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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.

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Student-friendly explanation

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.

How to write this in exams

  1. 1

    Start with the exact idea

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

  2. 2

    Then show how to use it

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

  3. 3

    Add one concrete example

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

  4. 4

    Avoid this incomplete answer

    Excretion means removing undigested food. This is wrong because that is egestion; excretion removes metabolic waste.

Definition

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

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.

Memory hook

Kidney filters, nephron fine-tunes, urine carries waste.

Examples and method

Worked example

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

Method to apply

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

Diagram support

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

How CBSE asks it

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

Avoid common mistakes

Common confusion

Students think excretion is the same as egestion.

Common wrong answer

Excretion means removing undigested food. This is wrong because that is egestion; excretion removes metabolic waste.

Exam tip

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

Quick check

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

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

Answer writing and exam use

1-mark answer

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

2-mark answer

Excretion is the removal of metabolic wastes from the body, mainly through kidneys, lungs, skin, and liver. Rule: Blood is filtered, useful substances are reabsorbed, and wastes are passed out as urine. After drinking a lot of water, the body may produce more dilute urine to maintain balance.

3-mark answer

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. Rule: Blood is filtered, useful substances are reabsorbed, and wastes are passed out as urine. After a salty meal, the kidneys help remove extra salts and adjust water content so the body stays balanced. Draw a nephron, explain urine formation, or differentiate excretion and egestion. Excretion means removing undigested food. This is wrong because that is egestion; excretion removes metabolic waste.
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