(a) Describe briefly the role of the stomach in digestion.
(b) (i) Name three parts of plants in which food can be stored.
(ii) Give one example in each case.
(c) Explain briefly how the level of sugar in the mammalian blood can be regulated.
Explanation
(a) Role of the stomach in digestion: The stomach receives food when the sphincter at the entrance of the stomach relaxes. The muscular walls of the stomach contract and relax, to churn/mix the food, and further break down the particles. The stomach produces gastric juices, which contain dilute hydrochloric acid/pepsin/rennin. The dilute hydrochloric acid neutralizes the action of the salivary amylase, and kills bacteria present in the food. It creates a suitable condition/pH for the action of pepsin, and activates inactive pepsinogen to form pepsin. The pepsin breaks down the protein to polypeptide/peptides. While the rennin coagulates/curdles milk to enhance digestion by pepsin. The mucus produced by the stomach wall lines the wall of the stomach to prevent the action of the acid on the stomach wall. The mucus produced by the stomach lubricates the movement of the food in the alimentary canal.
(b)(i) Parts of plants where food is stored: Leaves. Stems. Roots. Seed. Fruits.
(ii) Examples:
Leaves: Onions, shallot, garlic.
Stems: Yam, sugarcane, ginger, Irish potatoes.
Roots: Cassava, carrots, sweet potatoes.
Seed: Groundnut, beans, coconut, cashew.
Fruits: Maize, guava, orange, pawpaw, cashew, palm nut, mango.
(c) Sugar regulation in mammals: The liver controls the blood glucose levels. It converts excess glucose in the blood to glycogen. The process is stimulated by the hormone insulin, which is secreted by the pancreas. When the blood glucose level falls below normal. The pancreas secretes/glucagons. This stimulates the conversion of glycogen into glucose, which is released into the blood.