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

What is the ideal temperature for photosynthesis to occur efficiently?

1. 20 degrees

2. 30 degrees

3. 35 degrees

4. 45 degrees

The correct answer is: 45 degrees

The ideal temperature for photosynthesis to occur efficiently is generally around 30 degrees Celsius. At this temperature, the enzymes that facilitate the photosynthesis process, such as RuBisCO, are optimized for activity, allowing for a high rate of carbon fixation and energy production. While temperatures higher than 30 degrees can initially enhance the rate of photosynthesis, they can also lead to stress on the plant. At temperatures around 35 degrees, some plants may still function well, but if temperatures continue to rise towards 45 degrees, a significant drop in efficiency can occur due to enzyme denaturation and increased transpiration rates. In essence, while plants might endure brief periods of higher temperatures, sustained heat above optimal levels can be detrimental to the overall photosynthetic process. In contrast, lower temperatures, such as 20 degrees, may not provide enough energy for the reactions involved in photosynthesis, thus leading to reduced efficiency. Therefore, while the answer suggests an optimal temperature for efficient photosynthesis includes 20 degrees, 30 degrees is more aligned with scientific consensus as the ideal temperature range for photosynthesis to function optimally.