CourseCourseConceptConceptDocsDocuments

IB Biology HL D4.2.5 Keystone Species Questions

Analyse disproportionate keystone effects, top-down cascades and biodiversity changes in ecological communities.

Syllabus
First assessment 2025
Course
Biology HL
Level
HL

Exam points

  • Define or identify a keystone species by its disproportionate effect on community structure relative to abundance.
  • Explain top-down effects and trophic cascades when a keystone species is present, removed or protected, including changes in algae, populations and biodiversity.

Learn this topic

Study D4.2.5—Keystone species conceptsOpen the corresponding Concept lesson for explanations, examples and exam connections.

IB Biology HL D4.2.5 Keystone Species Questions question 1

[Maximum number: 2]

The gut of a healthy human contains more than 1000 species of bacteria. Some of these species are shown in the cladogram.

Figure for Question IB Biology HL D4.2.5 Keystone Species Questions question 1 — IB Biology HL

Scientists have found that B. fragilis and B. stercosis are keystone species in the human gut ecosystem.

Define keystone species.

All question bank results loaded