How Pathogens Cause Disease Revision Notes | GCSE OCR Foundation Biology

What this lesson covers

Explore how bacteria and viruses reproduce rapidly in the body, how bacteria produce toxins that damage tissues, and how viruses live inside cells causi...

• Explain how bacteria and viruses reproduce rapidly inside the human body
• Describe how bacterial toxins damage tissues and cause illness symptoms
• Compare how bacteria and viruses cause disease through different mechanisms
• Evaluate the relative dangers of bacterial and viral infections

Key ideas to keep in view

Use this lesson to stay inside B6.3 Monitoring and maintaining health while connecting the detail back to the wider B6: Global challenges topic.

• B6: Global challenges
• B6.3 Monitoring and maintaining health
• GCSE OCR Foundation Biology

Lesson notes preview

Read the core explanations from How Pathogens Cause Disease before testing yourself from memory.

• You wake up with a sore throat, fever, and feel terrible. But what's actually happening inside your body? The culprits are pathogens - microscopic invaders that have found their way into your system and are now causing chaos.
• There are two main types of pathogens that make us ill: bacteria and viruses. They might both be tiny, but they cause disease in completely different ways. Understanding these differences is crucial for your exams and explains why some illnesses need antibiotics while others don't.
• A microorganism that causes disease in living organisms. Examples include bacteria, viruses, fungi and protists.
• Picture bacteria as tiny factories that have invaded your body. Once inside, they don't just sit there - they get to work immediately. Bacteria reproduce rapidly by binary fission, doubling their numbers every 20-30 minutes under ideal conditions.
• Here's where it gets nasty. Many bacteria produce toxins - poisonous chemicals that damage your tissues directly. These toxins are like molecular weapons that attack your cells, causing the symptoms you feel when you're ill.
• A poisonous substance produced by bacteria that damages tissues and causes illness symptoms.
• Trap: Many students think bacteria directly attack cells like viruses do. Actually, most bacterial damage comes from the toxins they release, not from the bacteria themselves destroying cells.
• This exponential growth explains why bacterial infections can make you feel ill so quickly. The toxins from millions of bacteria overwhelm your immune system.
• Viruses work completely differently from bacteria. Think of a virus as a microscopic pirate that hijacks your cells. Viruses cannot reproduce on their own - they need to get inside your cells and use your cellular machinery.
• Once inside a host cell, the virus takes control. It forces the cell to make copies of the virus instead of doing its normal job. This process damages or destroys the host cell, and when the cell bursts open, hundreds of new viruses are released to infect more cells.

Continue through the topic

Move to the related lessons or back to the topic page when you need the wider sequence before exam-style practice.