AP Biology 4.4 Feedback and Homeostasis
Practise AP Biology 4.4 questions by connecting positive and negative feedback with hormone regulation and the maintenance of physiological set points.
- Syllabus
- Effective Fall 2025
- Course
- AP Biology
Exam points
- distinguish positive feedback amplification from negative feedback return toward a set point
- trace hormone or physiological feedback from stimulus to a homeostatic outcome
- use pathway data to predict changes in stimulus, hormone level or response
Covered syllabus points
4.4 Feedback question 1
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 describes the production of DMSP by coral and coral symbionts?
A
A negative feedback mechanism that increases the environmental change
B
A negative feedback mechanism that reverses the environmental change
C
A positive feedback mechanism that increases the environmental change
D
A positive feedback mechanism that reverses the environmental change
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