Grade 7, Science Olympiad (CBSE) - Excreation 

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Grade 7  |   Science  |   Excreation, Transportation in animals and plants, Olympiad, CBSE, ICSE, Maths Olympiad, Science Olympiad, English Olympiad


There are so many activities which keep on going inside the body of living beings and such activities are collectively called metabolism. Many toxic substances are formed as a by-product during metabolic reaction inside our body. The accumulation of such toxins inside the body will be fatal until not removed from the body in time. This process of removal of waste material from the body is called excretion.

The human excretory system is composed of a pair of kidney, ureter and urinary bladder.


They are bean-shaped organs present in the abdomen on the back side of the body. They act as filters. Blood, laden with water enters the kidney where the waste is filtered from the blood and the purified blood is sent back in the circulatory system.

The wastewater from the kidneys travels from ureters to reach the urinary bladder where it is excreted out of the body from time to time. This waste water is what we call Urine. It contains 95% water, 2.5% urea, and 2.5% other wastes. 

The animal body produces nitrogenous waste as the main waste which is to be excreted out of the system. Different types of animals produce different types of  nitrogenous wastes like- Ammonia, Urea and Uric acid. On the basis of this animals has been categorized in three types.


Here, ammonia is the main nitrogenous waste in animals like fish, frog etc. A lot of water is required to remove such wastes from the body. 


Here, urea is the main nitrogenous waste in animals like mammals. Such animals require less water for removal of waste. 


Here, Uric acid is produced as the main nitrogenous waste in animals like reptiles and aves. 

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