| Date | November 2016 | Marks available | 2 | Reference code | 16N.3.HL.TZ0.17 |
| Level | Higher level | Paper | Paper 3 | Time zone | TZ0 |
| Command term | State | 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
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