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

What is the role of mitochondria in both animal and plant cells?

1. Photosynthesis

2. Synthesis of proteins

3. Respiration and energy release

4. Aids in cell division

The correct answer is: Respiration and energy release

Mitochondria play a crucial role in both animal and plant cells primarily through their involvement in respiration and energy release. They are often referred to as the "powerhouses" of the cell due to their function in generating adenosine triphosphate (ATP), which is the primary energy currency of cells. During cellular respiration, mitochondria convert biochemical energy from nutrients into ATP through a series of metabolic processes, including the Krebs cycle and oxidative phosphorylation. This process requires oxygen and is vital for the survival and functioning of all aerobic organisms. The energy produced in the form of ATP is used for various cellular activities, including muscle contraction, synthesis of biomolecules, and active transport across cell membranes. The other options relate to different cellular processes. Photosynthesis is primarily a function of chloroplasts in plant cells, where light energy is converted into chemical energy. The synthesis of proteins occurs on ribosomes, not mitochondria. Although mitochondria play some role in cell division indirectly due to their energy supply, they are not directly involved in the process itself. Hence, the primary role of mitochondria is best captured in the context of respiration and energy release.