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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