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IB Biology HL C4.1.6 Negative Feedback Control Questions

Interpret predator, disease, competition and resource evidence to explain how density-dependent negative feedback stabilizes or reduces populations in IB Biology HL C4.1.6.

Syllabus
First assessment 2025
Course
Biology HL
Level
HL

Exam points

  • Explain density-dependent negative feedback: as population density rises, competition, predation, disease, parasitism or waste intensifies, reducing natality or increasing mortality.
  • Interpret population data or growth-curve changes to identify the limiting biotic factor and link its density-dependent action to stabilization or decline.

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Study C4.1.6—Negative feedback control conceptsOpen the corresponding Concept lesson for explanations, examples and exam connections.

IB Biology HL C4.1.6 Negative Feedback Control Questions question 1

[Maximum number: 2]

The prickly pear cactus (Opuntia stricta) was first recorded in Kruger National Park, South Africa, in 1950 . It spread rapidly, mainly through seeds being dispersed by baboons and elephants.

In 1997, the cactus moth (Cactoblastis cactorum) from South America was introduced into the area as a biological control. The larvae of the moth feed on the cactus. The graph shows the number of cladodes (flattened stem sections) of cactus found per m2\mathrm{m}^{2} in the years before and after the introduction of the cactus moth.

Figure for Question IB Biology HL C4.1.6 Negative Feedback Control Questions question 1 — IB Biology HL

Explain the change in numbers of the cactus moth throughout the study period.

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