2. Read the extract below and answer the questions that follow.

Cellular respiration is the process in which cells use oxygen to produce ATP. During exercise, muscle cells have to work harder, which increases their demand for oxygen, thus increasing breathing and heart rate to help increase the oxygen in the bloodstream. During high-speed athletics, the oxygen supply is less than the demand; therefore, muscles begin converting glucose into lactic acid instead of energy. At the end of the race, athletes have to breathe deeper and faster.

Aerobic and anaerobic respiration are used to supply energy during exercise.

During certain types of exercise, for example, athletic 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 the fraction of the oxygen required, and the body goes into 'oxygen debt'. 'Oxygen debt' can be defined as the extra oxygen needed to normalize the process after strenuous exercise. This debt can only be repaid by rapid breathing after the sprint ends.

2.1 Name:
(a) The type of cellular respiration that does not rely on oxygen to take place.
(b) TWO end products of aerobic respiration in muscle cells of animals.
(c) The athletic event that relies the most on anaerobic respiration.

2.2 Explain your answer to QUESTION 2.1(c) above.

2.3 Describe what happens to the energized hydrogen atoms released during aerobic respiration.

2.4 An athlete runs very fast for 200m, then stops running. His breathing rate and heart rate remain high for several minutes. Explain why this happens.

2.5 Tabulate TWO differences between aerobic and anaerobic respiration.

In a 100m sprint, the athlete exerts maximum effort in a short period of time requiring immediate energy. During such high-intensity, short-duration activities, oxygen cannot be delivered to the muscles quickly enough to meet the high energy demand, prompting reliance on anaerobic respiration which does not require oxygen and is faster at producing energy.

2.3 Describe what happens to the energized hydrogen atoms released during aerobic respiration:

During aerobic respiration, energized hydrogen atoms are initially carried by electron carriers, such as NAD⁺ and FAD. These carriers transport the hydrogen atoms to the electron transport chain, located in the mitochondria, where the hydrogen electrons participate in a series of reactions that ultimately result in the production of ATP and water as a final product.

2.4 An athlete runs very fast for 200m then he stops running. His breathing rate and heart rate remain high for several minutes. Explain why this happens:

After the 200m sprint, the athlete's body has accumulated an 'oxygen debt' due to the high demand for energy that exceeded the supply of oxygen during the sprint. The elevated breathing rate and heart rate are the body's mechanisms to supply additional oxygen to clear lactic acid, replenish depleted energy stores, and restore normal metabolic conditions in the muscle cells.

2.5 Tabulate TWO differences between aerobic and anaerobic respiration:

Aerobic RespirationAnaerobic RespirationOccurs in the presence of oxygenOccurs in the absence of oxygenProduces carbon dioxide and water as end productsProduces lactic acid (in animals) as the end productYields more ATP (about 36-38 ATP molecules)Yields less ATP (about 2 ATP molecules)