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Excretion in human beings and nephron

Excretion is the removal of metabolic wastes from the body, mainly through kidneys, lungs, skin, and liver.

In one line: Kidney filters, nephron fine-tunes, urine carries waste.

Understand it

The kidneys filter blood and remove urea, extra salts, and excess water as urine. Inside each kidney, nephrons perform filtration, reabsorption, and secretion. This keeps the blood composition balanced and prevents waste buildup.

Example

After drinking a lot of water, the body may produce more dilute urine to maintain balance.

Rule to remember

Rule: Blood is filtered, useful substances are reabsorbed, and wastes are passed out as urine.

See it worked out

Follow the example line by line, then use the same method on new questions.

Worked example

After a salty meal, the kidneys help remove extra salts and adjust water content so the body stays balanced.

Method you can reuse

1State waste removal.
2Name kidney and nephron.
3Describe filtration.
4Describe reabsorption.
5Mention urine output and balance.

Sketch it in your answer

Label glomerulus, Bowman's capsule, tubule, and collecting duct; show filtration and reabsorption arrows.

Check yourself

Answer the question in your head before opening the answer.

Try it yourself

Why is the nephron called the functional unit of the kidney?

Think first, then show answer

The nephron is called the functional unit of the kidney because it carries out filtration of blood, useful substance reabsorption, and urine formation.

Common wrong answer

Excretion means removing undigested food.

Why it loses marks: That is egestion; excretion removes metabolic waste.

Don't mix this up

Students think excretion is the same as egestion.

Exam tip

In answers, use the words filtration, reabsorption, and urine formation.

Write it in the exam

Each point is worth about one mark. Write point 1 for a 1-mark question and keep adding points as the marks go up.

How CBSE asks it

Draw a nephron, explain urine formation, or differentiate excretion and egestion.

1
Enough for 1 mark
Excretion is the removal of metabolic wastes from the body, mainly through kidneys, lungs, skin, and liver.
2
Add for 2 marks
Example: After drinking a lot of water, the body may produce more dilute urine to maintain balance.
3
Add for 3 marks
The kidneys filter blood and remove urea, extra salts, and excess water as urine.

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