What are microorganisms, how does the body defend against disease, and how do vaccines work?
The main types of microorganism and their useful roles, pathogens and how they spread, the body's first-line defences, the role of white blood cells in phagocytosis and antibody production, and how vaccination gives immunity.
A focused CCEA GCSE Double Award Science (Biology Unit B2) answer on microorganisms and defence, covering the types of microorganism and their uses, pathogens and how they spread, first-line defences, white blood cells and phagocytosis and antibodies, and how vaccination provides immunity.
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What this dot point is asking
CCEA Double Award wants the types of microorganism and their useful roles, what pathogens are and how they spread, the body's defences, how white blood cells work, and how vaccination gives immunity. The immune response and vaccination are the high-mark topics.
Types of microorganism and their uses
The three main microorganisms are bacteria, viruses and fungi. Many are useful: bacteria are used to make yoghurt and cheese, yeast (a fungus) is used in bread and brewing, and microorganisms are used in biotechnology to make products such as antibiotics and insulin. To grow microorganisms safely, scientists use aseptic technique to avoid contamination.
Pathogens and how they spread
Reducing spread relies on hygiene: washing hands, covering coughs, cooking food properly and treating water.
First-line defences
The body has barriers that stop pathogens entering. The skin is a physical barrier; mucus in the airways traps pathogens and cilia sweep it away; stomach acid kills pathogens in swallowed food; and blood clots seal wounds. These work before the immune system is needed.
White blood cells
If pathogens get past the barriers, white blood cells defend the body in three ways:
- Phagocytosis: some white blood cells engulf and digest the pathogens.
- Antibodies: other white blood cells produce antibodies, proteins that lock onto the antigens (markers) on a specific pathogen, destroying it or marking it for destruction.
- Antitoxins: some neutralise the toxins released by pathogens.
Vaccination and immunity
After vaccination, memory cells stay in the body. If the real pathogen invades later, the memory cells make antibodies quickly and in large amounts, destroying the pathogen before it causes illness - this is immunity. When most of a population is vaccinated, the disease cannot spread easily, protecting even the unvaccinated (herd immunity).
Examples in context
Example 1. Why flu vaccines change each year. Flu viruses mutate, changing their antigens, so old antibodies and memory cells no longer fit. A new vaccine is made to match the current strains, showing how specific the immune response is.
Example 2. Herd immunity for measles. When a high proportion of children are vaccinated against measles, the virus cannot find enough non-immune people to spread to, so even babies too young to be vaccinated are protected. This shows immunity protecting a population, not just individuals.
Try this
Q1. Name the process where a white blood cell engulfs a pathogen. [1 mark]
- Cue. Phagocytosis.
Q2. What does a vaccine contain? [1 mark]
- Cue. A dead or weakened form of the pathogen.
Exam-style practice questions
Practice questions written in the style of CCEA exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
CCEA-style4 marksDescribe two ways white blood cells defend the body against pathogens.Show worked answer →
Two named defences with detail for four marks.
Some white blood cells carry out phagocytosis: they engulf and digest the pathogens.
Other white blood cells produce antibodies: proteins that lock onto the antigens on a specific pathogen and destroy it or mark it for destruction.
Some also produce antitoxins to neutralise the toxins made by pathogens. Markers reward phagocytosis described and antibody production described.
CCEA-style4 marksExplain how a vaccine makes a person immune to a disease.Show worked answer →
Trace the immune response to a vaccine for four marks.
A vaccine contains a dead or weakened form of the pathogen (its antigens).
White blood cells respond by producing antibodies against those antigens.
Memory cells are also made and stay in the body.
If the real pathogen invades later, the memory cells produce antibodies quickly and in large amounts, so the person does not become ill. Markers want antigens, antibodies, memory cells, and a fast response next time.
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Sources & how we know this
- CCEA GCSE Science Double Award specification — CCEA (2017)