2 examples = Maltose and Sucrose 

Maltose = 2 glucose molecules produced when amylase breaks down starch

Sucrose = Form in which sugar is transported around the plant

The monomers which make up disaccharides =

- Glucose joined to glucose forms maltose

- glucose joined to fructose forms surcose

- glucose joined to galactose forms lactose

Disaccarides need to be digested before they can produce energy sugars are often stored in this form.

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Benedicts test

Oil rig = oxidation is lost reduction is gain (of electrons)

The Benedicts test= shows the relationship between the concentration of reducing sugars.

The differences in colour mean that the benedicts test is semi-quantitative.

colours for the benedicts test=

green =none, yellowish green = very low,  yellowish brown= low, dark brown = medium, red= high

 Benedicts reagent turns red when heated with a reducing sugar beacuse the sugar gains more electrons making the bonds stronger.

another way of testing this is the starch test

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Monosaccharide functions

Gulcose = Main sugar used for respiration starch and glycogen are polymers of glucose is absorbed and transported in the blood in the blood stream to cells

Galactose = mainly in our diet as part of lactose of lactose disaccharide

fructose = sugar found naturally in fruit, honey and some vegetables

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Carbohydrates - polysaccharides

key words






glycosdic bonds

condensation reaction

hydrolysis reaction

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carbohydrates and polysaccharides

monosaccharides = glucose, glactose,fuctose

Disaccharides = maltose, lactose, sucrose

polysaccharides = starch, glycogen, cellulose

ploysaccharides are polymers containing many monosaccharides linked y glycosiolic bonds. like disaccharides polysaccharides are formed by condensation reactions

the major polysaccharides are starch and cellulose in plants and glycogen in animal.

As polysaccharides are very large they are insoluble =used for storage

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Test for starch

starch is easily detectable by its ability to change colour of the iodine in a potassium iodine solution from yellow to blue- black the test is carried out at room temperature

Place 2cm cubed of the sample being tested into a test tube (or 2 drops on a spotting tray)

Add 2 drops of iodine solution and shake or stir

The presence of starch is indicated by a blue- black coloration

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