[f.3 biology] digestion

1. A, C, D
2. Bile is a mixture of bile salts(hydrocarbon chain+ionic head, i.e. hydrophillic head and hydrocarbon tail), bile pigments, cholesterol and alkaline salts(NaHCO3). Its alkaline nature neutralizes the acidic chyme and provides an environment suitable for the action of digestive enzymes in the duodenum. The bile salts lower the surface tension of lipid molecules and emulsify them into fine droplets. This physical process is known as emulsification, in which bile salts combine with large lipid molecules to form water-soluble micelles. This results in provision of a large surface for lipase to act upon. The large lipid molecule, upon emulsification, turns into water-soluble micelles.

For reference:Bile pigments come from the breakdown of haemoglobin molecules in the liver. They give bile the characteristic yellow-green colour.

2010-06-17 18:46:18 補充：
Haemoglobin = Fe, alpha-chain, beta-chain, bile pigment, prosthetic group-haem

2010-06-19 20:35:20 補充：
John...係咪MJ
唔好意思...第一條係D...笑納^^~~

1D
bile dose not contain enzymes
gastric juice is acidic
saliva, pancreatic juice and intestinal juice fit the requirements.

2 bile contain bile salt, bile pigment, sodium hydrogencarbonate
there is no enzyme in bile. the substance in bile that helps digestion is bile salt, that can emulsify lipids into droplets to let pancreatic lipase digest lipid more easily.
sodium hydrogencarbonate provide a alkaline medium for pancreatic lipase, and protect duodenum from being harmed by hydrochloric acid from the stomach.
bile pigment is broken down from dead red blood cells. it is a waste

1,應該係A

2, 我只係知道Bile is produced by the liver and stored in the gall bladder. Bile helps to emulsify fats ibto smaller oil droplet. It can also neutralize stomach acid.

而enzyme既我記得pancreatic juice會有,,不過bile有冇就唔記得-0-

第2題唔係好幫到你,,s0r,