| 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.
Explain how top-down factors control algal blooms.
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. 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
Examiners report
Syllabus sections
- 17N.3.HL.TZ0.15b: State how the population of M. gallopavo may have been determined.
- 19M.3.SL.TZ1.11c: Suggest one way in which depth may act as a limiting factor for coral.
-
16N.3.HL.TZ0.17a:
State two bottom-up factors affecting algal blooms.
- 18M.3.SL.TZ1.12c: State one method that could be used to estimate the isopod population size.
-
19M.3.HL.TZ2.16a:
Explain the factors that can contribute to the exponential growth phase in a sigmoid population curve.
- 16N.3.HL.TZ0.16a: Describe one method that could have been used to estimate the population size of a given tree...
- 17N.3.HL.TZ0.15a.i: State the range of years when exponential growth of the M. gallopavo population occurred.
- 18M.3.HL.TZ1.17a.ii: Suggest one possible cause for the decrease of the number of animals after 1940.
- 16N.3.SL.TZ0.14a: Outline the trend in the number of people with malaria during the period when the use of...
- 17M.3.HL.TZ2.15e: Explain how an excessive growth of algae on coral reefs can be controlled by top-down factors.
- 18M.3.HL.TZ2.15c: Explain how nutrients can have a positive or negative bottom-up effect on seagrass.
- 18M.3.HL.TZ1.17a.i: State the type of growth of this population up to 1940.
- 17M.3.HL.TZ1.17: Discuss the factors affecting population growth that can result in an exponential growth curve.
-
19N.3.HL.TZ0.18:
Explain the technique used to estimate the population size of a named species of organism that is able to move.
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19M.3.HL.TZ1.19:
The garden snail, Helix aspersa, is a herbivore.
[Source: Sinan Önder /https://www.pexels.com/photo/animal-close-up-crawling-garden-243128/]
Explain how the population of snails in an ecosystem could be estimated by capture-mark-release-recapture, identifying the limitations in the method.
- 19M.3.HL.TZ2.16b: Outline the effect of carrying capacity on the growth of a population.
-
17N.3.HL.TZ0.15a.ii:
Suggest factors that could account for the growth curve of the M. gallopavo population.
-
17N.3.HL.TZ0.15c:
Hunting of M. gallopavo is currently regulated. Predict what would happen if the hunting regulations were removed.
