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

What can affect the rate of respiration?

1. Only temperature

2. pH and substrate concentration

3. Temperature and light intensity

4. Temperature and pH

The correct answer is: Temperature and pH

The rate of respiration is influenced by several factors, one of which is temperature. Higher temperatures generally increase the kinetic energy of molecules, leading to faster reaction rates, up to a certain point where enzymes may denature. This makes temperature a crucial factor in respiration. Additionally, pH levels play a significant role because enzymes that facilitate respiration are sensitive to changes in acidity or alkalinity. If the pH strays too far from the optimal range, the enzymes can become less effective or inactive, which would slow down the respiration rate. In combination, temperature and pH both regulate enzymatic activity and metabolic processes, making them integral to the rate of respiration in cells. This is why the inclusion of both temperature and pH as factors affecting respiration is the most accurate choice in this context.