27.1 Feeding and Digestion

Most filter feeders catch algae and small animals by using modified gills or other structures as nets that filter food items out of water. Detritivores feed on detritus. Carnivores eat other animals. Herbivores eat plants or parts of plants. Nutritional symbionts rely upon symbiosis.

Some invertebrates break down food primarily through intracellular digestion, but many animals use extracellular digestion.

Carnivores typically have sharp mouthparts or other structures that capture food, hold it, and cut it into small pieces. Herbivores typically have mouthparts adapted to rasping or grinding.

• intracellular digestion (784)

• digestive tract (784)

• extracellular digestion (784)

• rumen (786)

• gastrovascular cavity (784)

27.2 Respiration

Respiratory structures provide a large surface area of moist, selectively permeable membrane and maintain a difference in the concentrations of oxygen and carbon dioxide on either side of the respiratory membrane, promoting diffusion.

Many aquatic invertebrates and most aquatic chordates other than reptiles and mammals exchange gases through gills. Aquatic reptiles and aquatic mammals, such as whales, breathe with lungs and must hold their breath underwater.

Respiratory structures in terrestrial invertebrates include skin, mantle cavities, book lungs and tracheal tubes. Terrestrial vertebrates breathe with lungs.

• gill (788)

• lung (788)

• alveolus (790)

27.3 Circulation

In an open circulatory system, blood is only partially contained within blood vessels. In a closed circulatory system, blood circulates entirely within blood vessels.

Most vertebrates with gills have a single-loop circulatory system with a single pump that forces blood around the body in one direction. Most vertebrates that use lungs for respiration have a double-loop, two-pump circulatory system.

• heart (791)

• atrium (792)

• open circulatory system (791)

• ventricle (792)

• closed circulatory system (792)

27.4 Excretion

Animals either eliminate ammonia from the body quickly or convert it into other nitrogenous compounds that are less toxic.

Aquatic animals allow ammonia to diffuse out of their bodies into surrounding water.

Some terrestrial invertebrates, including annelids and mollusks, produce urine in nephridia. Other terrestrial invertebrates, such as insects and arachnids, convert ammonia into uric acid. Mammals and land amphibians convert ammonia into urea. Most reptiles and birds convert ammonia into uric acid.

• excretion (794)

• nephridium (797)

• kidney (795)

• Malpighian tubule (797)

Think Visually Fill in the table below showing different types of animals and their differing respiratory structures.

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