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

What type of reaction is respiration classified as?

1. Endothermic

2. Exothermic

3. Isothermic

4. Catabolic

The correct answer is: Exothermic

Respiration is classified as an exothermic reaction because it involves the release of energy. During respiration, organic molecules, primarily glucose, are broken down in the presence of oxygen to produce carbon dioxide, water, and energy in the form of ATP (adenosine triphosphate). This process releases energy stored in the chemical bonds of glucose, making it available for cellular activities. The energy transformation in respiration is a fundamental process that cells utilize to fuel various functions such as growth, repair, and maintenance. In contrast, an endothermic reaction would absorb energy, which is not the case in respiration. The terms isothermic and catabolic offer additional context but do not directly characterize the energy aspect of the reaction as clearly as exothermic does. While catabolic refers to the breakdown of larger molecules into smaller ones, which indeed occurs during respiration, labeling it exothermic captures the energy release component more specifically.