Question

Above 38oC and below 0oC the rate of photosynthesis decreases. Propose a hypothesis to explain why this occurs.


A: Enzyme activity decreases at these temperatures
B: At these temperatures plants wilt
C: Chlorophyll cannot absorb energy from the sun at these temperatures
D: The cytoplasm of the plant cell cannot function

Answer 1

The right answer is A: Enzyme activity decreases at these temperatures

Temperature influences the activity of the enzymes responsible for assisting with chemical reactions in the Calvin cycle. When temperatures are low, enzyme activity is slow. As temperatures increase, the activity of the enzymes that assist in these chemical reactions also increases to a certain extent, which is the optimal response to temperature. It is at this point that the rate of photosynthesis of plants is the highest.

As the temperature continues to rise beyond this point, the enzyme activity decreases until photosynthesis stops. It is important to remember that the rate of photosynthesis in C3 plants is higher in cold conditions, whereas it is the opposite in C4 plants.