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SAI International School
Std -X, Subject- BIOLOGY
Chapter- Life Processes
Sub Topic- Excretion in Human beings
Module- 11
Lesson notes

 Excretion is a biological process by which an organism gets rid of or toxic waste
products of metabolism.
 Excretion removes unwanted by-products of metabolism, toxic chemical
substances, regulate the ionic concentration of body fluids, regulates water content
of body, regulate pH of body fluids.
 Different organisms follow different modes of excretion. In complex organisms
including humans, there is a specialized system for excretion called human
excretory system.
 We all obtain our nutrients from different sources which are later digested and
metabolized in our body. After metabolic reactions, the body starts to sort out useful
and toxic substances in an individual.
 As we all know, the accumulation of the toxins may be harmful and the body
removes all the metabolic wastes by the process called excretion.
 Different organisms follow different modes of excretion such as kidney, lungs, skin
and eyes depending on their habitat and food habit.
 For example- i. Many unicellular organisms remove these wastes by simple
diffusion from the body surface into the surrounding water.
ii. Aquatic animals excrete waste in the form of ammonia, while birds and insects
excrete mainly uric acid. Humans produce urea as the major excretory product.

Excretory System Organs

The diagram below represents the different parts of the human excretory system.

The human excretory system organs include: