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

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What happens during aerobic respiration?

  1. Energy is produced without oxygen

  2. Energy is produced when oxygen is not available

  3. Energy is produced in the presence of plenty of oxygen

  4. Energy is produced regardless of oxygen levels

The correct answer is: Energy is produced in the presence of plenty of oxygen

During aerobic respiration, energy is produced in the presence of plenty of oxygen. This process occurs mainly in the mitochondria of cells, where glucose and oxygen are combined to produce energy, carbon dioxide, and water. The overall reaction can be summarized as glucose + oxygen → carbon dioxide + water + energy (in the form of ATP). The presence of oxygen is crucial for this type of respiration as it allows for complete oxidation of glucose, resulting in a higher yield of ATP compared to anaerobic respiration. In aerobic conditions, cells maximize the energy extracted from glucose through a series of biochemical pathways including glycolysis, the citric acid cycle (Krebs cycle), and oxidative phosphorylation. This makes aerobic respiration the most efficient form of energy production for cells, especially in metabolically active tissues.

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