User interface language: English | Español

Date May 2018 Marks available 2 Reference code 18M.3.HL.TZ2.15
Level Higher level Paper Paper 3 Time zone Time zone 2
Command term Describe Question number 15 Adapted from N/A

Question

The interaction web shows top-down and bottom-up effects in a seagrass study system.

Identify which of the types of interaction shown in the key occur between crabs and seagrass.

[2]
a.

Describe how the sea otter indirectly affects seagrass.

[2]
b.

Explain how nutrients can have a positive or negative bottom-up effect on seagrass.

[3]
c.

Markscheme

a. indirect 

b. negative «effect» 

c. top-down

a.

a. sea otters have a positive «indirect» effect as sea otters feed on crabs that feed on isopods that feed on algae 

b. less crabs means more isopods so less algae 

c. less algae means more seagrass
OR
less competition between algae and seagrass

b.

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.

c.

Examiners report

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

Syllabus sections

Option C: Ecology and conservation » Option C: Ecology and conservation (Core topics) » C.1 Species and communities
Show 44 related questions
Option C: Ecology and conservation » Option C: Ecology and conservation (Core topics)
Option C: Ecology and conservation

View options