Nutrition, Feeding, Digestion
All organisms require a fairly steady supply of nutrient materials from the environment to obtain energy in order to stay alive. The animals are heterotrophs because they depend on already synthesised organic compounds from plants and other animals to obtain their food. Unlike autotrophs (plants and chemosynthetic bacteria) animals have only limited synthesising abilities.
The cellular metabolism provides energy for various processes in organisms, like locomotion, excretion, osmoregulation, synthesis of new materials for growth and maintenance and reproduction. To provide energy for these processes raw material or nutrients are required which are supplied by food. In addition animals require amino acids, vitamins and minerals which they cannot synthesise. The study of nutrition involves both the need for food to provide energy and the need for specific food components. The process by which animals acquire and ingest their food is referred to as feeding.
Diverse types of feeding mechanisms have been evolved by different groups of animals. Virtually all food whether of plant or of animal origin has to be broken down to simple compounds by the process of digestion. Digestion and absorption of food constitute the essential link between nutrition and metabolism. In this unit we shall first discuss the nature and components of food and the specialised feeding mechanisms. There exists a relationship between the nature of ingested food and type of feeding mechanism used in acquiring the food. Then we will consider the digestion and absorption of nutrients. Towards the end of the unit we shall be discussing the energy metabolism in animals.