A student measures the rate of photosynthesis of a plant at 20°C and then again at 30°C, keeping light intensity and CO₂ concentration constant and non-limiting. Which result is most likely, and what is the best explanation?

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Question

A student measures the rate of photosynthesis of a plant at 20°C and then again at 30°C, keeping light intensity and CO₂ concentration constant and non-limiting. Which result is most likely, and what is the best explanation?

Accepted Answer

The rate is higher at 30°C because enzyme-controlled reactions proceed faster with increased temperature — Between 20°C and 30°C, enzyme activity increases with temperature (within the tolerance range of the enzymes), so the rate of photosynthesis increases. Option A is incorrect because enzyme denaturation occurs at significantly higher temperatures, typically above 40–45°C for most plant enzymes. Option B is incorrect because temperature, not just light intensity, is a limiting factor. Option D conflates increased respiration rate with a reduction in the measured rate of photosynthesis, but increased respiration does not directly reduce enzyme activity in the chloroplasts.

Answer

The rate is the same at both temperatures because light intensity has not changed

Answer

The rate is lower at 30°C because enzymes are denatured at higher temperatures

Answer

The rate is lower at 30°C because plants respire more at higher temperatures, using up glucose

Answer

The rate is higher at 30°C because enzyme-controlled reactions proceed faster with increased temperature

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