Page 114 - Science Class 07

produce large volumes of dilute urine and take Excre on in Birds
in salts from the water through specialised cells Birds excrete uric acid into a con nua on of
in their gills. Nitrogenous wastes, for the most the alimentary canal. Some marine birds have,
part, are diffused as ammonia through the skin. in addi on, salt glands (modified), tear glands
Marine fish, on the other hand, lose water which remove excess salt from their bodies and

through the skin and take in salt by osmosis. discharge concentrated solu on through the
nostrils.

1. How excre on takes place in unicellular organisms?

2. Name the excretory organs of insects.

3. How nitrogenous substances are excreted from the body of fish?

Excretion : A process of releasing wastes out of the body
Metabolism : The process of digestion of food and releasing energy inside the body
Egestion : Expulsion of faecal wastes out of body

Exhalation : Releasing gaseous wastes out of body
Dialysis : Artificial method to remove toxic wastes from the body of the patient
suffering from kidney failure
Transplant : Replacing a damaged organ with a healthy organ

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i The food we eat, the water we drink and the air we breathe produce wastes in the form of
solid, liquid and gaseous wastes respectively.
i Solid wastes come out of the body in the form of faecal wastes, liquid wastes come out of
the body in the form of sweat and urine and gaseous wastes come out of the body in the
form of carbon dioxide.

i Kidneys are paired bean-shaped organs about 10 cm long.
i Human excretory or urinary system consists of two kidneys ureters, urinary bladder and
urethra.

i Each kidney consists of about one million functional units called nephrons.
i Kidneys remove waste products present in blood.

i Frequent discharge of urine indicates that the man may be suffering from diabetes.
i Dialysis is a method given to the patient who is suffering from kidney damage. With the
help of this artificial method, toxic wastes are removed from the body of the patient.

i In earthworms, nephridia constitute the excretory organ.

114 Science-7