Disease, immunity, and plant biology might seem like complex topics,...
Biology331 views·Updated 17 Aug 2026·3 pagesAQA Biology: Infection and Response Notes
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fatima jawad@fatimajawad_lnfl
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Understanding Disease and Pathogens
Ever wondered why you get ill? It's all down to tiny troublemakers called pathogens - microscopic organisms that cause disease and spread easily between people, plants, and animals.
Bacteria are incredibly small cells that make you feel rough by releasing toxins that damage your body's cells. Viruses are even sneakier - they're not even proper cells! They sneak inside your cells, replicate like crazy, and cause your cells to burst, which definitely makes you feel awful.
Protists are single-celled organisms that act as parasites, living on or inside other organisms and causing damage. They often need a vector (like a mosquito) to spread from one host to another. Fungi come in different shapes and can be single cells or have thread-like structures called hyphae that penetrate skin and plant surfaces, producing spores that spread disease.
Key Insight: Pathogens spread through water, air, and direct contact - which is why washing your hands and covering coughs is so important!
Common diseases include measles (viral, spreads through coughs), HIV (viral, spreads through body fluids), tobacco mosaic virus (affects plants), and malaria (caused by protists carried by mosquitoes).
2
of 3
How Your Body Fights Back
Your body is like a fortress with multiple defence systems working 24/7 to keep pathogens out. The first line of defence includes your skin, hair, mucus glands with cilia, and stomach acid.
Your immune system is the real hero though. White blood cells patrol your body, engulfing and digesting pathogens through a process called phagocytosis. Each pathogen has a unique identifier called an antigen.
When white blood cells encounter a pathogen, they produce specific antibodies that lock onto the antigen and destroy it. These antibodies multiply rapidly, and some become memory cells that stick around in your blood. If the same pathogen tries to attack again, these memory cells recognise it immediately and mount a swift defence.
Remember: This is exactly how vaccines work - they train your immune system to recognise threats without making you properly ill!
Vaccinations have pros and cons. They control communicable diseases and prevent epidemics when lots of people get vaccinated. However, they don't always work perfectly and can sometimes cause side effects.
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of 3
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Biology331 views·Updated 17 Aug 2026·3 pagesAQA Biology: Infection and Response Notes
F
fatima jawad@fatimajawad_lnfl
Disease, immunity, and plant biology might seem like complex topics, but they're actually about how living things protect themselves and stay healthy. From understanding how your body fights off infections to learning how plants defend against threats, these concepts explain...
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Understanding Disease and Pathogens
Ever wondered why you get ill? It's all down to tiny troublemakers called pathogens - microscopic organisms that cause disease and spread easily between people, plants, and animals.
Bacteria are incredibly small cells that make you feel rough by releasing toxins that damage your body's cells. Viruses are even sneakier - they're not even proper cells! They sneak inside your cells, replicate like crazy, and cause your cells to burst, which definitely makes you feel awful.
Protists are single-celled organisms that act as parasites, living on or inside other organisms and causing damage. They often need a vector (like a mosquito) to spread from one host to another. Fungi come in different shapes and can be single cells or have thread-like structures called hyphae that penetrate skin and plant surfaces, producing spores that spread disease.
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How Your Body Fights Back
Your body is like a fortress with multiple defence systems working 24/7 to keep pathogens out. The first line of defence includes your skin, hair, mucus glands with cilia, and stomach acid.
Your immune system is the real hero though. White blood cells patrol your body, engulfing and digesting pathogens through a process called phagocytosis. Each pathogen has a unique identifier called an antigen.
When white blood cells encounter a pathogen, they produce specific antibodies that lock onto the antigen and destroy it. These antibodies multiply rapidly, and some become memory cells that stick around in your blood. If the same pathogen tries to attack again, these memory cells recognise it immediately and mount a swift defence.
Remember: This is exactly how vaccines work - they train your immune system to recognise threats without making you properly ill!
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of 3Sign up to see the content. It's free!
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