22.1–22.3 Food provides the raw materials for growth and the fuel to make it happen.

Animals must eat for two reasons: to acquire the energy needed for all growth and activity, and to acquire the raw materials required for life.

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Question 22.25

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

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

Question 22.26

Various types of vitamin and mineral supplements are generally necessary for individuals in all of the following categories except:

  • a) post-menopausal women.
  • b) healthy people with good diets.
  • c) people on extremely low-calorie diets.
  • d) pregnant women.
  • e) people with limited milk consumption or sun exposure.

Question 22.27

Why do birds eat gravel?

  • a) Gravel contains most of the essential minerals for a bird’s diet.
  • b) Birds have poor vision and have difficulty distinguishing gravel from small seeds.
  • c) By chewing on gravel, birds are able to sharpen their teeth, increasing their ability to crack open hard nuts or catch their prey.
  • d) The gravel collects in the gizzard (one of the two chambers of the bird stomach), where it helps to grind up the food they eat.
  • e) Because they have such a small brain relative to body size, birds tend to be the least intelligent of the vertebrates.

Question 22.28

Cross-culturally, humans have developed ways of preparing food, including using heat and marinating food in acidic solutions, such as lemon juice. How might these be adaptations that help with digestion?

  • a) Heat and acid help disrupt the tissue of food items. This causes digestive enzymes to have increased contact with the food molecules and break them down.
  • b) By reducing the need for chyme, these methods of food preparation increase the caloric value of food.
  • c) Because even the weakest acids are toxic to all bacteria, these methods of food preparation reduce the incidence of dietary-induced bacterial infection.
  • d) These methods increase the body’s ability to extract energy from normally indigestible cellulose.
  • e) These food preparation methods reduce the need for water consumption.