Carbohydrate Digestion

starch,sucrose and lactose digestion, plus lactose intolerance and the test for starch.

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Starch Digestion

Food is taken into the mouth and chewed by the teeth.This breaks it into small pieces,giving it a large surface area.

Saliva enters the mouth, and is thoroughly mixed with the food. Saliva contains salivary amylase, this starts hydrolysing any starch in the food to maltose.

The food is swallowed and enters the stomach, where the conditions are acidic. This acid denatures the amylase and prevents further hydrolysis of the starch.

The food then passes into the small intestine, where it mixes with pancreatic juice.The pancreatic juice contains pancreatic amylase. This continues the hyrdrolysis of any remaning starch to maltose.

Muscles in the intestine wall push the food along the small intestine.ITs lining produces maltase. This hydrolyses maltose into glucose.

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Sucrose + Lactose Digestion

Sucrose passes through the stomach and into the small intestine, whose epithelial lining produces sucrase.

Sucrase hydrolyses the singly glycosidic bond in the sucrose molecule to produce the two monosaccharides that make up sucrose - glucose and fructose.

Lactose is digested in the small intestine by the enzyme lactase.

 Lactase hydrolyses the glycosidic bond that links glucose and galactose (the monomers that make up lactose)

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Lactose Intolerance

Lactose is a sugar that is found in milk.It is digested by an enzyme called lactase, which is found in the small intestine.

If you don't have enough lactase, you won't be able to break down lactose in milk.This is called lactose intolerance.

Undigested lactose is fermented by bacteria and can cause stomach cramps, excessive wind and diarrhoea.

Millk can be treated with purified lactase to make it suitable for lactose-intolerant people.

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Test for starch

you add iodine dissolved in potassium iodide solution.

If starch is present, the sample changes from browny-yellow to a dark, blue-black colour.

If no starch is present, the sample will stay browny-yellow.

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1 star? i copied these out of the aqa textbook!!

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