1) Four main feeding mechanisms of animals a) Suspension feeders i) (1) Humpback whales b) Substrate feeders i)

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1 1 AP Biology March 2008 Digestion Chapter 41 Homeostatic mechanisms manage an animal s energy budget. 1) Four main feeding mechanisms of animals Suspension feeders (1) Humpback whales Substrate feeders (1) Moth larvae c) Fluid feeders (1) Mosquitoes d) Bulk feeders (1) Humans i Three types of bulk feeders: (1) Herbivores eat mainly autotrophs. (2) Carnivores eat other animals. (3) Omnivores eat both plants and animals. 2) Glucose regulation is an example of homeostasis. c) d) 3) Calorie imbalance

2 2 Diet must supply carbon skeletons and essential nutrients. 1) 2) 3) 4) must be obtained in preassembled form because the animal cannot produce them. About half of the 20 amino acids are required by animals Must be obtained from food. c) There are also essential fatty acids that animals cannot make and must ingest. Organic molecules required in small amounts. Simple inorganic nutrients required in small amounts. Four main stages of food processing 1) 2) 3) 4) Act of taking down food. Breakdown of food into small molecules capable of being absorbed by the cells of the body. Enzymatic hydrolysis is the reaction by which macromolecules are broken up. It involves the addition of water. body s cells take up small molecules from the digestive track. passing of undigested material from the digestive track. Types of digestion 1) Intracellular digestion 2) Extracellular digestion

3 3 3) Gastrovascular cavity 4) Complete digestive tracks (alimentary canals) The movement of food through the digestive system. 1) Food in the mouth Saliva lubricates the food to facilitate swallowing. Contains the enzyme salivary amylase, which hydrolyzes starch and glycogen into smaller polysaccharides and the disaccharide maltose. 2) Chewed food is shaped into a ball bolus. 3) The esophagus moves food from the pharynx down to the stomach through peristalsis. 4) The stomach s functions include storing food and secreting gastric juice. Gastric juice contains hydrochloric acid, which is very acidic. Breaks down the extracellular matrix of meat and plant materials. Kills most of the bacteria ingested with food. 5) Secreted in an inactive form called pepsinogen, activated by hydrochloric acid In the stomach. 6) The result of stomach digestion is acid chime. 7)

4 4 8) The first section of the small intestine is the duodenum. In the duodenum, the acid chime mixes with secretions from the pancreas, the gallbladder, and the intestinal wall itself. 9) Particular macromolecules are broken down in the small intestine by the following processes: The breakdown of starch and glycogen begins with salivary amylase in the mouth. In the small intestine, pancreatic amylases break starch, glycogen, and small polysaccharides into disaccharides. The breakdown of these disaccharides occurs at the wall of the intestinal epithelium, and the monosaccharides are quickly absorbed. Pepsin begins the breakdown of proteins in the stomach, and in the small intestine; trypsin and chymotrypsin break polypeptides into smaller chains. Dipeptidases, carboxypeptdase, and aminopeptidase break apart proteins into amino acids. c) The breakdown of nucleic acids is similar to that of proteins. In the small intestine, nucleases break them down into nucleosides, nitrogenous bases, sugars, and phosphate groups. d) Digestion of fats starts in the small intestine. Bile salts coat the fat droplets and keep them from clumping and lipase hydrolyzes them. 10) The epithelial lining of the small intestine has folds called villi, which in turn bear projections called microvilli 11) In each villus is a set of tiny blood vessels called capillaries and a lymph vessel called a lacteal, which absorbs small fatty acids. 12)

5 5 13) The capillaries and veins that drain the nutrients away from the villi all join the hepatic portal vessel, which brings them to the liver. 14) Some other hormones involved in digestion are: Gastrin Enterogastrone c) Secretin and cholecystokinin (CCK) 15) The large intestine, also called the colon, is connected to the small intestine by a sphincter. The point of the connection is the site of the cecum, a small pouch with an extension called the appendix. 16) The wastes become more solid as they travel along and form feces. 17) At the end of the colon is the rectum, where feces are stored until they are eliminated.

6 6 Adaptations of digestive systems are associated with diet. 1) A mammal s dentition is greatly correlated with its diet. Mammals have specialized dentition that best enables them to ingest their usual diet. 2) Herbivores generally have longer alimentary canals than carnivores. Why?