The immune system (AQA GCSE Biology): Revision Notes
The immune system
What is the immune system?
Your immune system is your body's defence network. When harmful microorganisms (called pathogens) enter your body, the immune system works to fight them off and keep you healthy.
The immune system is constantly working to protect you, even when you don't realise it. It can distinguish between your body's own healthy cells and foreign invaders that could cause harm.
White blood cells - your body's defenders
White blood cells are the main soldiers in your immune system. They defend your body against pathogens in three important ways:
1. Phagocytosis - the eating defence
Some white blood cells act like tiny vacuum cleaners. They:
- Swallow up harmful pathogens
- Move around the pathogen to surround it
- Break down and destroy the pathogen inside themselves
This process is called phagocytosis (meaning "cell eating").
Phagocytosis is like having microscopic guards that patrol your body, literally eating any harmful invaders they encounter. This is one of your body's first lines of defence against infection.
2. Antibody production - the targeting defence
Other white blood cells make special proteins called antibodies. Here's how they work:
- Each antibody is designed to stick to a specific part of a pathogen (called an antigen)
- When an antibody finds its matching antigen, it attaches to it
- This helps destroy the pathogen
- Each antibody only works against one specific type of pathogen
Antibody specificity is crucial: Each antibody is like a unique key that only fits one specific lock (antigen). This is why you need different antibodies for different diseases.
3. Antitoxin production - the poison defence
Some pathogens make harmful toxins (poisons). Certain white blood cells produce antitoxins that:
- Attach to the poisonous substances
- Make them harmless so they can't damage your body
How immunity works
When you get infected for the first time, your immune system creates memory cells. These special cells remember the pathogen for years.
Primary response (first infection)
- Takes longer to fight off the infection
- You usually get ill during this time
- Your body learns to recognise the pathogen
Secondary response (second infection)
- Happens much faster than the first time
- Creates more antibodies quickly
- You often don't get ill at all, or only mildly
Worked Example: Measles Immunity
After you've had measles once, memory cells in your blood remember the measles virus. If the virus tries to infect you again, these memory cells quickly produce lots of antibodies. This stops you getting measles again.
This is why measles vaccination works - it creates the same memory cells without you having to suffer through the actual disease.
Key terms to remember
- Pathogen: A harmful microorganism that causes disease
- Antigen: A substance on pathogens that antibodies recognise
- Antibody: A protein that sticks to specific antigens
- Memory cells: White blood cells that remember past infections
- Primary response: Your immune system's first reaction to a new pathogen
- Secondary response: Your immune system's faster reaction to a pathogen it has seen before
Key Points to Remember:
- Your immune system has three main defences: phagocytosis (eating germs), antibodies (targeting specific germs), and antitoxins (neutralising poisons)
- Antibodies are specific - each one only works against one type of pathogen
- Memory cells help you become immune to diseases you've had before
- The second time you meet the same pathogen, your immune response is faster and stronger
- This is why you usually only get diseases like measles once in your lifetime