Theory question 102
Animal Nutrition(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.
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(a) Stores food for a few hours; muscular walls contract to churn and mix food with gastric juice; gastric glands secrete hydrochloric acid, pepsinogen, rennin and mucus; HCl kills germs, stops salivary amylase and gives an acid pH; HCl activates pepsinogen to pepsin, which breaks proteins into polypeptides/peptides; rennin curdles milk protein (caseinogen) in young mammals; mucus protects the stomach wall from acid and enzymes; food leaves as chyme through the pyloric sphincter.
(b) Any three, each with an example: root — cassava/carrot/sweet potato; stem — yam/ginger/sugar cane/Irish potato; leaf — onion/cabbage; fruit — mango/orange; seed — maize/groundnut/beans.
(c) When blood sugar rises (after a meal), the pancreas secretes insulin, which makes the liver and muscles change glucose into glycogen and cells take up more glucose, so the level falls. When blood sugar falls, the pancreas secretes glucagon, which makes the liver change glycogen back into glucose, so the level rises. (Adrenaline also raises blood sugar in emergencies.)
For (c) name both hormones and say what each makes the liver do.