OCR General Certificate of Secondary Education (GCSE) Biology Practice Exam

How does temperature affect the rate of photosynthesis?

1. Increases at low temperatures and decreases at high temperatures

2. Decreases consistently with higher temperatures

3. Remains constant regardless of temperature

4. Slows down at low temperatures and denatures enzymes at high temperatures

The correct answer is: Slows down at low temperatures and denatures enzymes at high temperatures

The correct understanding of how temperature affects the rate of photosynthesis is that it slows down at low temperatures and can denature enzymes at high temperatures. Photosynthesis involves a series of enzyme-catalyzed reactions, and temperature plays a crucial role in these enzymatic processes. At low temperatures, kinetic energy decreases, which results in fewer collisions between the enzymes and the substrates (such as carbon dioxide and water). This slow movement leads to a reduced rate of photosynthesis because the enzymes are not working efficiently. As the temperature rises, the rate of photosynthesis initially increases due to higher kinetic energy, which enhances enzyme activity. However, if the temperature continues to rise too high, it can cause the enzymes to become denatured. This means that the structure of the enzyme changes, rendering it ineffective at catalyzing reactions. As a result, the rate of photosynthesis declines sharply as essential enzymes lose their functional shape. This characteristic response of enzymes to temperature highlights the importance of maintaining optimal conditions for photosynthesis, since both very low and very high temperatures can negatively impact the process.