2. These are organic macromolecules e.g. Carbohydrates, fats and proteins.
Protective principles of food :
1. These do not provide energy.
2. These are micromolecules both organic and inorganic molecules just as vitamins, minerals and water.
2. The digestion may be intracellular or extracellular.
Saprozoic Nutrition :
1. In this mode of nutrition the organism feeds on dead and decaying matter.
2. It is generally extracellular and absorbs diffusible food.
Gall stones : Gallstones formed in gall bladder may consist of cholesterol, salt, or bilirubin, which is discarded red blood cells. Gallstones range in size and can be as small as a grain of sand or as large as an apricot. Some gall stones contain large amounts of calcium.
Peristalsis is the travelling wave of alternate contraction and relaxation which pass from anterior end of alimentary up to posterior end of alimantary.
Peristalsis is produced by involuntary contraction of circular muscles which is preceded by a simultaneous contraction of longitudinal muscles and relaxation of circular muscles present in gut wall.
These waves of contraction and relaxation help in properly mixing up of food with digestive enzymes for proper digestion and the movement of the food thhroguh the alimentary canal.