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Biology 2 /SL Review Book Topic 6: Human Health and Physiology
Name __________________________
Review Book Topic 6.1: Digestion
Key facts
1. Food ingested must be digested in order to be useful to the organism. Without digestion the food
particles are too large to be absorbed through the villi of the small intestine to enter the
bloodstream.
2. Large macromolecules of food go through hydrolysis allowing the organism to obtain necessary
building blocks for assimilation. This hydrolysis is also necessary so that ATP formation from the
food is possible.
3. Assimilation is the process by which the products of food digestion become part of the organism’s
body.
4. Enzymes greatly aid the digestive process by causing it to proceed more rapidly.
5. Specific enzymes are produced at particular locations of the digestive system. These enzymes act on
certain substrates to bring about digestion.
6. Digestive areas of particular activity involving enzymes include the mouth, the stomach and the
small intestine.
7. Enzymes which are active in the stomach must have optimum pH values which are quite acidic.
Enzymes working in the small intestine must be able to work in a more alkaline environment.
8. The mouth’s major enzyme producing glands are the salivary glands. The mouth has a pH of near 7.
9. The salivary glands produce salivary amylase which allows hydrolysis of starch into maltose.
10. The wall of the stomach produces the enzyme pepsin which breaks proteins down into small
polypeptides. The stomach has a pH of near 1.5.
11. The pancreas may function as an endocrine and as an exocrine gland. When it functions as an
exocrine gland it produces several enzymes. One is pancreatic lipase, which is transported to the
small intestine where it catalyzes the breakdown of triglycerides (fats or oils) into fatty acids and
glycerol. The pH of the small intestine is 7 or higher (slightly alkaline).
12. Digestion of proteins begins in the stomach. Also, the extremely acidic environment of the stomach
serves to destroy any incoming bacteria with the food.
13. Most of the digestion of food actually occurs in the small intestine. Enzymes active in small intestine
come from the pancreas and the walls of the structure itself.
14. Once digestion in the small intestine is finished, the smaller food products are absorbed through
millions of villi lining the interior of the small intestine. This absorption occurs as a result of
diffusion, facilitated diffusion, or active transport.
15. Villi bring about the process of absorption. They are small finger-like projections from the small
intestine wall. They are effective in food absorption due to their extreme numbers, large surface
area due to microvilli, capillaries near their surface and a centrally located lacteal which allows
absorption of fat digestion.
16. The indigestible parts of food mixed with large amounts of water pass to the large intestine.
17. In the large intestine water is absorbed and indigestible parts of the food are passed as feces
through the anus.
18. The parts of the digestive system that food passes through are the mouth, esophagus, stomach,
small intestine, large intestine and anus. The liver, pancreas and gall bladder are ancillary structures
involved in the digestive process.
ADDITIONAL NOTES
Biology 2 /SL Review Book Topic 6: Human Health and Physiology
Name __________________________
DRAW ASSESSMENT STATEMENTS
1. Draw and label a diagram of the digestive system. Include the following structures: mouth,
esophagus, stomach, small intestine, large intestine, anus, liver, pancreas, and gall bladder.
1. Why is the digestion of large food molecules essential?
2. What role do enzymes play in digestion?
Biology 2 /SL Review Book Topic 6: Human Health and Physiology
Name __________________________
3. Outline the source, substrate, products, and optimum pH conditions for salivary amylase, pepsin, and
pancreatic lipase.
4. Outline the function of the following in digestion:
Stomach –
Small intestine –
Large intestine –
5. Distinguish between absorption and assimilation.
6. Explain how the structure of the villus is related to its role in the absorption and transport of the
products of digestion.
7. List four structures within the digestive system that increase the efficiency of absorption of nutrients.