Biology Practical Revision

Sugars

For reducing sugars- add Benedict's reagent(copper(ii) sulphate in an alkaline solution) and heat. The Cu2+ ions in the reagent will be reduced to Cu, which is a colour change from blue to red.

For non-reducing sugars- add acid to the test substance and heat to hydrolyse any glycosidic bonds present. Then, neutralise it by adding an alkali such as sodium hydroxide. Now, perform the reducing sugars test. If a colour change occurs, a non-reducing sugar is present.

Starch

Add iodine solution to the test substance. If starch is present, there will be a colour change from orange-brown to blue-black. 

Lipids

Lipids are insolube in water but soluble in ethanol.

The test substance is shaken with some ethanol, allowing any lipids to dissolve in the ethanol. The ethanol with dissolved substance is then poured into water.

If no lipid is present, the ethanol just mixes with the water.

If a lipid is present, it will not dissolve in the water, and an emulsion is formed (a white and cloudy substance).

Proteins have amine NH2 groups, which can react with copper ions to form a complex that has a strong purple colour.

Biuret reagent(copper(ii) sulphate and NaOH or KOH) is added to the test substance. 

If protein is present, a colour change will occur from blue to purple.

Microscope Work 

Magnification = size of the image/actual size of specimen

Resolution = the ability to distinguish between separate points. Max. resolution of a light microscope is 200nm.

1000nm = 1μm

1000μm = 1mm

To measure the rate of a reaction:

- the time taken for the reactants to be used up and disappear

- the time taken for products to appear