Practise AP Biology 8.2.D questions by tracing how autotrophs capture energy and heterotrophs transfer it through ecosystem food webs.
Questions 12-17 Certain reef-building corals contain photosynthetic, symbiotic algae that have the ability to make dimethylsulphoniopropionate (DMSP), a chemical involved in the marine sulfur cycle. DMSP is released into the surrounding water, where it is converted to the gas dimethyl sulfide (DMS) by microorganisms and enters the atmosphere. Once in the atmosphere, it triggers the formation of sulfate aerosols, which induce cloud formation and block sunlight from heating up the water. The symbiotic algae produce DMSP when they are stressed by a high water temperature. If water temperature is too high, corals will expel the symbiotic algae that produce DMSP. Researchers measured the amount of DMSP produced by juvenile and adult coral and their symbionts under normal and thermally stressed conditions. The data are shown in the graphs in Figure 1.
Figure 1: DMSP concentration in juvenile and adult corals and their symbionts in normal and thermally-stressed conditions. Error bars represent \(\pm 2 \mathrm{SE}_{x}\)
The researchers also measured the density of the symbiont as well as the photosynthetic yield in adult corals at the two temperatures. Photosynthetic yield is an index measure of energy output compared to sunlight energy input in which larger photosynthetic yield values represent photosynthetic organisms producing more energy.
Figure 2: Variation in symbiont density and photosynthetic yield in adult corals grown in normal and thermally-stressed conditions. Error bars represent \(\pm 2 \mathrm{SE}_{x}\)
Which of the following best explains the result of adult corals being exposed to elevated temperatures for extended periods?
They are able to obtain more energy from their symbionts because the algae are receiving more light.
They are able to obtain more energy from their symbionts because the efficiency increases slightly over time.
They are able to obtain less energy from their symbionts because the algae have been expelled.
They are able to obtain less energy from their symbionts because more DMSP is being produced at lower temperatures.