Question 21M.2.SL.TZ2.b
| Date | May 2021 | Marks available | [Maximum mark: 1] | Reference code | 21M.2.SL.TZ2.b |
| Level | SL | Paper | 2 | Time zone | TZ2 |
| Command term | State | Question number | b | Adapted from | N/A |
The mass of an individual organism can affect its physiology and feeding ecology. The diagram shows the relative mass of carbon (black) and total wet mass (grey) of a marine crustacean, Calanus hyperboreus and a jellyfish, Bathocyroe fosteri.
[Source: Kristian McConville, Angus Atkinson, Elaine S. Fileman, John I. Spicer, Andrew G. Hirst. Disentangling the counteracting effects of water content and carbon mass on zooplankton growth. Journal of Plankton Research. 2017, Volume 39, Issue 2, Pages 246–256. https://doi.org/10.1093/plankt/fbw094. Adapted (and translated) by permission of Oxford University Press.]
The crustacean and the jellyfish obtain carbon compounds by feeding. State one source of carbon for marine organisms, other than feeding.
[1]
a. photosynthesis ✔
b. absorption of (dissolved) carbon dioxide / (hydrogen)carbonate directly from the oceans ✔
Accept reference to carbonate or hydrogencarbonate ions.
In 4(a) most were able to state 'respiration' as the answer. 4(b) proved more difficult with fewer stating photosynthesis or absorption of dissolved CO2 or HCO3 from the seawater. Vague answers such as 'carbon in the water' were not credited. In 4(c) most knew that energy enters with sunlight, but did not state photosynthesis. They knew that it was transferred by feeding through the trophic levels and lost as heat due to respiration. A surprising number incorrectly stated that the energy was recycled and some drew diagrams of the energy flow showing this. In 4(d)(i) most were able to state that the crustacean was a richer source of carbon. An explanation using the data from the diagram was expected. In 4(d)(ii) most were able to present an argument for advantage or disadvantage.
