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Lungs, skin, liver have their own specific functions but carry out
excretion as a secondary function.
Lungs: In respiratory process lungs remove carbon
dioxide and water.
Skin: It consists of large number of sweat glands
richly supplied with blood capillaries, from which
fig-10: Lung, Skin they extract sweat and some metabolic wastes.
84 X Class Excretion The wastage disposing system
Since the skin sends out plenty of water and small amount of salts, it serves
as an excretory organ. Sebaceous glands in skin eliminate sebum which
contains waxes, sterols, hydrocarbons and fatty acids.
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Collect information on sebum and prepare a news bulletin, display
it on bulletin board?
People in cold countries get very less/no sweat. What changes oc-
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cur in their skin and in other excretory organs?
Liver: It produces bile pigments (bilirubin ,biliverdin and urochrome)
which are metabolic wastes of haemoglobin of dead R.B.Cs. The life span
of RBC is 120 days. They are destroyed in the liver. Urochrome is
eliminated through urine. Biliverdin and bilirubin are excreted through
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bile along with cholesterol and derivatives of steroid hormones, extra drug,
vitamins and alkaline salts. Liver is also involved in urea formation.
Large intestine: Excess salts of calcium magnesium and iron are excreted
by epithelial cells of colon (large intestine) for elimination along with the
faeces.
Small amount of nitrogenous wastes are also eliminated through saliva fig-11: Liver,
and tears.
LA intestine
Excretion in other organisms
Different organisms use varied strategies in excretion. Specific
excretory organs are absent in unicellular organisms. These organisms
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remove waste products by simple diffusion from the body surface into the
surrounding water. Fresh water organisms like Amoeba, Paramoecium
possess osmoregulatory organelle called contractile vacuole. It collects
water and waste from the body, swells up, reaches the surface and bursts
to release its content to outside. The main excretion takes place through
body surface (Diffusion).
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Table-4
Name of the phylum/ Excretory system/
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organism organ
Protozoa Simple diffusion from the body surface in to
the surrounding water
Porifera and coelenterates Water bathes almost all their cells
Platyhelminthes Flame cells
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Nematoda Renette cells
Annelids Nephridia
Arthropoda Green glands, Malpighian tubules
Mollusca Meta nephridia
Echinodermata Water vascular system
Reptiles, Aves and Mammals Kidneys
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Free distribution by T.S. Government 2019-20 85
Multicellular organisms possess different excretory organs for
removal of waste materials from the body. Structural and functional
complexity of excretory organs increases from sponges to humans.
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Sponges and coelenterates do not have specific excretory organs as water
bathes almost all their cells. Excretory structures appear for the first time
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in Flatworms (Platyhelminthes) are known as flame cells.
Now let us see how this vital process takes place in plants
Excretion and release of substance in plants