6 Human Nutrition
(a) Structure P: X 1m
Structure R: Z 1m
It is because saliva present in structure P (mouth cavity) contains salivary amylase,
which catalyses the breakdown of starch into maltose.
/ Saliva does not contain enzymes for the breakdown of proteins and lipids. 1m
Gastric juice present in structure R (stomach) contains pepsin,
which catalyses the breakdown of proteins into peptides.
/ Gastric juice does not contain enzymes for the breakdown of carbohydrates and lipids. 1m
(b) The oil will be emulsified into small droplets. 1m
(c) Due to the blockage of the pancreatic duct, pancreatic lipase cannot reach the duodenum. 1m
Lipids cannot be completely digested. Some of them cannot be absorbed and thus
appear in the faeces. 1m
(d) Structure T is very long. 1m
This allows sufficient time for complete absorption. 1m
(a) The concentration of glucose in the blood in Y is higher than that in X.
Glucose from the breakdown of starch in the rice is absorbed into the capillaries in the villi
of the small intestine and transported to the liver via the hepatic portal vein (Y).
Thus, the concentration of glucose in the blood in Y increases.
The excess glucose in the blood is converted to glycogen in the liver.
Therefore, the concentration of glucose in the blood in the hepatic vein (X) does not change
after the person ate the rice.
(b) Liver produces bile, which is a digestive juice.