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2. (a) The inside surface of the small intestine is folded, forming tiny projections called villi. Each of the villi has even smaller, microscopic projections called microvilli. This folding and the villi and microvilli increase the surface area through which nutrients can be absorbed. (b) The folding of the middle layer of the corrugated cardboard in the Mini Investigation is similar to the folding of the inner surface of the small intestine. The surface area is increased in both cases. 3. When fat enters the duodenum, the gall bladder contracts and squeezes bile through the bile duct into the duodenum. Bile breaks down fats into tiny droplets called micelles, which are then acted on by enzymes called lipases, which digest lipids. 4. (a) The gall bladder is a pouch that stores the bile produced by the liver until it is needed for digestion. (b) Since the gall bladder contains a store of bile, the digestive system would have to depend on the secretions of bile directly from the liver to digest fats. If the gall bladder is removed, the reservoir of bile is not available, but bile will drip continuously into the duodenum. Without the reservoir, there may be insufficient bile and the digestive system may not be as effective at emulsifying the lipids in order for them to be digested. So, some lipids may pass through the digestive system undigested. (c) Answers will vary. Sample answer: Most sources suggest a low-fat diet following gall bladder removal. Other suggestions include lots of fluids and high-fibre foods. It is also recommended that low-fat dairy products be eaten rather than higher fat ones, and fast foods should be avoided because of their high fat content. 5. Answers will vary. Sample answer: Carbohydrates Lipids Proteins Food is broken down Food is broken down Food is broken down Physical into smaller pieces in the into smaller pieces in the into smaller pieces in the digestion mouth by chewing. The mouth by chewing. The mouth by chewing. The churning action of the churning action of the churning action of the stomach also breaks food stomach also breaks food stomach also breaks food into smaller particles. into smaller particles. into smaller particles. This breaks the food into Lipids are emulsified by This breaks the food into small pieces to increase the bile which is small pieces to increase the surface area for produced by the liver, the surface area for chemical digestion. stored in the gall chemical digestion. bladder, and released into the duodenum. This physical breakdown of lipids increases the surface area for the chemical breakdown of lipids. Starch digestion begins Enzymes called lipases The digestion of protein Chemical in the mouth when then continue the starts in the stomach by digestion amylase, an enzyme in breakdown of lipids. the enzyme pepsin. This saliva, breaks down continues in the small starch into sugars. This intestine with the process continues in the enzymes trypsin, small intestine carboxypeptidase, and erepsin. Copyright © 2011 Nelson Education Ltd. Chapter 9: Nutrition and the Digestive System 9.5-2 6. Answers will vary. Hormones are cholecystokinin and secretin. Cholecystokinin stimulates the pancreas to release digestive enzymes, and secretin is released in the duodenum to stimulate pancreatic secretions and the release of bile. Enzymes should include two of the following: amylase, which breaks down starches into sugars; lipase, which breaks down lipids into shorter chains and individual fatty acid molecules; pepsin, which breaks down proteins in the stomach, and trypsin, carboxypeptidase, erepsin, all of which break down proteins in the small intestine. 7. (a) The digestion of proteins starts in the stomach when the enzyme pepsin is released in the gastric juice. Pepsin requires an acidic environment in which to work. When chyme moves into the small intestine, other enzymes that do not require an acid environment continue the breakdown of proteins. The pancreas releases trypsinogen which is converted into trypsin by another enzyme called enterokinase. Trypsin and other protein-digesting enzymes, such as carboxypeptidase and erepsin, continue the breakdown of proteins into individual amino acids, which are absorbed into the bloodstream from the small intestine. (b) The body produces many proteins that are required for growth, maintenance, and regulation of body processes. The building blocks for proteins are amino acids. In order to build new proteins, the body requires a supply of the individual building blocks. These building blocks come from the proteins that are found in foods which are broken down during the process of digestion. 8. In simple diffusion and osmosis, substances move across a semi-permeable membrane by passing through the spaces in the membrane itself. In facilitated diffusion, the substances pass through the membrane with the help of a transport protein which is embedded in the membrane. 9. Students’ diagrams should be similar to the following: 10. (a) The colorectal screening program was implemented because of the high incidence of colorectal cancer in Ontario and in Canada. Its goals are to save lives by screening more at-risk people. This screening will hopefully lead to earlier diagnosis of the problem and a reduction in the number of deaths resulting from colorectal cancer. (b) The criteria used to identify those who should have a colonoscopy are anyone between 50 and 74 years of age that has had a positive test for blood in their feces, or anyone that has a family history of colorectal cancer. (c) Answers will vary. Student answers should show that they have identified the risks, benefits, and costs of a colonoscopy examination and have used this information to make a decision about the technology. Students may conclude, for example, that the risks are acceptable and the costs justified if the procedure prevents even a small number of deaths from colorectal cancer. Students may provide statistics showing that such screening programs are effective in reducing the number of deaths from colorectal cancer or other diseases of the digestive system. Copyright © 2011 Nelson Education Ltd. Chapter 9: Nutrition and the Digestive System 9.5-3