Question 19M.3.SL.TZ1.11
| Date | May 2019 | Marks available | [Maximum mark: 4] | Reference code | 19M.3.SL.TZ1.11 |
| Level | SL | Paper | 3 | Time zone | TZ1 |
| Command term | Identify, Outline, Suggest | Question number | 11 | Adapted from | N/A |
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]
6.5 m ✔
Unit required
Richness appeared well understood but the depth unit was sometimes omitted.
Outline the relationship between Zooxanthellae and reef-building coral reef species.
[2]
a. a symbiotic/mutualistic relationship ✔
b. Zooxanthellae obtain shelter/habitat/exposure to light ✔
c. coral obtains energy/food through photosynthesis of the Zooxanthellae ✔
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.
Suggest one way in which depth may act as a limiting factor for coral.
[1]
low light levels/lower temperatures cannot support growth/metabolism ✔
Requires the explanation for the mark
The reduction in light or temperature with greater depth was recognized but not often linked to growth or photosynthesis.