(a) State the purpose of formation of urine.

(b) What will happen if there is no tubular reabsorption in the nephrons of kidney?

Life Processes

Excretion

Official Answer

(a) The purpose of urine formation is to filter out toxic nitrogenous waste products, such as urea and uric acid, from the blood and discard them from the body.

(b) If there is no tubular reabsorption in the nephrons, useful substances present in the initial filtrate—such as glucose, amino acids, salts, and a major amount of water—will not be reclaimed back into the blood. This would result in the loss of massive amounts of water (nearly $180\text{ L}$ of daily filtrate) and essential nutrients, leading to rapid dehydration, extreme drop in blood pressure, and ultimately death.

nitrogenous wasteureauric acidtubular reabsorptionglucoseamino acidswater lossdehydration

Marking Scheme

11 Mark: Stating that the purpose of urine formation is to filter out nitrogenous wastes (urea, uric acid) from the blood.
22 Marks: Explaining that without tubular reabsorption, essential substances (glucose, amino acids, salts) and a huge volume of water would be lost, causing fatal dehydration.

Hint

Think about what useful substances are filtered out initially and how much water would be lost if not reclaimed.

Quick Oral Answer

The purpose of urine formation is to remove toxic nitrogenous wastes like urea from the blood. If tubular reabsorption did not occur, we would lose essential nutrients like glucose and up to 180 liters of water daily, leading to fatal dehydration.

Analysis & Explanation

Urine formation is a vital homeostatic process. The glomerulus filters about $180\text{ L}$ of fluid daily in an adult human, but only about $1\text{ to }2\text{ L}$ is excreted as urine. This is because the rest of the filtrate is selectively reabsorbed as it flows along the renal tubule. Essential solutes like glucose, amino acids, and ions, along with water, are actively and passively transported back into the surrounding capillaries. Without tubular reabsorption, the body would suffer catastrophic fluid and nutrient depletion within hours.

Common Mistakes

1Stating that the purpose of urine is just to remove excess water, ignoring nitrogenous wastes.
2Failing to mention specific substances reabsorbed like glucose, amino acids, and water.

Interesting Facts

The human kidneys filter the entire blood volume about 60 times a day! This is why tubular reabsorption is absolutely critical to prevent us from drying out instantly.

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Frequently Asked Questions

How many marks does this question carry in CBSE Class 10 Science 2014?

This question carries 3 marks in the CBSE Class 10 Science 2014 examination.

Which chapter does this question come from in Science?

This question is from the chapter "Life Processes" in the CBSE Class 10 Science syllabus.

What topic does this question cover in Science?

This question covers the topic "Excretion" from CBSE Class 10 Science.

What type of question is this in the CBSE Class 10 Science 2014 paper?

This is a Short Answer question from Section SECTION-A in the CBSE Class 10 Science 2014 paper.