Chapter 41 - Animal Nutrition
Chapter 41 Animal Nutrition
Overview: The Need to Feed
All animals eat other organisms—dead or alive, whole or by the piece (including
In general, animals fit into one of three dietary categories.
Herbivores, such as gorillas, cows, hares, and many snails, eat mainly autotrophs
(plants and algae).
Carnivores, such as sharks, hawks, spiders, and snakes, eat other animals.
Omnivores, such as cockroaches, bears, raccoons, and humans, consume animal and
plant or algal matter.
Humans evolved as hunters, scavengers, and gatherers.
While the terms herbivore, carnivore, and omnivore represent the kinds of food that an
animal usually eats, most animals are opportunistic, eating foods that are outside their
main dietary category when these foods are available.
For example, cattle and deer, which are herbivores, may occasionally eat small
animals or bird eggs.
Most carnivores obtain some nutrients from plant materials that remain in the
digestive tract of the prey that they eat.
All animals consume bacteria along with other types of food.
For any animal, a nutritionally adequate diet must satisfy three nutritional needs:
A balanced diet must provide fuel for cellular work.
It must supply the organic raw materials needed to construct organic molecules.
Essential nutrients that the animal cannot make from raw materials must be provided
in its food.
Concept 41.1 Homeostatic mechanisms manage an animal’s energy budget
The flow of food energy into and out of an animal can be viewed as a “budget,” with the
production of ATP accounting for the largest fraction by far of the energy budget of most
ATP powers basal or resting metabolism, as well as activity and, in endothermic
Nearly all ATP generation is based on the oxidation of organic fuel molecules—
carbohydrates, proteins, and fats—in cellular respiration.
The monomers of any of these substances can be used as fuel.
Fats are especially rich in energy, liberating about twice the energy liberated from an
equal amount of carbohydrate or protein during oxidation.