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Date November 2016 Marks available 3 Reference code 16N.3.HL.TZ0.17
Level Higher level Paper Paper 3 Time zone TZ0 / no time zone
Command term Explain Question number 17 Adapted from N/A

Question

State two bottom-up factors affecting algal blooms.

[2]
a.

Explain how top-down factors control algal blooms.

[3]
b.

Markscheme

minerals
OR
nutrients
OR
phosphorus
OR
nitrogen

Award [1] to any two factors stated.

Accept abiotic factors such as temperature, light, pH, CO2 concentration.

a.

a. the herbivores / «first» consumers regulate algal bloom

b. predators of the herbivores help regulate algal bloom/reduce herbivore abundance/OWTTE

c. overfishing/death of predators/decreased reproduction of predators decreases algal bloom as herbivore population increases/OWTTE

Accept vice versa for marking point c.

d. habitat degradation can decrease algal bloom

e. pathogens of algae will decrease algal bloom
OR
alien/invasive species may compete for habitat and affect algal bloom/OWTTE

b.

Examiners report

[N/A]
a.
[N/A]
b.

Syllabus sections

Option C: Ecology and conservation » Option C: Ecology and conservation (Additional higher level topics) » C.5 Population ecology
Option C: Ecology and conservation » Option C: Ecology and conservation (Additional higher level topics)
Option C: Ecology and conservation

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