DP Biology (last assessment 2024)
Question 18M.3.HL.TZ2.15c
| Date | May 2018 | Marks available | [Maximum mark: 3] | Reference code | 18M.3.HL.TZ2.15c |
| Level | HL | Paper | 3 | Time zone | TZ2 |
| Command term | Explain | Question number | c | Adapted from | N/A |
c.
[Maximum mark: 3]
18M.3.HL.TZ2.15c
The interaction web shows top-down and bottom-up effects in a seagrass study system.
(c)
Explain how nutrients can have a positive or negative bottom-up effect on seagrass.
[3]
Markscheme
a. the positive «bottom up» effect is due to availability of nutrients
b. «nutrients» increase abundance/plant growth rates
c. the negative «bottom-up» effect as excess of nutrients causes a bloom in algae growth/eutrophication/competition
d. limited nutrients have negative effect on seagrass «growth»
e. «excess» algae cause seagrass to die/decompose/replenish nutrients
Do not accept answers referring to top down effects.
