain why EDGE of Existence would prioritize this species. [2] (b) Discuss the need for several approaches to conserving it, referring to in situ and ex situ methods. [6]

Answers

1. Evolution is a genetic change in the features of a population over generations [1]; an acquired change is not genetic, so is not passed on to offspring and is not evolution [1]. [2] Examiner insight: A “distinguish” answer needs both sides stated. Writing only what evolution is leaves the comparison unfinished.

2. (a) X and Z differ at positions 3, 5, 8 and 9, which is 4 of 10 [1]: 40%. [1] (b) X and Y differ by only 1 position (10%), fewer than the other pairs [1], so X and Y share the most recent common ancestor, because fewer differences mean less time since divergence [1]. [2] Examiner insight: State the counts for each pair as evidence. A conclusion without numbers is easy to lose marks on.

3. Breeds of one species, such as dogs, differ greatly in size, coat and behaviour [1]; the breeds and varieties arose from the original wild species in a short time [1]; this shows heritable variation exists and that selection of which individuals breed changes populations rapidly, as natural selection could [1]. [3] Examiner insight: Name a specific example and link it to heritable variation and selection. A statement that humans “changed” the animals is too vague.

4. (a) Homologous structures [1]. [1] (b) Both are structures used for the same function (forming images) [1]; but they have different evolutionary origins and develop differently, so are analogous [1]; similar selection pressures in unrelated lineages led to similar solutions, which is convergent evolution [1]. [3] Examiner insight: Mention both the shared function and the separate ancestry. Convergent evolution is the process; analogous is the term for the structures.

5. (a) 2,400 + 85 − 140 = 2,345 species [1]. [1] (b) Speciation is the splitting of a species into two [1]; gradual change in one lineage with no split leaves a single species [1]. [2] Examiner insight: Use the idea of splitting. Saying “the beak is just a change” does not explain the definition.

6. (a) The river separated an ancestral population [1], stopping gene flow between them (reproductive isolation) [1], so mutations and selection caused allele frequencies to diverge until they were separate species [1]. [3] (b) The environments on each side differed, so different alleles were favoured [1]; over generations the populations diverged in traits and could no longer interbreed successfully [1]. [2] Examiner insight: Link each step to the next. Naming the river without explaining the loss of gene flow gains little.

7. (a) Temporal isolation [1]. [1] (b) Sympatric speciation happens in the same area, with behavioural or temporal isolation [1]; allopatric speciation happens when populations are geographically separated [1]. [2] (c) Courtship behaviour is specific to a species [1]; an individual does not respond to the displays of another species, so mating between species is rare [1]. [2] Examiner insight: Part (b) needs a difference stated for each type. Part (c) should say why behaviour is species-specific, not just that it “prevents mating”.

8. (a) Hybrid: 9 + 11 = 20 [1]; polyploid: 2 × 20 = 40 [1]. [2] (b) Chromosomes from P and R are not homologous, so they cannot pair in meiosis [1]; viable gametes are not formed [1]; doubling gives each chromosome a partner, so meiosis works and gametes form [1]. [3] (c) A mule has 63 chromosomes, from a horse (32) and a donkey (31) [1]; they cannot all pair in meiosis, so it produces no viable gametes [1]. [2] Examiner insight: Quote the numbers in a calculation and then use them in the explanation. Unpaired chromosomes is the point; saying “hybrids are always sterile” is wrong, as polyploids show.

9. Adaptive radiation is the evolution of many related species from one ancestor [1]; each is adapted to a different vacant niche [1]; close relatives coexist without competing, so the number of species increases [1]. [3] Examiner insight: Include the vacant niches and the lack of competition. Without them the answer describes speciation only.

10. (a) (51 − 62) ÷ 62 × 100 [1] = −17.7% (a fall of 17.7%) [1]. [2] (b) Richness counts species only [1]; abundance shows evenness, so changes in dominance or declining populations are detected even if the species list is unchanged [1]. [2] (c) Strength: many observers cover more habitats and years at low cost [1]; limitation: variable identification skill or uneven sampling reduces reliability [1]; judgement: useful if methods are checked and validated against expert data [1]. [3] Examiner insight: An “evaluate” answer needs both sides and a conclusion. Calculate from the earlier value, and give the sign.

11. (a) 5,400 − 4,320 = 1,080 km² [1]; 1,080 ÷ 12 = 90 km² per year [1]. [2] (b) Any two, such as logging for timber [1] and clearance for plantations such as oil palm [1]; fire is also accepted. [2] (c) Hunted for oil and meat [1]; overfishing reduced the seals’ food supply [1]. [2] (d) Species diversity [1] (genetic diversity also falls). [1] Examiner insight: Give the cause of each loss by name. A statement that humans “destroyed” the forest is too general.

12. (a) It is evolutionarily distinct, with few close relatives, so its extinction would remove a large amount of unique evolutionary history [1]; it is globally endangered with a very small population [1]. [2] (b) Any six of the following: no single approach is sufficient [1]; in situ protection of the remaining forest in a managed reserve [1]; reclamation or rewilding of degraded forest to enlarge habitat [1]; ex situ captive breeding in a zoo as insurance against loss [1]; storage of germ plasm in tissue banks [1]; a reasoned judgement that a combination is needed, since different species require different measures [1]. Also acceptable: control of poaching or invasive species in the reserve. Further valid points earn no marks beyond six. [6] Examiner insight: A “discuss” answer should weigh approaches and reach a conclusion. A list of methods without a link to this bird will not reach the top of the mark range.

Where marks are usually lost

• Calling an acquired characteristic evolution.
• Giving conclusions about relatedness with no counts or percentages.
• Mixing up homologous and analogous.
• Counting gradual change in one lineage as speciation.
• Forgetting that geographical isolation works by stopping gene flow.
• Treating all hybrids as sterile and ignoring polyploidy.
• Dividing by the later value in percentage change.
• Describing causes of loss in general terms instead of naming the case study.
• Ignoring the ethical and economic debate in prioritizing species.

Next steps

• Review the revision notes and the study guide.
• Tick off outcomes on the printable checklist and return to the IB Biology hub.
• Take the free 10-minute diagnostics to find remaining gaps.
• Book a free trial class.

Official syllabus

International Baccalaureate Organization, Biology guide, first assessment 2025, published February 2023. Sections A4.1 and A4.2.