Proteins are an important part of a healthy diet because they provide essential amino acids. (a) State what is meant by an essential amino acid.

 There are 20 amino acids, and they can be classified as essential or non-essential – if they are non-essential they can be synthesised by the human body by itself, with no need to supplement them in the diet. If they are essential they cannot be synthesised by the body and must be obtained through dietary means.