(a) Sometimes while running, the athletes suffer from muscle cramps. Why? How is the respiration in this case different from aerobic respiration? OR (b) Write the other name given to lymph. State its two functions.

(a)

During sudden or vigorous physical activities like running, our muscle cells require a large amount of energy quickly. Since the supply of oxygen to meet this demand is insufficient, anaerobic respiration takes place in the muscle cells. Under these conditions of lack of oxygen, pyruvate is converted into lactic acid (a 3-carbon molecule). The accumulation of lactic acid in the muscles causes muscle cramps.

Difference between this respiration (anaerobic in muscles) and aerobic respiration:

1. Oxygen Requirement: Respiration in muscles during cramps occurs in the lack of oxygen (anaerobic), whereas aerobic respiration occurs in the presence of oxygen.
2. End Products: Respiration in muscles produces lactic acid and a small amount of energy, whereas aerobic respiration completely breaks down glucose into carbon dioxide ($\text{CO}_2$), water ($\text{H}_2\text{O}$), and releases a much larger amount of energy.

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OR

(b)

Other name for lymph:

Lymph is also known as tissue fluid.

Two functions of lymph:

1. It carries digested and absorbed fat from the intestine.
2. It drains excess fluid from the extracellular space back into the blood.