This document discusses pathogens and how they cause disease. It defines a pathogen as a microorganism like bacteria or viruses that can cause infectious disease. It describes how bacteria and viruses are structured and reproduces rapidly inside the body, with bacteria splitting and viruses taking over cells. It provides an example of Ignaz Semmelweis who realized that doctors transmitting pathogens from autopsies to patients was causing childbed fever and significantly reduced deaths by insisting on hand washing.

1. Pathogens Lesson Objectives To know the difference between viruses and bacteria. Starter Then write down a list of any diseases / illness you have had caused by pathogens.

2. SO WHAT IS A PATHOGEN? A pathogen is a disease cause by bacteria or virus. Infectious diseases are found all over the world. They are caused by a microorganism entering and attacking the body. If you can pass the microorganism on this means you are infectious. AQA Science © Nelson Thornes Ltd 2006

3. The structure of bacteria Science Photo Library/ Alfred Pasieka Cell membrane Slime capsule Cell wall Cytoplasm Genetic material Plasmids Flagella

4. The structure of a virus Science Photo Library: Kari Lounatmaa Protein coat Genetic material

5. Types of bacteria AQA Science © Nelson Thornes Ltd 2006

6. Staphylococcus aureus AQA Science © Nelson Thornes Ltd 2006 Photodisc 72(NT)/Duncan Smith

7. HOW PATHOGENS CAUSE DISEASE. Once these pathogens are inside your body they cause disease because they reproduce rapidly. Bacteria do this by splitting in two. They often produce toxins at the same time. Viruses actually take over cells, damaging and destroying them. AQA Science © Nelson Thornes Ltd 2006

8. IGNAZ SEMMELWEISS H- In the mid 1850s, many women who gave birth in hospital died from childbed fever a few days after. E- Semmelweiss realised his medical students went straight from dissecting dead bodies to delivering babies without washing their hands. AQA Science © Nelson Thornes Ltd 2006

9. IGNAZ SEMMELWEISS B - Next another doctor cut himself whislt working on a body and died from the same symptoms. He become convinced an infectious agent was causing this. I- On insisting his students washed their hands deaths significantly reduced. AQA Science © Nelson Thornes Ltd 2006

10. IGNAZ SEMMELWEISS F- However, his ideas were mocked by the medical community. Doctors did not want to believe they were causing it. In those days with no indoor plumbing and harsh chemicals washing hands was difficult. Then J and C followed by D AQA Science © Nelson Thornes Ltd 2006

11. IGNAZ SEMMELWEISS G- It is thought MRSA would be less of a problem if visitors washed their hands more. AQA Science © Nelson Thornes Ltd 2006

12. WAS HE RIGHT? AQA Science © Nelson Thornes Ltd 2006

13. Homework What was the problem with thalidomide in the 1960s?