Contains the full lesson along with a supporting toolkit, including teachers’ notes.
Why do we need a defence system?
This lesson looks at the defence system in humans. In particular, it covers the general and specific mechanisms the body uses to overcome attack from disease-causing agents. We also learn how we can use vaccines to strengthen our immune system against particular diseases.
Our bodies are a rich resource of materials that other organismscould use to grow and reproduce. We are constantly under attack from a wide variety of organisms that try to ‘feed on’ us.
Our greatest enemies are the pathogenic bacteria, viruses,fungi and protista. For example, malaria, our most lethal enemy, is caused by a unicellular protist and infects half a billion new people each year killing almost 3 million.
We also have to protect ourselves from our own rogue cells -cancerous cells.
How do we protect ourselves?
Our bodies have two major defence strategies – general and specific.
The general defence system is made up of components that deal with all pathogens in the same manner. The main general defence strategies are: barrier defence, phagocytosis, feverand inflammation, interferon and the complement system.
In contrast, the specific defence system can distinguish between different pathogens. It attacks each pathogen with a unique antibody produced in enormous quantities by a particular clone of B-cells.
How do we stop pathogens from entering the body?
Our skin is our major defence barrier against pathogens trying to enter our bodies. Skin protects us with its impenetrable outer layer of dead cells, the bactericides and fungicides in sweat andsebum, protective enzymes and mutualistic bacteria and yeast living on the surface. If the skin tears, blood clotting will quickly seal the break to help keep pathogens out.