A graph shows the rate of photosynthesis against temperature. The rate increases from 10°C to 35°C, then sharply decreases above 40°C. What best explains the decrease above 40°C?

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Question

A graph shows the rate of photosynthesis against temperature. The rate increases from 10°C to 35°C, then sharply decreases above 40°C. What best explains the decrease above 40°C?

Accepted Answer

Enzymes controlling photosynthesis denature at higher temperatures — Above about 40°C, the enzymes involved in photosynthesis (such as RuBisCO) begin to denature — their active sites change shape permanently, reducing the rate sharply. Chlorophyll stability is not the primary reason for the sharp decline. CO₂ solubility decreasing is a minor effect, not the main cause of the sharp drop shown. Stomata control gas exchange, not light entry.

Answer

Stomata close at higher temperatures, blocking light entry

Answer

Chlorophyll absorbs less light at higher temperatures

Answer

Carbon dioxide becomes less soluble at higher temperatures

Answer

Enzymes controlling photosynthesis denature at higher temperatures

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