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

Which of the following can be considered a limiting factor for photosynthesis?

1. Soil quality

2. Wind speed

3. Temperature

4. Plant age

The correct answer is: Temperature

In the context of photosynthesis, temperature plays a crucial role in influencing the rate at which the process occurs. Photosynthesis is fundamentally a biochemical reaction that depends on the efficiency of enzymes involved in converting carbon dioxide and water into glucose and oxygen using light energy. When the temperature is within an optimal range, the enzymes function effectively. However, if the temperature is too low, enzyme activity slows down, leading to a reduced rate of photosynthesis. Conversely, if the temperature exceeds a certain threshold, enzymes can denature (lose their functional shape), leading to a rapid decline in the rate of photosynthesis. Hence, temperature is a key factor that can limit the process of photosynthesis under varying environmental conditions. While soil quality, wind speed, and plant age can influence plant growth and health, they are not direct limiting factors specifically for the photosynthetic process itself in the same manner as temperature. Soil quality affects nutrient availability, wind speed can impact transpiration and water loss, and plant age relates to overall maturity and plant structure, but it is temperature that directly influences the biochemical reactions taking place during photosynthesis.