What causes communicable diseases, and how does the body defend itself?
Communicable diseases and their pathogens, how pathogens spread, the body's defences, the immune response and the role of antibodies, and vaccination.
A focused answer to Edexcel GCSE Combined Science Topic 5 (CB5), covering communicable diseases and the four types of pathogen, how pathogens spread, the body's physical and chemical defences, the immune response and antibodies, and how vaccination works.
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What this dot point is asking
Edexcel wants you to describe communicable diseases and the four types of pathogen, explain how pathogens spread, describe the body's defences, explain the immune response and the role of antibodies, and explain how vaccination protects people.
Communicable diseases and pathogens
Examples include cholera (a bacterium), influenza and HIV (viruses), rose black spot (a fungus) and malaria (a protist, spread by mosquitoes). Bacteria can make you ill by releasing toxins that damage cells; viruses reproduce inside cells and burst them.
How pathogens spread
Pathogens spread by:
- Air (droplets when you cough or sneeze, for example influenza).
- Water (drinking contaminated water, for example cholera).
- Direct contact (touching, for example athlete's foot, or through body fluids for HIV).
- Vectors (animals that carry pathogens, for example mosquitoes spreading malaria).
Spread can be reduced by hygiene, isolating infected individuals, destroying vectors, and vaccination.
The body's defences
The immune response
If a pathogen gets past the barriers, white blood cells respond:
- Phagocytes engulf and digest pathogens (phagocytosis).
- Lymphocytes produce antibodies, proteins with a specific shape that lock onto the antigens on a pathogen, marking it for destruction and making pathogens clump together.
- Lymphocytes also produce antitoxins that neutralise toxins.
Each pathogen has unique antigens, so a specific antibody is needed for each one. After an infection, memory cells remain, giving long-term immunity.
Vaccination
A vaccine contains a dead or inactive form of a pathogen, or its antigens. It triggers the lymphocytes to make antibodies and memory cells without causing the disease. If the real pathogen later enters, the memory cells produce the correct antibodies faster and in larger amounts, destroying it before it causes illness. When a large proportion of a population is vaccinated, the spread of the disease is greatly reduced (herd immunity).
Try this
Q1. Name the four types of pathogen. [2 marks]
- Cue. Bacteria, viruses, fungi and protists.
Q2. State the role of antibodies. [1 mark]
- Cue. They lock onto specific antigens on a pathogen, marking it for destruction.
Exam-style practice questions
Practice questions written in the style of Pearson Edexcel exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
Edexcel 20194 marksDescribe how white blood cells defend the body against a pathogen that has entered the blood.Show worked answer →
A 4-mark describe question on the immune response.
Some white blood cells (phagocytes) engulf and digest the pathogens (1 mark). Other white blood cells (lymphocytes) produce antibodies, which are specific to the antigens on the pathogen and cause the pathogens to clump together and be destroyed (2 marks). White blood cells also produce antitoxins that neutralise toxins released by bacteria (1 mark).
Markers reward phagocytosis, the production of specific antibodies against antigens, and antitoxins. Naming the cells is helpful but the processes earn the marks.
Edexcel 20214 marksExplain how a vaccine protects a person from a disease, and why a vaccinated person usually does not become ill if they later meet the pathogen.Show worked answer →
A 4-mark explain question on vaccination and immunity.
A vaccine contains a dead or inactive (weakened) form of the pathogen, or its antigens (1 mark). This makes the white blood cells (lymphocytes) produce antibodies against the antigen without the person becoming ill (1 mark). Memory cells are produced and remain in the body (1 mark). If the same pathogen enters later, the memory cells make the correct antibodies very quickly and in large amounts, destroying the pathogen before it can cause disease (1 mark).
Markers reward the inactive antigen, the first antibody response, memory cells, and the faster, larger second response.
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Sources & how we know this
- Edexcel GCSE (9-1) Combined Science (1SC0) specification — Pearson (2016)