Biology IGCSE Edexcel - Biological Molecules, Enzymes and Food Tests

What are biological molecules?

Biological molecules are the building blocks to make cells and other key structures required to make living organisms. 

They are known as carbohydrates, lipids, and proteins

What are the chemical elements present in carbohydrates, lipids, and proteins

Carbohydrates = carbon, hydrogen and oxygen.

Lipids = carbon, hydrogen and oxygen.

Proteins = carbon, hydrogen oxygen, and nitrogen

What are carbohydrates, lipids, and proteins made up of?

Carbohydrates = made up of simple sugars e.g glucose

Lipids = made up of fatty acids and glycerol

Proteins = made up of amino acids

What is the test for starch?

Put a small sample of each food into the well of a spotting tile. 

Add a few drops of Iodine indicator solution. 

If the food goes blue/black then it contains starch.

What is the test for glucose?

Take a sample of the food to test an put it in a boiling tube.

Add Benedict’s solution.

Heat the boiling tube in a water bath at 80^oC for 5 minutes.

If it contains glucose it will change colour.

It goes from blue to green to orange and finally brick red depending on the amount of glucose.

What is the test for protein?

To test for protein you take the sample, to be tested and place it in a test tube. 

You then add Biuret solution. 

Buiret solution starts off as blue and will turn to lilac/purple if protein is present. 

What is the test for lipids?

To test for lipids you carry out the emulsion test. 

The food sample is placed in a test tube and a small volume of ethanol is added. 

The test tube is shaken and the fat dissolves into the ethanol. 

An equal volume of water is added. 

If a cloudy emulsion forms this indicates the presence of fats.

What are enzymes?

An enzyme is a biological catalyst that speeds up the rate of biochemical reactions without getting used up.

How do enzymes work?

Each enzyme has an active site.

The molecule that it wants to help change is called the substrate.

The active site fits the substrate like a lock and a key.