Read the extract below and answer the questions that follow:

Aerobic and anaerobic respiration are used to supply energy during exercise. During certain types of exercise, for example, athletics events such as 100m, 200m, 1500m, and 3000m, the muscles are unable to obtain sufficient oxygen for the removal of large quantities of lactic acid from their cells. When sprinting, an athlete cannot possibly inhale more than a fraction of the oxygen required, and the body goes into 'oxygen debt'. This debt can only be repaid by rapid breathing after the sprint ends.

3.2.1 Which athletic event relies the most on anaerobic respiration? (1)

3.2.2 Explain your answer in QUESTION 3.2.1 above. (2)

3.2.3 Name TWO end products of aerobic respiration in muscle cells. (2)

3.2.4 Explain what you understand by the term 'oxygen debt'. (2)

3.2.5 Tabulate TWO differences between aerobic and anaerobic respiration.

Anaerobic respiration is the dominant energy source in short, intense bursts of activity like a 100m sprint because these activities require a rapid supply of energy when the oxygen supply is limited. During a sprint, athletes need energy quickly, and the body cannot take in enough oxygen to meet the needs. So, it uses anaerobic respiration, which does not rely on oxygen, to produce energy.

3.2.3 Name TWO end products of aerobic respiration in muscle cells.

The two end products of aerobic respiration in muscle cells are carbon dioxide (CO₂) and water (H₂O).

3.2.4 Explain what you understand by the term 'oxygen debt'?

'Oxygen debt' refers to the amount of extra oxygen the body needs to restore itself to its normal metabolic function after strenuous activity. During intense exercise, lactic acid builds up due to anaerobic respiration. Once the exercise stops, the body continues to breathe rapidly to take in extra oxygen needed to convert lactic acid back into pyruvate and restore the balance of ATP and other energy stores.

3.2.5 Tabulate TWO differences between aerobic and anaerobic respiration.

Aerobic RespirationAnaerobic RespirationRequires oxygen to produce energy.Does not require oxygen to produce energy.Produces more energy (approximately 36 ATP).Produces less energy (approximately 2 ATP).End products are carbon dioxide and water.End product is lactic acid in muscle cells.