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IB Biology HL C4.1.17 Top Down Vs Bottom Up Control Questions

Analyse mesocosm, seagrass and algal-bloom evidence to distinguish predator-driven top-down effects from nutrient-driven bottom-up control in IB Biology HL C4.1.17.

Syllabus
First assessment 2025
Course
Biology HL
Level
HL

Exam points

  • Distinguish top-down control by consumers or predators from bottom-up control by nutrients, producers or resource availability.
  • Interpret mesocosm or food-web data to trace direct and indirect effects across trophic levels, including algal blooms, seagrass and bacterial populations.
  • Evaluate how predator loss, overfishing or nutrient enrichment changes community structure through a trophic cascade.

IB Biology HL C4.1.17 Top Down Vs Bottom Up Control Questions question 1

[Maximum number: 3]

An investigation into food web interactions was conducted in mesocosms in the Mediterranean Sea, off the coast of France. The effects of the addition of soil and fish on bacterial populations were tested.

Figure for Question IB Biology HL C4.1.17 Top Down Vs Bottom Up Control Questions question 1 — IB Biology HL
Figure for Question IB Biology HL C4.1.17 Top Down Vs Bottom Up Control Questions question 1 — IB Biology HL

Question (a)

(a)

Assuming that the populations of bacteria are under bottom-up control, identify the mesocosms in which the bacterial populations will be highest.

[ 1 ]

Question (b)

(b)

Outline top-down effects on the bacteria in the four mesocosms.

[ 2 ]
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