IB ESS HL 3.1 Biodiversity and Evolution Question Bank
Practise IB ESS HL 3.1 by analysing diversity indices and evidence for natural selection, isolation and speciation.
- Syllabus
- First assessment 2026
- Course
- ESS HL
- Level
- HL
Practise IB ESS HL 3.1 by analysing diversity indices and evidence for natural selection, isolation and speciation.

Figure:Global biodiversity extinction-risk categories

Figure:Changes in species extinction risk from 1980 to 2015
the two biodiversity charts shown above are based on records for species diversity. Identify one other factor that may be measured to assess the diversity of life on Earth.
a. genetic diversity;
b. habitat diversity;
Marking guidance:
Do not accept "evenness/equitability" or "richness" they are already included within concept of species diversity
Outline the mechanisms by which a terrestrial species may have evolved from an aquatic ancestor.
there was genetic variety in aquatic species/mutations accumulated over years;
b. certain features may have adaptation/advantage for terrestrial existence;
c. individuals with these features could colonize terrestrial habitat;
d. they would be more likely to survive/survival of the fittest/experience less competition (natural selection);
e. they produce offspring like themselves/feature will become more abundant;
f. individuals with feature may be unable to breed with others without feature /speciation occurs / reproductive/geographical barrier will give rise to new terrestrial species;
Explain the ways in which species diversity and an abundance of plant and herbivore species will increase the resilience of an ecosystem.
Diversity:
a. a greater diversity of plant and herbivore species would mean there are more species to take over the role of any that would be lost/creates a more complex food web;
b. a wider variety/diversity set of plant species will support a wider range of herbivores/increase habitat diversity;
c. a wider variety/diversity of plant species will be able to exploit a wider range of abiotic conditions;
d. more plant species/greater plant diversity will be more likely to include species that will survive a change in conditions;
e. a wider variety/diversity plant species will increase interspecific competition resulting in evolution of more species;
f. a wider variety/diversity of herbivorous species will support a wider range of predators;
g. a wider variety/diversity of herbivore species will occupy a wider range of niches adding to the complexity of the system;
Abundance:
h. a greater abundance/larger populations of plant species means greater primary productivity which supports a greater abundance/larger populations of herbivores;
i. a greater abundance/larger populations of plant species is less likely to become extinct from the ecosystem;
j. a greater abundance/larger populations of herbivores will support a greater abundance/larger populations of predators;
k. a greater abundance/larger populations of herbivores will be less likely to become extinct in the ecosystem;
Explain one natural and one human-caused factor that influences changes in biodiversity.
Natural factor [4 max]:
(Extinction)
a. mass extinctions of the past/local extinctions caused by various natural factors, have (temporarily) reduced biodiversity;
b. e.g. tectonic plate activity / super-volcanic eruption;
c. e.g. climatic changes (including drought and ice ages);
d. e.g. meteorite impacts;
(Evolution)
e. Evolution is a natural factor that has led to increased biodiversity;
f. Mutation leads to increases in genetic diversity;
g. Natural selection may lead to some reduction in genetic diversity;
h. Speciation has led to increased species diversity;
i. Adaptive radiation has led to increased speciation/genetic diversity;
Human caused factor [4 max]:
(Extinction)
j. human activity is considered to be causing a sixth mass extinction; k. e.g. habitat destruction/deforestation/urbanisation;
I. e.g. pollution of freshwater water bodies/oceans/soils/atmosphere/leading to climate change/associated environmental hazards;
m. e.g. over-exploitation of resources/overfishing/hunting/intensive agriculture;
(Conservation)
n. conservation/restoration of ecosystems has led to increased biodiversity; o. e.g. establishment of national parks/nature reserves etc.; p. e.g. ex situ conservation/zoos/plantations/seed banks reduce loss of biodiversity; q. e.g. legislation/trade agreements protecting species e.g. CITES/fishing quotas/endangered species act;