key concept 50.1 Food Provides Energy As Well As Materials for Biosynthesis

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Animals are heterotrophs—they derive their nutrition from eating other organisms. In contrast, autotrophs (most plants, some bacteria, some archaea, and some protists) can use solar energy or inorganic chemical energy to synthesize all of their components. Of course, some *plants are also heterotrophs.

*connect the concepts Carnivorous and parasitic plants are discussed in Key Concept 35.5.

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  • Fats, carbohydrates, and proteins in food provide energy.

  • Energy is stored in animal bodies as glycogen and fat.

  • Some small organic molecules required for biosynthesis, including essential amino acids and fatty acids, must come from food.

  • Vitamins are organic compounds that the animal cannot synthesize but are required for healthy cell function.

  • Animals require a variety of mineral nutrients.

Directly and indirectly, heterotrophs take advantage of—indeed, depend on—the organic synthesis carried out by autotrophs and have evolved an enormous diversity of adaptations to exploit this resource (Figure 50.1). In this section we describe how animals use food, be it plants or other animals, to obtain energy and building blocks of complex molecules. We also consider the need for special mineral nutrients and organic molecules and the diseases that result when they are lacking in the diet.

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Figure 50.1 Heterotrophs Get Energy from Autotrophs (A) Herbivores get their energy directly from autotrophs. The large herbivores of the African grasslands must consume huge amounts of plant matter to fulfill their nutritional needs. (B) A carnivore’s energy is indirectly obtained from autotrophs, since the energy stored in a prey animal was originally obtained from autotrophs.