Ch 7 Nutrition in humans Think about (Ch 7, p.2) 1. The stomach churns food into smaller pieces physically. The stomach wall secretes proteases to chemically digest proteins. It also releases hydrochloric acid which can kill most bacteria in food. The small intestine is the main site of nutrient absorption. 2. As food bypasses most of the stomach and the duodenum, it is not fully digested. Therefore, few nutrients are absorbed by the body. 3. This may lead to malnutrition since most of the consumed food is undigested and the body cannot obtain enough nutrients. Quick Practice (Ch 7, p.11) 1. B 2. D Enamel (1), dentine (2) and jaw bone (3) are calcified tissues. Bones are living tissues as they are capable for growth. The presence of nerve endings and blood vessels are also proofs of living tissue. Quick Practice (Ch 7, p.14) C is the answer. At point X, the circulatory muscles contract and the longitudinal muscles relax. The lumen becomes smaller and the food bolus is pushed forward. At point Y, the circulatory muscles relax and the longitudinal muscles contract. The lumen becomes larger to allow the food bolus to pass through. Quick Practice (Ch 7, p.25) 1. B 2. D In structure 1 (the mouth cavity), salivary amylase catalyses the breakdown of starch into maltose. In structure 3 (the small intestine), carbohydrases catalyse the breakdown of disaccharides (e.g. maltose and sucrose) into monosaccharides (e.g. glucose). Structure 6 is the bile duct. If the bile duct were blocked, bile produced by the liver could not be released into the duodenum. There would be no bile salts to emulsify fat. A is incorrect. Bile would still be secreted by the liver. B is incorrect. Bile contains no enzymes. Lipase is present in pancreatic juice secreted by the pancreas. 1
C is incorrect. Bile is alkaline. Without bile to neutralise the acidic food from the stomach, the ph of the food in the duodenum would decrease. Quick Practice (Ch 7, p.31) 1. D 2. B Vessel X is a blood capillary; vessel Y is a lacteal. The foldings on the surface of the epithelial cell increase the surface area for food absorption, hence the rate of absorption. Quick Practice (Ch 7, p.35) D is the answer. A is incorrect. Excess proteins are not stored in human bodies. Instead, they are broken down into amino acids which are then deaminated by the liver. B is incorrect. Urea is removed by the kidneys. C is incorrect. Blood glucose levels are detected by the cells in the pancreas. The pancreas regulates blood glucose levels through the action of two hormones, insulin and glucagon. The liver is one of the target organs (an effector) of insulin and glucagon. Quick Practice (Ch 7, p.37) A is the answer. Urea is excreted in urine. Section exercise (Ch 7, p.42) 1. (a) ingestion (b) digestion (c) absorption (d) assimilation (e) egestion 2 (a) oesophagus (b) liver (c) colon / large intestine (d) stomach (e) pancreas 2
(f) ileum / small intestine 3. E 4. B 5. D 6. A 7. C 8. (a) Incisor (b) Chisel-shaped (c) Biting and cutting (d) Pointed (e) 1 (f) Tearing food (g) Broad top with cusps (h) 1 or 2 (i) 2 or 3 (j) Crushing and grinding 9. The dental formula is a way of expressing the types and number of teeth on one side of the upper and lower jaws. 2 1 2 3 2123 10. i, c, pm, m (or ) 2 1 2 3 2123 11. Food is chewed by the teeth during mastication. The food is mixed with saliva and rolled into a bolus by the tongue. 12. Behind the bolus, circular muscles contract and longitudinal muscles relax. The lumen becomes smaller. The bolus is squeezed forward. In front of the bolus, circular muscles relax and longitudinal muscles contract. The lumen becomes larger to allow the bolus to pass through. 13. F 14. T 15. F 16. T 17. (a) Salivary gland (b) Salivary amylase (c) Maltose (d) Gastric gland 3
(e) Protease (f) Peptides (g) Pancreas (h) Pancreatic amylase (i) (j) Fatty acids and glycerol Proteases 18. F 19. T 20. F 21. F 22. C 23. B The large intestine is the last site for absorbing water from undigested materials. The undigested materials become faeces which are expelled from the body through the anus. After produced by the liver, bile is temporarily stored in the gall bladder. Revision exercise (Ch 7, p.44) 1. B 2. D 3. A 4. B 5. C Having three roots is a unique characteristic of a molar. Number of the type of teeth shown = (2 + 2) 2 = 8 Peristalsis occurs in the whole length of the digestive tract to squeeze food forward. Structure 4 is the bile duct which carries bile from the gall bladder to the duodenum. It does not carry out peristalsis. Cereal grains are rich in carbohydrates and proteins. Insect feeding on cereal grains should have amylase and protease to digest the carbohydrates and proteins present. Blood proteins are present in mammalian blood and the membranes of blood cells are composed of proteins and lipids. Insects feeding on mammalian blood should have protease and lipase to digest the nutrients. The main function of mucus is lubricating food to make it easier to swallow. 4
6. D Structure 1 is the stomach. It produces pepsin that digests proteins. Structure 2 is the pancreas. It produces pancreatic juice which contains proteases. Structure 3 is the small intestine. Proteases are present on the cell membranes of the epithelial cells in the wall of the small intestine. 7. D is the answer. Water and minerals are absorbed in structure 4 (colon). Removal of part of the colon reduces water and mineral absorption from the faeces. The faeces become watery. 8. C is the answer. The digestion of proteins is less effective as less pancreatic juice, which contains pancreatic proteases, reaches the small intestine to help digest proteins. 9. B 10. C 11. C 12. C 13. B 14. C A is incorrect. The blockage of the pancreatic duct has no effect on the secretion of glucagon. Glucagon is secreted into the bloodstream directly. B is incorrect. The pancreatic juice contains sodium hydrogencarbonate which makes it alkaline. If the pancreatic duct is blocked, pancreatic juice cannot reach the small intestine and the ph of the food decreases. D is incorrect. The absorption of digested food is not related to the pancreas. Amylase catalyses the hydrolysis of starch into glucose, which diffuses out of the dialysis tubing. Being a reducing sugar, glucose causes the formation of a brick-red precipitate in Benedict s test. Starch molecules are too large to diffuse out of the dialysis tubing. Thus, the iodine solution remains brown. The dialysis tubing represents the wall of the small intestine. Starch and amylase mixture in the tubing represent the mixture of undigested food and digestive enzymes in the small intestine. Water surrounding the tubing represents blood. The gastric bypass directs ingested food to the ileum without passing through the stomach and duodenum and hence, there should be a decrease in the digestion in the duodenum. Less food substances are available for absorption due to a decrease in digestion. Being fat-soluble, fatty acids can dissolve in the phospholipid bilayer of the cell membrane and enter the epithelial cells of the small intestine by simple diffusion. Vessel R (hepatic portal vein) carries blood from the villi of the small intestine to the liver. The blood glucose concentration fluctuates according to the amount of food absorbed by the small intestine and increases shortly after a meal. 5
15. B Digestive glands are glands that produce secretions to help in digestion. 16. (a) X: molar (1) Y: canine (1) Z: incisor (1) (b) Chewing physically breaks down food into smaller pieces. (1) This increases the surface area of food for enzyme action. (1) Food is also mixed with saliva (1) which contains amylase to catalyse the breakdown of starch (into maltose). (1) 17. HKCEE Biology 2003 Paper 1 Q2(c)(i) (ii) (Total: 7 marks) 18. HKDSEE Biology 2013 Paper 1 Section B Q3 19. (a) A (1) (b) The cell membrane of cell X is folded to form many microvilli. (1) This increases the surface area for food absorption. (1) Cell X contains a large number of mitochondria. (1) which provide energy for the active uptake of digested food substances. (1) (c) The cell membrane is composed of a phospholipid bilayer. (1) Being non-polar, the digested products of fat (fatty acids and glycerol) can dissolve in the phospholipid bilayer and diffuse through the cell membrane. (1) 20. HKCEE Biology 2006 Paper 1 Q2 (Total: 7 marks) 21. (a) (i) Proteins are digested / broken down into amino acids (1) by the action of proteases in the stomach and small intestine. (1) The amino acids are then absorbed into blood capillaries of the villi (1) and carried to the liver through blood vessel Z. (1) (ii) The liver deaminates excess amino acids by removing and converting the amino groups into urea. (1) (b) (i) Gall bladder (1) (ii) Emulsifies fat into small droplets / neutralises the acidic chime and provides an alkaline medium needed for the enzymes in the duodenum (1) (Total: 7 marks) 22. HKCEE Biology 2008 Paper 1 Q1 6
23. HKCEE Human Biology 2004 Paper 1 Q1(c) 24. (a) X is a finger-like projection of the intestinal wall. (1) This feature provides a large surface area for food absorption. (1) The epithelium of X is very thin / one-cell thick. (1) This shortens the distance of diffusion / transport of digested food substances. (1) (b) X hepatic portal vein liver hepatic vein vena cava (heart) (0.5) 4 (c) (i) Muscle layer A. (1) Muscle cells appears as thread-like / fibres in the cross section. (1) (ii) The alternative contraction of these two layers of muscles result in peristalsis. (1) Any two of the following: (2) Peristalsis moves the food along the intestine. (1) Peristalsis mixes the food with digestive juices. (1) Peristalsis increases the contact between villi and digested food to facilitate absorption. (1) (Total: 11 marks) 25. (a) (i) Cabbage mainly consists of carbohydrate / cellulose. (1) Gastric juice does not contain carbohydrase / cellulase / enzymes that can digest carbohydrate or cellulose. (1) (ii) (1) Food sample (1) (2) Time to complete digestion (1) (3) Any one of the following: (1) constant temperature (1) same size of food substance used in experiments (1) (b) (i) Experiments 3 and 4 (1) (ii) The digestion of beef is more effective at 37 C than at 20 C. (1) Gastric juice contains proteases. (1) The enzyme works better at 37 C which is close to its optimal temperature. (1) (c) Digestion in stomach is faster because of mechanical digestion / physical digestion. (1) Stomach also provides constant supply of acids or enzymes. (1) 26. HKDSEE Biology 2012 Paper 1 Section B Q10 (Total: 11 marks) 27. HKCEE Biology 2011 Paper 1 Q9(b) 7
28. Digestion of food in the mouth cavity Food is chewed into small pieces by the teeth in the mouth cavity. (1) This increases the surface are of food in contact with the saliva (1) which contains amylase to catalyse the breakdown of starch into maltose. (1) Digestion of food in the stomach In the stomach, food is churned and mixed with the gastric juice. (1) Gastric juice contains protease which catalyses the breakdown of proteins into peptides. (1) Digestion of food in the small intestine In the duodenum receives the bile and pancreatic juice for digestion. The bile contains bile salts which emulsify lipids into small droplets, (1) thereby increasing the surface are for the action of lipase. (1) Pancreatic juice secreted by the pancreas contains lipase which catalyses the breakdown of lipids into fatty acids and glycerol. (1) Pancreatic amylase catalyses the breakdown of starch into maltose. (1) Pancreatic juice also contains proteases which catalyse the breakdown of proteins into peptides and amino acids. (1) The wall of the small intestine has specialised cells that have various enzymes on their cell membranes. Carbohydrases catalyse the breakdown of disaccharides (e.g. maltose and sucrose) into monosccharides (e.g. glucose). (1) Proteases catalyse the breakdown of peptides into amino acids. (1) (Total: 12 marks) 29. Effects on carbohydrate metabolism (max. 3) Less glucose is absorbed by the liver (1) Less glycogen is stored in the liver (1) (because) cells do not respond to insulin (1) Less release of glucose from stored glycogen (1) (if) cells do not respond to glucagon (1) Less production of glucose from amino acids / glycerol (1) Effects on protein metabolism (max. 3) Less breakdown of protein (1) Less conversion of amino acids to ammonia / less deamination (1) Less production of urea (1) Reduced synthesis of protein (1) 8
Consequences of any of the above (max. 2) blood clotting (1) transport role of proteins (1) water potential (1) blood glucose concentrations remain high / inability to regulate blood glucose / diabetic (1) need for amino acid supplements (1) Communication (max. 3) (Total: 11 marks) Article reading (Ch 7, p.51) 1. One of the proteases secreted by the stomach catalyses the breakdown of proteins into peptides. (1) The acid provides an acidic medium needed for the action of proteases. (1) 2. The stomach wall secretes mucus (1) which forms a protective layer that covers the inner surface of the stomach. (1) 3. Because they thought that bacteria were killed by the acid secreted by the stomach and could not survive in the stomach. (1) 4. Introduce H.pylori into the stomach of healthy mammals. (1) If the hypothesis is correct, these mammals would develop symptoms of gastric ulcer. (1) 9