Edexcel GCSE Biology Topic 5 Health, disease and the development of medicines: a complete overview of pathogens, defences, immunisation and antibiotics

What Topic 5 actually demands

Health, disease and the development of medicines is a large, vocabulary-rich topic. The examiners test precise definitions (health, pathogen, antigen, antibody), the difference between non-specific and specific defences, the logic of immunisation, and why antibiotics target only bacteria. It also includes a core practical and several Biology-only statements on plant defences. This guide ties together the four dot-point pages, each with its own practice questions.

Health, disease and pathogens

Health is complete physical, mental and social well-being (the WHO definition), not just the absence of disease. Communicable diseases are caused by pathogens and can spread; non-communicable diseases (cancer, diabetes) cannot. Having one disease can raise susceptibility to others, for example a weakened immune system from HIV. The four pathogen types are viruses, bacteria, fungi and protists, each causing named diseases.

Spread, prevention and plant defences

Pathogens spread by contact, water, air, food, body fluids and vectors, and spread is reduced by hygiene, isolation, vaccination, vector control and clean water. Viruses follow the lytic pathway (bursting the cell) or the lysogenic pathway (hiding in the host DNA). STIs such as HIV spread through body fluids and are reduced by condoms. Plants defend with physical barriers (cuticle, cell wall, bark) and chemical defences, and plant diseases are detected by symptoms, distribution and lab tests.

Defences, immunisation and medicines

The body's first line is physical and chemical barriers (skin, mucus, cilia, stomach acid, lysozyme). The specific immune system uses lymphocytes to make antibodies against a pathogen's antigens, leaving memory cells for fast future responses. Immunisation uses a dead or inactive pathogen to trigger this without illness, giving immunity and herd immunity. Antibiotics kill bacteria by targeting their cell processes, not viruses, and new medicines pass through discovery, preclinical and clinical testing.

How Topic 5 is examined

• Definitions. Health, pathogen, antigen, antibody, communicable and non-communicable.
• Explanations. The immune response, how immunisation works, and why antibiotics only treat bacteria.
• Core practical. The antiseptic and antibiotic investigation, including clear-zone area calculations using $\pi r^{2}$.
• Application. Choosing control measures to match a disease's route of spread.

Check your knowledge

A mix of recall and application questions covering Topic 5. Attempt them under timed conditions, then check against the solutions.

1. State the WHO definition of health. (1 mark)
2. Name the four types of pathogen and give a disease caused by each. (4 marks)
3. State one physical and one chemical defence of the human body. (2 marks)
4. Explain the role of memory cells in immunity. (2 marks)
5. Explain how immunisation makes a person immune to a disease. (3 marks)
6. Explain why antibiotics cannot cure a cold. (2 marks)
7. A clear zone has a radius of $7\ mm$. Calculate its area using $\pi r^{2}$, to one decimal place. (2 marks)
8. Give two ways the spread of a water-borne disease can be reduced. (2 marks)