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

What is the main role of mitochondria in cells?

1. Photosynthesis occurs here

2. They store energy in the form of fat

3. Aerobic respiration takes place here

4. They are responsible for protein synthesis

The correct answer is: Aerobic respiration takes place here

Mitochondria are often referred to as the "powerhouses" of the cell due to their primary role in producing energy through a process known as aerobic respiration. This process involves breaking down glucose and oxygen to generate adenosine triphosphate (ATP), which is the main energy currency of the cell. The significance of this function cannot be overstated, as ATP is crucial for powering various cellular activities, including muscle contraction, active transport, and biosynthesis. In aerobic respiration, the mitochondria utilize enzymes and the electron transport chain to efficiently convert energy stored in glucose molecules into ATP. This process also produces carbon dioxide and water as byproducts. The ability of mitochondria to perform this complex function underscores their essential role in cellular metabolism and energy production, particularly in eukaryotic cells, where energy demands are high. The other options pertain to different cellular processes and structures. For instance, photosynthesis occurs in chloroplasts, which are present in plant cells, while energy storage in the form of fat is managed by adipocytes and does not occur directly in mitochondria. Similarly, protein synthesis primarily takes place in ribosomes, either free in the cytoplasm or attached to the endoplasmic reticulum. Hence, the unique