1. Ch. 21. Nutrition and Digestion
All animals must eat to provide
energy and
the building blocks used to assemble new molecules.
Animals also need essential
vitamins and
minerals.
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2. 21.2 Overview: Food processing occurs in four stages
Food is processed in four stages.
Ingestion is the act of eating.
Digestion is the breaking down of food into molecules small enough for the body to absorb.
Absorption is the take-up of the products of digestion, usually by the cells lining the digestive tract.
Elimination is the removal of undigested materials out of the digestive tract.
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3. Chemical digestion (hydrolysis) Nutrient molecules enter body cells
Figure 21.2A
Pieces of food
Small molecules
Mechanical digestion
Undigested material
Figure 21.2A The four main stages of food processing
Chemical digestion (hydrolysis)
Nutrient molecules enter body cells 1
Ingestion 2
Digestion 3
Absorption 4
Elimination 3

4. Protein- digesting enzymes
Figure 21.2B
Food Molecules
Components
Protein- digesting enzymes
Protein
Amino acids
Carbohydrate- digesting enzymes
Polysaccharide
Disaccharide
Monosaccharides
Nucleic-acid- digesting enzymes
Figure 21.2B Chemical digestion: the breakdown of large organic molecules to their components
Nucleic acid
Nucleotides
Fat-digesting enzymes
Fat
Glycerol
Fatty acids 4

5. 21.3 Digestion occurs in specialized compartments
Sponges digest food in vacuoles.
Most animals digest food in compartments.
Cnidarians and flatworms have a gastrovascular cavity with a single opening, the mouth.
Food enters the mouth.
Enzymes break down the food.
Food particles move into cells lining the compartment.
Undigested materials are expelled back out the mouth.
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6. 21.3 Digestion occurs in specialized compartments
Most animals have an alimentary canal with
a mouth,
an anus, and
specialized regions associated with one-way flow of food.
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7. 21.3 Digestion occurs in specialized compartments
The normal one-way flow moves food
into the pharynx or throat,
down the esophagus to a
crop where food is softened and stored,
gizzard, where food is ground and stored, and/or
stomach where food is ground and stored,
to the intestines, where chemical digestion and nutrient absorption occur, and finally
undigested materials are expelled through the anus.
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8. Digestive enzymes being released from a gland cell Tentacles
Figure 21.3A 1
Digestive enzymes being released from a gland cell
Tentacles
Mouth 2
Food digested to small particles
Food (a water flea) 3
A food particle being engulfed
Gastrovascular cavity 4
A food particle digested in a food vacuole
Figure 21.3A Digestion in the gastrovascular cavity of a hydra 8

9. Earthworm Mouth Pharynx Intestine Esophagus Anus Crop Gizzard
Figure 21.3B
Earthworm
Mouth
Pharynx
Intestine
Esophagus
Anus
Crop
Gizzard
Grasshopper
Esophagus
Midgut
Anus
Mouth
Crop
Hindgut
Gastric pouches
Figure 21.3B Three examples of alimentary canals
Bird
Stomach
Mouth
Gizzard
Intestine
Esophagus
Crop
Anus 9

10. THE HUMAN DIGESTIVE SYSTEM
THE HUMAN DIGESTIVE SYSTEM
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11. 21.4 The human digestive system consists of an alimentary canal and accessory glands
In humans, food is
ingested and chewed in the mouth or oral cavity,
pushed by the tongue into the pharynx,
Saliva begins breakdown of di- and polysaccharides
moved along by alternating waves of contraction and relaxation by smooth muscle in the walls of the canal in a process called peristalsis, and
moved in and out of the stomach by muscular ring-like valves called sphincters.
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12. 21.4 The human digestive system consists of an alimentary canal and accessory glands
Food is pushed by the pharynx into the esophagus, which connects to the stomach. In the stomach, enzymes begin digestion of proteins. Enzymes from the pancreas and bile (stored in gall bladder) from the liver are added to the small intestine where digestion is completed and nutrient absorption occurs.
Undigested materials move through the large intestine, feces are stored in the rectum, and then expelled out the anus.
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13. A schematic diagram of the human digestive system
Figure 21.4
Nasal cavity
Oral cavity (mouth)
A schematic diagram of the human digestive system
Tongue
Pharynx
Salivary glands
Oral cavity
Esophagus
Salivary glands
Esophagus
Liver
Gall- bladder
Esophagus
Stomach
Sphincters
Small intestine
Liver
Gall- bladder
Stomach
Pancreas
Figure 21.4 The human digestive system
Large intestine
Pancreas
Small intestine
Small intestine
Rectum
Anus
Large intestine
Key
Alimentary canal
Rectum
Accessory digestive glands
Anus 13

14. a. g. b. h. c. i. d. e. j. k. f. l. Figure 21.UN02
Figure 21.UN02 Connecting the Concepts, question 1 j. k. f. l. 14