6.3 Defence Against Infectious Disease

The diagram below shows the production and role of antibodies in the body.

Antibodies are produced by cell X.

Identify cell X.

[1 mark]

Antibodies are produced in response to the antigens present on pathogens.

Define the term 'antigen'.

[1 mark]

Antibodies aid the body in fighting pathogens in a number of different ways.

State one way in which they achieve this.

[1 mark]

Antibodies are short-lived, but memory cells remain to provide long term immunity against a second infection by the same type of pathogen.

Describe the secondary response of the memory cells during an infection by the same type of pathogen.

[2 marks]

The diagram below shows the action of penicillin on the bacterial cell wall.

Penicillin is an example of an antibiotic.

Define the term 'antibiotic'.

[1 mark]

Penicillin is an example of a commonly used antibiotic. It is produced naturally by a fungus (penicillium) to kill competing bacteria in their environment.

Based on the information in the diagram in part a), state the way in which penicillin kills bacteria.

[1 mark]

Other than the process stated at part b), list two processes in prokaryotic cells that antibiotics may target.

[2 marks]

Antibiotics are not effective against viruses since they lack the structure and mechanisms of prokaryotic cells. Certain viral diseases are treated with substances known as antivirals.

State the way in which an antiviral works.

[1 mark]

Skin is the largest organ of the body and forms part of the primary defence against pathogens.

List two ways in which the skin defends the body against pathogens.

[2 marks]

Platelets are very important in maintaining the integrity of broken skin as a barrier.

Define the term 'platelet'.

[1 mark]

Platelets are essential in the process of blood clotting.

State the role of platelets in response to blood vessel damage.

[1 mark]

One mark is available for clarity of communication throughout this question.

Human immunodeficiency virus (HIV) is mainly transmitted by the direct exchange of body fluids.

List four ways in which HIV can be transmitted between hosts.

[4 marks]

Once micro-organisms enter the body, white blood cells called phagocytes will provide the next line of defence.

Outline the way in which phagocytes provide defence against micro-organisms.

[4 marks]

An HIV infection will eventually progress into AIDS.

Outline the development of AIDS from an HIV infection.

[5 marks]