Final answer:
Photosynthesis is reduced at low and high temperatures due to reduced enzyme activity at lower temperatures and decreased gas solubility, increased respiration, and stomatal closure at higher temperatures.
Step-by-step explanation:
The role of photosynthesis in plants is reduced at both low and high temperatures because temperature affects the activity of enzymes, which are proteins that speed up the chemical reactions in cells. At low temperatures, enzyme activity is reduced because the molecular movements are slower, leading to a decrease in the rate of photosynthetic reactions. In contrast, at high temperatures, while certain chemical reactions may speed up, the overall process of photosynthesis does not continue to increase due to factors such as the reduced solubility of carbon dioxide in water, increasing respiration rates, and a potential loss of water through increased transpiration which can lead to stomatal closure, further limiting carbon dioxide intake. Therefore, the most correct answer to the question is (A) Photosynthesis is hindered by extreme temperatures, impacting enzyme activity.
Specifically, the solubility of essential gases like carbon dioxide, necessary for the Calvin cycle in photosynthesis, decreases with higher temperatures, impacting the flow of this gas into the leaves. Moreover, at higher temperatures, plants may close their stomata to reduce water loss, which further limits carbon dioxide availability. This is in addition to the fact that at temperatures beyond a certain optimal point, the rate of respiration increases more than the rate of photosynthesis, leading to a decrease in net photosynthesis.