Biology - Unit 4: Biological Molecules

what chemical elements make up carbohydrates?

• carbon

• oxygen

• hydrogen

what chemical elements make up proteins?

• carbon

• oxygen

• hydrogen

• nitrogen

what chemical elements make up lipids?

• carbon

• oxygen

• hydrogen

what chemical elements make up DNA?

• carbon

• oxygen

• hydrogen

• nitrogen

• phosphorous

what smaller molecules make up starch, cellulose and glycogen?

glucose

what smaller molecules make up lipids?

fatty acids and glycerol

what smaller molecules make up proteins?

polypeptides → amino acids

what smaller molecules make up DNA?

nucleotides

what test can be done to test for the presence of starch?

iodine test

• add drops of iodine solution to food sample

• if positive, solution turns from orange-brown to blue-black

• if negative, solution remains orange-brown

what test can be done to test for the presence of reducing sugars?

benedict’s test

• add benedict’s solution into sample solution in test tube

• heat at 60-70℃ in water bath for 5 minutes

• take test tube out of water bath and observe the colour

• if positive, solution changes from blue to orange or brick red ppt.

• if negative, solution remains blue

what test can be done to test for the presence of proteins?

biuret test

• add drops of biuret solution to food sample

• if positive, solution changes from blue to purple

• if negative, solution remains blue

what test can be done to test for the presence of lipids?

ethanol emulsion test

• food sample is mixed with 2cm³ of ethanol and shaken

• ethanol is then added to an equal volume of cold water

• if positive, cloudy emulsion will form