Why is a suitable temperature necessary for the dark stage of photosynthesis?

Why is a suitable temperature necessary for the dark stage of photosynthesis?

• A. Controlled by enzymes
• B. Water supply controls it
• C. Depends on light intensity
• D. Unrelated to temperature

Answer: (A)

The dark stage relies on enzyme-driven chemical steps to convert CO2 into sugars, so temperature must be suitable to keep those enzymes working efficiently. Enzymes have an optimum temperature where their shapes and active sites function best; at that point the Calvin cycle runs at a rate that allows CO2 fixation to keep up with the use of ATP and NADPH from the light reactions. If the temperature drops too low, molecular movements slow and reaction rates fall, slowing the cycle. If the temperature rises too high, enzymes can lose their shape or become unstable, drastically reducing activity. Even though this stage doesn’t use light directly, it depends on the energy carriers produced by the light reactions, so the enzymes’ performance, and thus the cycle’s rate, is temperature-dependent. Water supply isn’t the direct driver of the dark stage, and while light intensity affects the amount of energy available, the key factor for the dark stage’s speed is how well the temperature supports the enzymes involved.

The dark stage relies on enzyme-driven chemical steps to convert CO2 into sugars, so temperature must be suitable to keep those enzymes working efficiently. Enzymes have an optimum temperature where their shapes and active sites function best; at that point the Calvin cycle runs at a rate that allows CO2 fixation to keep up with the use of ATP and NADPH from the light reactions. If the temperature drops too low, molecular movements slow and reaction rates fall, slowing the cycle. If the temperature rises too high, enzymes can lose their shape or become unstable, drastically reducing activity. Even though this stage doesn’t use light directly, it depends on the energy carriers produced by the light reactions, so the enzymes’ performance, and thus the cycle’s rate, is temperature-dependent. Water supply isn’t the direct driver of the dark stage, and while light intensity affects the amount of energy available, the key factor for the dark stage’s speed is how well the temperature supports the enzymes involved.