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2.12–2.14: Lipids store energy for a rainy day.

Lipids are macromolecules—made up primarily from carbon, hydrogen, and oxygen—that are insoluble in water. Lipids are important in energy storage, as hormones, and in membrane structure. The breakdown of dietary fats releases more energy per gram than other macromolecules.

Question 2.26

Which of the following statements about fiber is incorrect?

a) Dietary fiber reduces the risk of colon cancer.
b) Fiber in the diet slows the passage of food through the intestines.
c) Humans cannot extract energy from fiber.
d) The cellulose of celery stalks and lettuce leaves is fiber.
e) Fiber scrapes the wall of the digestive tract, stimulating mucus secretion and aiding in the digestion of other molecules.

Question 2.27

A dietary fatty acid is liquid at room temperature (i.e., it has a low melting point) and contains carbon-carbon double bonds. It is most likely from:

a) a plant
b) a cow
c) a pig
d) a chicken
e) a lamb

Question 2.28

In an unsaturated fatty acid:

a) carbon-carbon double bonds are present in the hydrocarbon chain.
b) the hydrocarbon chain has an odd number of carbons.
c) the hydrocarbon chain has an even number of carbons.
d) no carbon-carbon double bonds are present in the hydrocarbon chain.
e) not all carbons in the hydrocarbon chain are bonded to hydrogen.

Question 2.29

Which statement about phospholipids is incorrect?

a) They are used as organisms’ chief form of short-term energy.
b) They are hydrophobic at one end.
c) They are hydrophilic at one end.
d) They are a major constituent of cell membranes.
e) They contain glycerol linked to fatty acids.

Question 2.30

Proteins are an essential component of a healthy diet for humans (and other animals). Their most common purpose is to serve as:

a) raw material for growth.
b) fuel for running the body.
c) organic precursors for enzyme construction.
d) long-term energy storage.
e) inorganic precursors for enzyme construction.