CHAPTER 40 INTRODUCTION

CORE CONCEPTS

40.1 Metabolic rate depends on level of activity, body size, and body temperature.

40.2 An animal’s diet supplies the energy it needs for homeostasis and essential nutrients it cannot synthesize on its own.

40.3 Different animals have different adaptations for feeding.

40.4 The digestive tract is a tubelike structure with regions specialized for different functions.

It is literally true that “you are what you eat.” Not only do animals build their bodies and obtain energy from the food they eat, but also their very appearance often reflects what they eat. Consider a cat. We know it’s a carnivore—an animal that eats other animals—just from looking at it. It has sharp teeth and powerful jaws specialized for tearing meat; strong legs, sharp claws, and keen eyesight for hunting prey; and a short gut because breaking down animal protein is easier than breaking down plant material. Humans are omnivores, adapted for eating both other animals and plants, and this is reflected in our anatomy. Our teeth include sharp canines for tearing meat and flat molars for grinding plant material. Finally, consider herbivores, such as cows, that eat plants. Cows have evolved a variety of adaptations, including a four-chambered stomach, that allow them to digest cellulose, which is tough but rich in energy.

Animals are heterotrophs, obtaining food from other organisms (Chapter 6). The energy animals obtain from food is essential for building bodies, moving, surviving, and reproducing. Much of an animal’s activity therefore centers on obtaining food. In turn, the biology of an animal is in large part shaped by the type of food the animal consumes. Furthermore, an animal’s metabolism, the chemical reactions by which it breaks down its food, is closely linked to the energy and nutrients contained in that food.

The food that an animal eats also affects its place in an ecosystem. Primary producers, such as plants and some algae, are food for a great diversity of animals. Animals that feed on plants tend to exist in large numbers. Large animals that feed on other, smaller animals exist in smaller numbers and commonly represent fewer species.

This chapter looks at how animals obtain and break down the food they eat. We begin at the cellular level, building on the biochemistry of metabolism discussed earlier (Chapter 7). Then, we examine the dietary needs and the organization and function of animal digestive systems: how an animal eats, digests, and absorbs food to supply its cells with the energy required for its function. The relationship between an animal’s diet and its place in an ecosystem is reserved until Chapter 47.