Theory question 102
Animal Nutrition(a) Define the following terms: (i) elimination; (ii) excretion; (iii) secretion.
(b) Describe the digestion of boiled fish in the gut of humans.
(c) Make a diagram 8 cm – 10 cm long of a longitudinal section of a villus and label fully.
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(a)(i) Elimination (egestion): removal of undigested food (faeces) from the alimentary canal through the anus.
(ii) Excretion: removal of waste products of metabolism (e.g. urea, CO2) from the body.
(iii) Secretion: release of useful substances (e.g. enzymes, hormones, mucus) made by cells or glands.
(b) Fish is mainly protein (and some fat). Mouth: chewed and moistened with saliva (no protein digestion). Stomach: HCl kills germs and gives acid pH; pepsin breaks proteins into polypeptides/peptones. Duodenum: bile emulsifies fats; pancreatic trypsin breaks proteins/polypeptides into peptides; lipase breaks fats into fatty acids and glycerol. Ileum: erepsin (peptidase) breaks peptides into amino acids; intestinal lipase completes fat digestion. Amino acids are absorbed into blood capillaries of the villi; fatty acids and glycerol into the lacteals.
(c) Diagram of correct size with title, labels: epithelium (single layer of cells); microvilli; blood capillaries; arteriole and venule; lacteal (lymph vessel); goblet cells; connective tissue.
Follow the protein from mouth to ileum, naming the enzyme and product at each stage.