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Date May 2019 Marks available 2 Reference code 19M.3.SL.TZ1.11
Level Standard level Paper Paper 3 Time zone Time zone 1
Command term Outline Question number 11 Adapted from N/A

Question

The table shows the distribution of four coral reef species along a transect as a function of depth.

[Source: © International Baccalaureate Organization 2019]

From the data, identify the depth along the transect where the greatest species richness is observed.

[1]
a.

Outline the relationship between Zooxanthellae and reef-building coral reef species.

[2]
b.

Suggest one way in which depth may act as a limiting factor for coral. 

[1]
c.

Markscheme

6.5 m ✔

Unit required

a.

a. a symbiotic/mutualistic relationship ✔

b. Zooxanthellae obtain shelter/habitat/exposure to light ✔

c. coral obtains energy/food through photosynthesis of the Zooxanthellae

b.

low light levels/lower temperatures cannot support growth/metabolism ✔

Requires the explanation for the mark

c.

Examiners report

Richness appeared well understood but the depth unit was sometimes omitted.

a.

This was a well-answered question with many candidates knowing the term symbiosis or mutualism. Protection provided by coral was often stated but the role of Zooxanthellae in providing nutrients from photosynthesis was less often seen.

b.

The reduction in light or temperature with greater depth was recognized but not often linked to growth or photosynthesis.

c.

Syllabus sections

Option C: Ecology and conservation » Option C: Ecology and conservation (Core topics) » C.4 Conservation of biodiversity
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Option C: Ecology and conservation » Option C: Ecology and conservation (Core topics)
Option C: Ecology and conservation

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