why would it be hard to find the ideal light intensity if the temperature were very hot or cold?

It is hard to find the ideal light intensity at very hot or very cold temperatures because temperature itself strongly limits biological activity, so changes in light no longer show a clear effect.

Basic idea

When temperature is far from an organism’s optimum, temperature becomes the main “bottleneck,” so even if light is adjusted perfectly, the process (like photosynthesis) still runs poorly. That makes it difficult to see which light level is truly best, because low performance is caused by temperature stress, not just light.

In terms of photosynthesis

• At very low temperatures , enzyme activity in photosynthesis slows down, so even high light cannot produce a high rate of photosynthesis. The graph of rate vs. light would look “flattened,” hiding the real optimum light intensity.

• At very high temperatures , enzymes can denature and membranes get damaged, so plants may shut down or suffer heat stress, again limiting photosynthesis even if light is ideal.

Why “ideal” is hard to see in an experiment

• Normally, to find ideal light intensity, you keep temperature constant and change only light, then look for the light level that gives the highest rate.

• If the temperature is very hot or cold, the organism is already stressed, so the measured rate is low at all light levels and the curve may never show a clear peak.

How you might phrase an answer on a worksheet

It would be hard to find the ideal light intensity because at very hot or very cold temperatures, temperature becomes the limiting factor, so the organism cannot reach its maximum rate of photosynthesis at any light level, making the “best” light intensity unclear.

Information gathered from public forums or data available on the internet and portrayed here.