- Define and explain Meet the Pathogens in your own words
- Use key terms such as pathogen accurately
- Apply what you have learned to new examples and questions
- Avoid the common mistakes learners make with this topic
Every day your body fights off invaders you never notice. In this chapter you will meet the four main types of pathogen, discover the layered defences that protect you, learn how vaccines train your immune system, and see how everyday choices shape your long-term health.
This lesson focuses on Meet the Pathogens: meet bacteria, viruses, fungi and protists and find out how they make us ill.
Meet bacteria, viruses, fungi and protists and find out how they make us ill.
Key ideas
Types of pathogen
Bacteria are single-celled organisms; some cause disease by releasing toxins. Viruses are far smaller and can only reproduce inside living cells, damaging them. Fungi such as athlete's foot thrive on skin, while protists such as the malaria parasite are spread by vectors like mosquitoes. Knowing the type matters because treatments differ: antibiotics kill bacteria but do nothing against viruses.
The immune response
The body's first defences are barriers: skin, mucus, and hydrochloric acid in the stomach. If pathogens get through, white blood cells called phagocytes engulf them, while lymphocytes produce specific antibodies. After the infection, memory lymphocytes remain, so a second encounter triggers a faster, stronger response — this is the basis of natural immunity.
Key term — pathogen: A microorganism that causes disease, including some bacteria, viruses, fungi and protists.
Name the four main types of pathogen and give one disease caused by each.
Bacteria – e.g. food poisoning or tuberculosis; viruses – e.g. flu or measles; fungi – e.g. athlete's foot; protists – e.g. malaria.
Answer: Bacteria – e.g. food poisoning or tuberculosis; viruses – e.g. flu or measles; fungi – e.g. athlete's foot; protists – e.g. malaria.
- Taking antibiotics for a cold or flu Colds and flu are caused by viruses, and antibiotics only kill bacteria. Using them unnecessarily also encourages antibiotic resistance.
- Thinking vaccines give you the disease Vaccines contain dead, weakened or partial pathogens that cannot cause the disease; any mild symptoms come from the immune response itself.
Practice
Antibiotics target structures and processes found in bacterial cells, such as cell walls. Viruses lack these structures and reproduce inside human cells, so antibiotics cannot attack them.
A phagocyte is a white blood cell that engulfs pathogens and digests them with enzymes, destroying the invaders.
Any two of: intact skin; mucus trapping microbes; hydrochloric acid in the stomach killing microbes; hairs and mucus in the nose.
The vaccine triggers an immune response that produces memory lymphocytes. If the real pathogen later invades, these memory cells mount a rapid response before the person becomes ill.
Quick check
Which of these best defines "pathogen"?
Give three lifestyle choices that reduce the risk of heart disease.
- Meet the Pathogens: meet bacteria, viruses, fungi and protists and find out how they make us ill.
- Types of pathogen: Bacteria are single-celled organisms; some cause disease by releasing toxins.
- antibody: A Y-shaped protein made by white blood cells that locks onto a specific antigen on a pathogen, marking it for destruction.
- Watch out for: taking antibiotics for a cold or flu