1.1. Lysozyme is an enzyme found in many secretions of the body, such as tears, saliva and milk. It is able to break down the peptidoglycan cell walls of bacteria and form part of the body's chemical defence system against pathogens.

Fig.1 shows a molecular model of lysozyme.

Fig. 1

With reference to Fig.1 and the parts labelled A and B, explain the term 'secondary structure'.

1.2. Enzymes, such as lysozyme, are described as being 'biological catalysts'.

Outline what is meant by the term 'biological catalyst'.

1.3. State whether lysozyme can be classified as an intracellular or extracellular enzyme and explain your answer.

1.4. Lysozyme molecules will eventually stop working and are broken down.

Outline how cells replace the enzymes that are broken down.