Which organ removes the largest amount of excess water from the body?

1. Analyze the question The question asks which organ removes the largest amount of excess water from the body. This is about excretion and osmoregulation (water balance).

2. Explain the concept The body loses water in four main ways:

• Kidneys: remove excess water as urine (about 1-2 litres per day). This is the main route, and the amount is adjusted by the hormone ADH to keep the body's water balance.
• Skin: loses water as sweat, mostly to cool the body. This increases during hot weather or exercise.
• Lungs: lose water vapour when we breathe out, but only in small amounts.
• Liver: its main job is breaking down excess amino acids into urea, regulating blood sugar, and detoxifying. It does not remove water from the body.

3. Step-by-step solution

• Liver: it makes urea but does not eliminate water. Eliminated.
• Lung: removes only small amounts of water vapour. Eliminated.
• Skin: removes water as sweat, but the amount varies and is usually less than urine under normal conditions. Eliminated.
• Kidney: removes the largest volume of water, controlled by ADH to maintain osmotic balance. Correct.

4. Answer The correct option is C. Kidney.

5. Exam tip Remember: "Kidney = Key to water balance." When a question says "largest amount of water" or "osmoregulation," think kidney first. Skin is the answer only if the question mentions temperature regulation or sweating.