Correlative Digestive Systems • Unicellular organisms – cells in direct contact with extracellular environment – diffusion of nutrients / gases in and waste / gases out = easy • Multicellular organisms – most cells NOT in direct contact with extracellular environment– must have specialized structures for obtaining and breaking down food.
Animals = HeterotrophsAdapted for FEEDING and DIGESTING 5 Types of Feeders 1. Ingestive feeders - Use a mouth to take in food - E.g., Most animals – Foxes, Anteaters, and Snakes
2. Absorptive feeders • Absorb nutrients directly from extracellular fluid because they are parasitic, living in the digestive system of a host - E.g., Tapeworms and Flukes
3. Filter feeders - Collect small organisms and particles from the surrounding water - E.g., Oysters and Mussels
4. Substrate feeders - Eat the material through which they burrow - E.g., Earthworms and Termites
5. Fluid Feeder • - Pierce the body of a plant or animal and withdraw fluids. - E.g., Aphids and Mosquitoes
2 Types of Animal Body Plans: 1. Sac-like (Gastrovascular Cavity); • Found in many invertebrates Sea Anemone Flatworm Hydra
2. Tube-within-a-Tube (Mouth IN, Anus OUT); Vertebrates make use of this efficient body plan. This diagram shows the varying degree of complexity possible. Also common in some invertebrates such as Snails and Worms.