Nutrition involves the intake and processing of food by living things. There are two main types of nutrition: autotrophic and heterotrophic. Autotrophs like plants can produce their own food, while heterotrophs like animals must consume other organisms for nutrients. The document goes on to describe the key processes of nutrition - obtaining nutrients, respiration, distribution of substances in the body, and excretion of waste products. It also explains the digestive and circulatory systems that facilitate these processes in animals and plants.