The processes which together perform the function of maintenance of 'life' are called as life processes. Nutrition, respiration, circulation, excretion are examples of essential life processes. In unicellular organisms, all these processes are carried out by that single cell. There are six life processes that all living organisms perform. They are movement, respiration, growth, reproduction, excretion and nutrition. The various modes of nutrition are discussed in detail, such as autotrophic and heterotrophic nutrition. A brief idea about the human digestion process right from the ingestion of food, food passage through the alimentary canal, food absorption, until the stage when digested food is ready to be excreted is explained. Students are also enlightened with the process of respiration (which can either be aerobic or anaerobic) from inhalation to the breakdown of organic compounds due to the supply of energy in the form of ATP. In humans, the process of transportation of substances such as food, carbon dioxide, oxygen, and other materials is carried out by the circulatory system, which is explained. The various constituents of the circulatory system, such as blood, blood vessels, and the heart, are also briefed.
The diverse functions of the excretory organs and its structure, in abstract, are shed light upon in this chapter. It also covers excretion in plants, and the techniques plants use for excretion of waste products.