The Different Feeding Methods Of Animals

Endocytosis, Filter Feeding, Fluid Feeding And Seizing Prey

Jun 10, 2009

Whether they absorb molecules across the body surface or swallow live prey, all animals must get their energy from a food source. Here are the ways they do this.

All animals need energy to grow, maintain their health and reproduce. Energy used in metabolism comes from food, but what constitutes food can vary depending on the animal.

Food Absorption Through the Body Surface

Many protozoans (single-celled organisms), endoparasites and aquatic invertebrates (animals without a backbone) take up nutrients from the surrounding medium via the soft body wall. For example, endoparasites, such as tapeworms, are surrounded by the tissue of their host, which they absorb and feed off.

Endocytosis

Endocytosis is a more active form of feeding compared with absorption across the body wall. It occurs at the local cellular level rather then the tissue level. Two examples are:

Filter Feeding (Suspension Feeding)

Many aquatic animals are filter feeders. They capture food suspended water (e.g., phytoplankton), using specialized devices or ‘traps’. Many filter feeders are sessile (non moving) organisms, such as sponges and bivalve mollusks, so they rely on the current to bring their food past.

On a larger scale, baleen whales are also filter feeders. These whales have plates in their mouths bearing a fringe of filaments, which act as strainers, trapping krill and other crustaceans, as the whale swims with its mouth open. When the whale closes its mouth, water is forced out, and the crustaceans are left behind and swallowed.

Fluid Feeding

Fluid feeders pierce, suck, cut or lick as a way of taking up fluid, usually the blood of their prey. For example, leeches are filter feeders who use an anticoagulant from their saliva to prevent their prey’s blood from clotting. Leeches penetrate the body wall with a protrusible (protrudes out) pharynx through which they suck the prey’s blood.

Seizing Prey

Predators that use teeth, mouthparts, claws or other appendages to capture and immobilize prey fall under this category. This group would include lobsters with their claws, one modified for tearing, one for crushing, mammals that seize and masticate their prey with their teeth, as well as many birds with sharp beaks that probe or tear and claws or talons for grasping.

Herbivory and Grazing

Most herbivores have mouthparts suitable for grazing on plant material. Small sea snails for example, have a tooth like structure called a radula that they use to scrape off algae from rocks. Larger herbivores have flattened teeth specialized for grinding plants.

Silverthorn, D.U, 2007, ‘Acquiring Energy: Feeding, Digestion and Metabolism’, in Human Physiology, ed. Benjamin Cummings, San Francisco, chap. 15.

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