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Answers to Thinking Critically Questions
Mader: Inquiry into Life, Twelfth Edition
Chapter 14
1. Suppose that, starting today, your body would lose the ability to perform mechanical
digestion or chemical digestion. Which type would your choose to keep and why?
Explanation/Answer: It is unlikely that a person could survive on mechanical
digestion alone, since it would be very difficult to break foods down into small
molecules through physical action only. In contrast, chemical digestion alone, though
inefficient, would probably be able to provide some useable small nutrients.
2. Trace all of the types and locations of enzymes that might be involved digesting a
molecule of a complex carbohydrate such as starch, all the way through the utilization
of a glucose molecule by a body cell.
Explanation/Answer: Salivary amylase in the saliva. Pancreatic amylase in the
small intestine. Maltase in the small intestine. Various enzymes in the cell involved
in glycolysis (see Chapter 6).
3. Suppose that, as you are swallowing a small piece of apple, your epiglottis
malfunctions, and the apple “goes down the wrong pipe.” If the piece is small
enough to make it into one or your bronchial tubes, but doesn’t obstruct your airway
in any significant way, how long do you think it could stay there?
Explanation/Answer: Theoretically it could stay there a long time, unless enough
salivary amylase was present to digest it so it could be absorbed, however slowly, buy
the respiratory tract. More likely, bacteria would find the partially digested apple a
good source of food, and would begin to cause problems with infection. That is one
(of several) of the reasons why you would probably want to see a physician about
getting that chunk of food removed.
4. Pancreatic cancer is one of the most lethal cancers, with a survival rate of only about
5%. Why is the pancreas such a vital organ?
Explanation/Answer: It produces insulin and glucagon, which regulate blood
glucose levels. Glucose is an essential nutrient for most or all cells of the body.
5. Suppose you are taking large doses of creatine, an amino acid supplement that is
advertised for its ability to enhance muscle growth. Since your muscles can only
grow at a certain rate, what do you suppose happens to all the creatine that is not used
for synthesis of new muscle?
Explanation/Answer: As stated in the chapter, amino acids are not commonly used
as an energy source. However, consuming an excess of creatine, or a very high-
protein diet, would result in the excess amino acids either having to be secreted by the
urinary system as nitrogenous waste, or being used as an energy source (and
potentially converted into fat!).