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Digestive System

Digestive System - mussels collect small organisms and...

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Digestive System Single-celled organisms can directly take in nutrients from their outside environment. Multicellular animals, with most of their cells removed from contact directly with the outside environment, have developed specialized structures for obtaining and breaking down their food. Animals depend on two processes: feeding and digestion. Animals are heterotrophs , they must absorb nutrients or ingest food sources. Ingestive eaters , the majority of animals, use a mouth to ingest food. Absorptive feeders , such as tapeworms, live in a digestive system of another animal and absorb nutrients from that animal directly through their body wall. Filter feeders , such as oysters and
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Unformatted text preview: mussels, collect small organisms and particles from the surrounding water. Substrate feeders , such as earthworms and termites, eat the material (dirt or wood) they burrow through. Fluid feeders , such as aphids, pierce the body of a plant or animal and withdraw fluids. Ulcers Peptic ulcers result when these protective mechanisms fail. Bleeding ulcers result when tissue damage is so severe that bleeding occurs into the stomach. Perforated ulcers are life-threatening situations where a hole has formed in the stomach wall. At least 90% of all peptic ulcers are caused by Helicobacter pylori . Other factors, including stress and aspirin, can also produce ulcers....
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