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

Why do plants sometimes have to resort to anaerobic respiration?

1. In the presence of high light intensity

2. When the soil is nutrient-rich

3. If the soil is water-logged

4. During periods of high temperature

The correct answer is: If the soil is water-logged

Plants resort to anaerobic respiration particularly when the soil is water-logged. This condition leads to low levels of oxygen availability in the soil, which is crucial for aerobic respiration. When roots are submerged in water, they can't efficiently take in oxygen from the soil, forcing the plant to switch to anaerobic respiration to produce energy. Anaerobic respiration allows for energy production without the need for oxygen but is less efficient and produces by-products such as alcohol or lactic acid, which can be harmful to the plant if accumulated. The other conditions mentioned, such as high light intensity, nutrient-rich soil, or high temperatures, do not directly cause a shift to anaerobic respiration. High light intensity and nutrient-rich conditions generally enhance aerobic respiration, while high temperatures affect the rate of respiration but do not typically limit oxygen availability.