EXCRETION – REVISION NOTES
1. What is Excretion?
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Excretion is the process of removal of metabolic waste products from the body.
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Wastes are produced during life processes.
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Accumulation of wastes is harmful to the organism.
2. Why is Excretion Necessary?
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Metabolic activities produce:
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Nitrogenous wastes
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Excess water
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Excess salts
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These wastes can be toxic.
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Excretion maintains:
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Internal balance
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Proper functioning of cells
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3. Excretion in Unicellular Organisms
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Occurs by diffusion.
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Waste products move from higher to lower concentration.
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Example: Amoeba.
4. Excretion in Human Beings
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Carried out by the excretory system.
Organs of Excretory System
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Kidneys
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Ureters
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Urinary bladder
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Urethra
5. Kidney
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Main excretory organ.
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Bean-shaped organs.
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One kidney on each side of backbone.
Functions
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Filters blood
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Removes nitrogenous wastes
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Maintains water and salt balance
6. Nephron
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Structural and functional unit of kidney.
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Each kidney has millions of nephrons.
Parts of Nephron
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Bowman’s capsule
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Glomerulus
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Renal tubule
7. Formation of Urine
Urine formation occurs in three steps:
1. Filtration
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Blood filtered in glomerulus.
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Water, urea, salts, glucose pass into Bowman’s capsule.
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Proteins and blood cells remain in blood.
2. Reabsorption
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Useful substances like:
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Glucose
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Amino acids
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Required salts
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Most water
are reabsorbed into blood.
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3. Secretion
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Excess salts and wastes are secreted into tubule.
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Helps maintain ionic balance.
8. Urine
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Yellowish liquid waste.
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Contains:
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Urea
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Excess salts
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Excess water
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Stored temporarily in urinary bladder.
9. Regulation of Water Balance
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Kidneys regulate amount of water excreted.
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More water intake → dilute urine
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Less water intake → concentrated urine
10. Excretion in Plants
Plants do not have specialised excretory organs.
Methods
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Gaseous wastes removed by diffusion.
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Excess water removed by transpiration.
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Wastes stored in:
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Leaves
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Bark
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Fruits
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Wastes removed when plant parts fall off.
11. Excretory Products in Plants
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Oxygen (from photosynthesis)
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Carbon dioxide (from respiration)
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Resins, gums, latex
12. Artificial Kidney (Dialysis)
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Used when kidneys fail.
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Blood is filtered through artificial membrane.
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Removes wastes from blood.
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Saves life of patient.
13. Key Differences
Excretion in Humans vs Plants
| Humans | Plants |
|---|---|
| Special organs present | No special organs |
| Kidneys remove waste | Diffusion & storage |
| Urine formation | Transpiration |
14. Key Exam Points
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Excretion removes toxic wastes.
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Kidney is main excretory organ.
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Nephron is functional unit of kidney.
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Urine formation involves filtration, reabsorption and secretion.
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Transpiration helps in excretion in plants.
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Dialysis used in kidney failure.