Summative Practice Chapter 9 – Question 5 & 6 (Form 4 Biology Textbook Exercise and Answer)

Question 5:
Explain the processes that fat molecules undergo starting from the duodenum until it is finally used by body cells.

• Lipid digestion begins in the duodenum.

• Bile salts produced by the liver emulsify fats into lipid droplets.

• Pancreas secretes pancreatic juice which contains lipase into the duodenum.

• Lipase hydrolyses lipid droplets to fatty acids and glycerol.

• Lipid + water Glycerol + fatty acids

• Absorption of fatty acids and glycerol occurs in the small intestine.

• In the epithelial cells of villi, the condensation of fatty acid and glycerol forms lipid.

• Lipid droplets are absorbed into the lacteals of villi.

• Lipid is transported from the lacteal by the lymphatic system into the thoracic duct and finally enters the blood flow through the left subclavian vein.

• Assimilation occurs in the cells.

• Cells use lipids to form the complex compounds of the plasma membrane.

Question 6:
A teenager had the following for his breakfast.

Explain what happens to the final digested products of his breakfast in his body cells.

• Bread contains carbohydrate. The digestion of carbohydrate produces glucose.

• Glucose is transported to body cells and the liver to be oxidised during cellular respiration to yield energy.

• Excess glucose is converted into glycogen for storage.

• The final product of butter is fatty acids and glycerol.

• Lipid is oxidised to produce energy.

• Some of the lipids are stored in adipose tissues.

• The final product of proteins (egg and milk) is amino acids.

• Amino acids are carried to body cells for enzyme synthesis and repair of damaged tissues.

• Apple and milk provide vitamin and mineral salts.

• Vitamins such as vitamin B are used as cofactors. Generally, vitamins and mineral salts maintain optimum health.

• Apple also provides undigested fibre that facilitates defaecation.

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