Ch 6 Nutrition in humans

Question 1

Swallowing

Answer 1

1. The tongue rises to push the bolus towards the pharynx
2. The soft palate moves up to prevent the bolus from entering the nasal cavity
3. The larynx rises, the epiglottis covers the opening to the trachea. This prevents the bolus from entering the trachea
4. The bolus enters the oesophagus

Question 2

Peristalsis

Answer 2

Behind the bolus:
Circular muscles contract and longitudinal muscles relax, causing the lumen to become smaller. This squeezes the food forward.
In front of the bolus:
Circular muscles relax and longitudinal muscles contract, causing the lumen to become larger. The food can slide through the lumen

Question 3

Bile salts

Answer 3

They emulsify lipids into small droplets. This facilitates chemical digestion by increasing the surface area to volume ration of lipids for lipase to act on.

Question 4

Absorption of water and water-soluble food molecules

Answer 4

Water-soluble food molecules are absorbed into the blood in the capillaries by diffusion and active transport. As absorption of digested food into the blood capillaries increases the water potential of contents in the small intestine, water is drawn into the blood by osmosis.

Question 5

Absorption of lipid and lipid-soluble food molecules

Answer 5

Fatty acids and glycerol enter the epithelium of the villi by diffusion. In the epithelial cells, they recombine into fine lipid droplets, which then enter the lymph in the lacteals of the lymphatic system.
Lipid-soluble vitamins are absorbed into the lymph in the lacteals by diffusion.

Question 6

Adaptation of small intestine for absorption

Answer 6

1. The small intestine is very long. This allows sufficient time for complete digestion and absorption
2. The inner wall of the small intestine is highly folded. There are many villi on the wall. Epithelial cells of the villi have a large number of microvilli. These increase the surface area for absorption
3. The epithelium is very thin, only one-cell thick. This provides a short distance for diffusion of food molecules into the blood. Absorption can take place rapidly.
4. The lacteal and the dense network of capillaries in the villi allow the absorbed food molecules to be carried away rapidly. A steep concentration gradient of food molecules is maintained across the wall of the small intestine. This increases the rate of diffusion of food molecules.
5. Peristalsis brings the digested food molecules into close contact with the villi for absorption. This keeps a steep concentration gradient of food molecules across the wall of the small intestine to increase the rate of diffusion of food molecules

Question 7

An in vitro method that allows a direct measurement of digestion of fat in laboratory

Answer 7

• Suitable substrate and enzyme: Prepare a mixture of lipase and oil
• Identification of parameter for measuring dependent variable: use a data logger with pH meter to show the change in pH of the mixture
• Expected results: The faster drop in pH of the mixture, the faster the digestion of fat