Question 19 of 33intermediate💡 UnderstandLong Answer5 marks

Describe the structure and functioning of nephrons.

Correct Answer

Nephrons are the basic filtration units in the kidneys, packed close together in large numbers. Their primary function is to remove nitrogenous waste such as urea or uric acid from the blood.

Structurally, a nephron consists of a cluster of very thin-walled blood capillaries. This cluster is associated with the cup-shaped end of a coiled tube called Bowman’s capsule, which collects the filtrate.

Functioning involves the initial filtration of blood in the capillary cluster. As the filtrate flows along the tube, useful substances are selectively re-absorbed. These substances include glucose, amino acids, salts, and a major amount of water.

The amount of water re-absorbed depends on how much excess water is in the body and the amount of dissolved waste to be excreted. This regulation ensures that essential nutrients are retained while waste is removed.

Finally, the volume of urine is significantly reduced by re-absorption. In a healthy adult, the initial filtrate is about 180 L daily, but the actual volume excreted is only a litre or two a day because the remaining filtrate is re-absorbed in the kidney tubules.

Exercise: QUESTIONS | Q: 1 | (Page 20)
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Explanation

The answer is constructed strictly from the provided context, which describes nephrons as filtration units consisting of a capillary cluster and Bowman's capsule. It highlights the process of selective re-absorption of glucose, amino acids, salts, and water. The explanation adheres to the word count and paragraph constraints for a 5-mark long answer question.

Solution Steps

  1. Step 1: Define nephrons as the basic filtration units packed in the kidneys.

  2. Step 2: Describe the structure: a cluster of thin-walled blood capillaries associated with Bowman’s capsule.

  3. Step 3: Explain the functioning: Filtration of nitrogenous waste followed by selective re-absorption of glucose, amino acids, salts, and water.

  4. Step 4: Detail the regulation of water re-absorption based on the body's needs.

  5. Step 5: Conclude with the quantitative aspect of filtration (180 L initial vs 1-2 L excreted) to demonstrate re-absorption efficiency.

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