Feeding and Digestion – Part 1

Biology 155Spring 2010

B. L. Krilowicz

I. Definitions

A. Ingestion = to bring food into the digestive system

B. Digestion = to break food down into smaller molecules that can be absorbed by the body

1. Mechanical – physical, makes use of chewing, grinding, etc.

2. Chemical - makes use of enzymesC. Egestion = elimination of non-digestible

materials

II. Feeding Mechanisms:

A. Feeding on food dissolved (stays in solution) in the environment –

1. Rare2. Animal takes up food across body surface3. No need for a digestive system(Note that this mechanism is not mentioned in

the textbook.)

Examples -

a. Tapeworms -

Marine invertebrates

B. Feeding on liquids –

1. Requires a specialized mouthpart to obtain fluids

2. Mouthparts are adapted for sucking or lapping

3. Other examples –

Plant sap – aphids

Blood – mosquitoes and vampire bats

Milk – young mammals

Lapping

Sucking

Nectar as food source (also hummingbirds)

Fig. 21.1C

a. sponges

C. Filter Feeding = feeding on small particles suspended (will settle out) in the environment

1. Must be aquatic

2. Requires specialized straining device

3. Continuous feeders

4. Indiscriminant feedersc. Other examples – baleen whale, mollusks

Fig. 21.1A

D. Feeding on Large Particles –

1. Requires elaborate sensory systems to find prey

2. Requires elaborate motor systems to capture prey

3. Discontinuous feeders

4. Highly selective

Ex. Fish to mammals, insects

Figs. 21.1B (substrate feeders) and 21.1D

III. Intracellular versus Extracellular Digestion:

A. Intracellular = engulf (phagocytize) food particle and isolate it in a food vacuole inside a cell; digestive enzymes are secreted into the vacuole, where chemical digestion occurs

Problem = food must be smaller than a cell

Ex. Sponges and single celled organisms

III. Intracellular versus Extracellular Digestion - continued

B. Extracellular = digestive enzymes are secreted into a cavity where chemical digestion generates small molecules that can be absorbed into the body

Advantage = can eat things larger than the size of a single cell

1. Gastrovascular Cavity = Incomplete Digestive SystemProblem = ingestion and egestion occur at the same site, thus

regional specialization is impossible which reduces digestive efficiency

Ex. Jellyfish and their relatives (shown)

Flatworms (not shown)

Fig. 21.3A

2. Complete Digestive System = a True Gut, system with both a mouth and an anus

Advantage = one-way traffic of food bolus, thus regional specialization is possible which increases digestive efficiency

Ex. Roundworms (shown here) through mammals (not shown)

Fig. 21.3B

IV. Example of a Generalized Complete Digestive Tract:

Mouth

Oral cavitySalivary glands

esophagus

Stomach or crop and gizzard

liver

Gall bladder pancreas

Small intestineLarge intestine

Anus

Fig. 21.4