(a) Nutrition is necessary for the human body because it provides essential nutrients required for:
- Energy production
- Growth and repair of body tissues
- Proper functioning of organs and maintenance of body processes
(b) The movement of food is caused by peristalsis — a wave-like muscular contraction and relaxation of the walls of the alimentary canal that pushes the food forward.
(c) Herbivores eat plant-based food, which is rich in cellulose and is harder to digest. They need a longer small intestine to allow more time for digestion and absorption. Whereas, Carnivores eat meat, which is easier to digest, so they have a shorter intestine.
(d) If mucus is not secreted, the hydrochloric acid (HCl) in the stomach will corrode the stomach lining, causing ulcers or damage to the tissues.
