Explain how the change in mean number of capillaries can improve the athlete's performance.

Here are the solutions to the questions:

6. (a) (ii) State two ways in which the structure of blood vessel A differs from the structure of blood vessel J.
(Assuming A is the aorta and J is the pulmonary artery, based on previous context.)

1. Wall thickness and elasticity: Blood vessel A (aorta) has significantly thicker, more muscular, and more elastic walls than blood vessel J (pulmonary artery). This structural adaptation allows the aorta to withstand and maintain the very high blood pressure generated by the left ventricle and to smooth out blood flow.
2. Lumen diameter: Blood vessel A (aorta) generally has a larger lumen diameter than blood vessel J (pulmonary artery). This larger lumen allows it to carry the entire cardiac output to the systemic circulation efficiently.

6. (b) Explain how the change in mean number of capillaries can improve the athletic performance.

The data in Table 6.2 shows that after training, the mean number of capillaries per mm² in the muscle increased from 313 to 349. This increase in capillary density improves athletic performance in the following ways:

• Increased surface area for exchange: A higher number of capillaries provides a larger total surface area for the exchange of substances between the blood and the muscle cells.
• Enhanced oxygen supply: This larger surface area, combined with a shorter diffusion distance (capillaries are one cell thick), allows for more efficient and rapid diffusion of oxygen from the blood into the muscle cells. More oxygen means more efficient aerobic respiration, leading to greater ATP production for sustained muscle contraction and delayed fatigue.
• Faster waste removal: The increased capillary network also facilitates the more efficient and rapid removal of metabolic waste products such as carbon dioxide and lactic acid from the muscle cells. Preventing the accumulation of these waste products helps maintain optimal muscle function and reduces muscle fatigue.
• Improved nutrient delivery: More capillaries also mean a better supply of essential nutrients (like glucose) to the working muscles, supporting their energy demands during prolonged exercise.