Living things feed. Food is the material from which organisms through respiration obtain the energy required to sustain life and carry out all the other defining functions of living things. Food also provides the raw materials for growth and repair. The study of food and feeding is called nutrition.
There are two types of nutrition:
|Autotrophic nutrition||Autotrophic organisms make their own food by a process called photosynthesis. Green plants, for example, manufacture sugar and starch from carbon dioxide and water using the energy of sunlight to drive the necessary chemical reactions.|
|Heterotrophic nutrition|| Heterotrophic organisms obtain their food from
the bodies of other organisms. This is done in various ways.
Herbivores such as cattle, tortoises and sparrows eat plants.
Carnivores such as lions, crocodiles, sharks and kestrels eat the flesh of other animals.
Omnivores such as humans can eat both plants and animals.
Saprophytes such as many types of fungi and bacteria, obtain their food in liquid form from the remains of dead organisms. This feeding manifests itself as the process called decay.
Parasites such as tapeworms and mosquitoes live on or in another living organism (called the host) from which they obtain food.