Defences, the immune system and vaccination
The body has two lines of protection. Physical and chemical barriers keep most pathogens out; if some get in, white blood cells destroy them. Vaccination prepares the immune system in advance.
Part 1 of 3: Learn it
In short
- Skin, the nose, the trachea and the stomach all stop pathogens getting in or surviving.
- White blood cells engulf pathogens, make antibodies and make antitoxins.
- A vaccine contains a dead or inactive form of a pathogen, so the body is ready to respond quickly next time.
Where this is in your specification
Spec points: AQA 4.3.1.6 and 4.3.1.7 (Combined Trilogy 4.3.1.6 and 4.3.1.7), Edexcel Topic 5, OCR B5.2
| Board | Topic: Infection and response |
|---|---|
| AQA 8461 | 4.3 (8461); 4.3 (8464) |
| Edexcel 1BI0 | Topic 5 |
| OCR J247 | B5 |
| Eduqas C400 | 3.1 to 3.3 |
| Cambridge IGCSE 0610 | 10.1, 15.1 |
| National 5 C807 75 | Multicellular organisms: 6 Transport systems in animals (blood and pathogens) |
Non-specific defences
| Defence | How it helps |
|---|---|
| Skin | a tough barrier; also makes antimicrobial secretions |
| Nose | hairs and mucus trap particles that may carry pathogens |
| Trachea and bronchi | sticky mucus traps pathogens and cilia sweep it up to the throat |
| Stomach | hydrochloric acid kills most pathogens swallowed with food |
White blood cells
- Phagocytosis: some white blood cells engulf a pathogen and digest it.
- Antibodies: proteins that lock onto the antigens on one particular pathogen, marking it or clumping pathogens together so they are destroyed.
- Antitoxins: proteins that neutralise the toxins released by bacteria.
Vaccination
A vaccine puts a small amount of a dead or inactive pathogen into the body. White blood cells respond by making antibodies, and memory cells stay in the blood. If the real pathogen arrives later, antibodies are made much faster and in greater numbers, so it is destroyed before you feel ill.
When most of a population is vaccinated, a pathogen struggles to spread, which also protects people who cannot be vaccinated. This is called herd immunity.
How does the stomach help defend against pathogens?
Show the answer
It makes hydrochloric acid, which kills most pathogens in food.
Part 2 of 3: See it worked
Worked examples
Example 1
Explain why a person who had chickenpox as a child is unlikely to catch it again.
- During the first infection, white blood cells made antibodies against the chickenpox virus
- Memory cells stayed in the body afterwards
- On a second infection they make the right antibodies quickly, before symptoms develop
Answer: Memory cells allow a fast, large antibody response, so the virus is destroyed before it can make the person ill.
Example 2
After a first vaccination, antibody levels peak at 10 units. After a booster they peak at 100 units. How many times higher is the second peak?
- 100 ÷ 10 = 10
Answer: 10 times higher.
Common mistakes
- Saying antibodies eat pathogens. Phagocytes engulf pathogens; antibodies bind to them.
- Saying a vaccine contains antibodies. It contains a dead or inactive pathogen (or parts of one).
- Mixing up antibodies (bind to antigens) and antitoxins (neutralise toxins).
- Saying cilia trap pathogens. The mucus traps them; the cilia move the mucus.
What do antitoxins do?
Show the answer
They neutralise the toxins released by bacteria.
Part 3 of 3: Test yourself
Check yourself
Answer each one in your head or on paper first, then open it to check.
How does the stomach help defend against pathogens?
It makes hydrochloric acid, which kills most pathogens in food.
What do antitoxins do?
They neutralise the toxins released by bacteria.
What does a vaccine contain?
Pathogens (or parts of them) that have been killed or made harmless, so they cannot cause the disease.
Jobs that use this
- Nurse (se abre en otra pestaña)
- Biomedical scientist (se abre en otra pestaña)
- Pharmacologist (se abre en otra pestaña)
Each link opens the job profile on the National Careers Service (England). In the rest of the UK: My World of Work (Scotland), Careers Wales, nidirect careers (Northern Ireland).
Estos apuntes están en inglés porque siguen los programas de examen del Reino Unido.
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