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

In which process is glucose primarily used to release energy?

1. Photosynthesis

2. Respiration

3. Transpiration

4. Fermentation

The correct answer is: Respiration

Glucose is primarily used in respiration to release energy. This process occurs in the cells of living organisms, where glucose is broken down in the presence of oxygen to produce adenosine triphosphate (ATP), the energy currency of the cell. During respiration, glucose undergoes a series of metabolic reactions that ultimately convert it into carbon dioxide and water, releasing energy in the form of ATP that cells can use for various functions like growth, repair, and maintaining homeostasis. Photosynthesis, on the other hand, is the process by which plants, algae, and some bacteria convert light energy into chemical energy stored in glucose, rather than releasing energy from glucose itself. Transpiration is a process related to water movement in plants, where water evaporates from the plant leaves, and does not involve glucose or energy release. Fermentation is an alternative pathway to extract energy from glucose when oxygen is not available, but it does not occur as the primary process in most aerobic organisms. Therefore, respiration is the main process associated with the release of energy from glucose.