Summary AQA Biology A Level Revision - Cell recognition and Immune system - Unit 5
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Course
Unit 1 BIOL1 - Biology and disease (7402)
Institution
AQA
Book
AQA Biology A Level Student Book
These revision notes provide an in depth summary of this specific chapter of AQA Biology in the A Level Specification -
Very comprehensive notes and enabled me to achieve an A* in my A Level Biology exams.
Biology revision – Cell recognition and the immune system (Unit 5)
Defence mechanisms
- Any infection is an interaction between the pathogen and the body’s various defence
mechanisms
- Pathogen – a bacterium, virus or microorganism that causes disease
- Having overwhelmed the pathogen, the body’s defences seem to be better prepared
for a second infection from the same pathogen and can kill it before it causes any
harm
o This is known as immunity
Is the reason why some people aren’t affected by certain pathogens
Defence mechanisms
- Human body has numerous defences to protect itself from pathogens
- Some are general and immediate defences like skin, forming a barrier to the entry of
pathogens and phagocytosis
- Others are more specific, less rapid but longer lasting
- These responses involve a type of white blood cell called a lymphocyte
- This takes two froms
o Cell-mediated responses involving T lymphocytes
o Humoral responses involving B lymphocytes
Recognising your own cells
- To defend the body from invasion by foreign material, lymphocytes must be able to
distinguish the body’s own cells and molecules from those that are foreign
- If they couldn’t do this, lymphocytes would destroy the organism’s own tissues
- Each type of cell, self or non-self, has specific molecules on its surface – antigens
- These molecules can be of a variety of types but it’s the proteins that are the most
important – this is as proteins have a large variety and a highly specific tertiary
structure
o It is this variety of 3D structure that distinguishes one cell from another
- Its these proteins that allow immune system to identify:
o Pathogens – e.g. HIV
o Non-self material – e.g. cells from other organisms of the same species
o Toxins including those produced by certain pathogens – e.g. the bacterium that
causes cholera
o Abnormal body cells – e.g. cancer cells
- All of these are potentially harmful and their identification in the first stage is removing
the threat that they pose to organisms
o However, despite its advantages, this has implications for humans who have
had tissue or organ transplants
- The immune system recognises these as non-self even though they have come from
individuals of the same species
o Thus it attempts to destroy the transplant
To minimise the effect of this tissue rejection, donor tissues for transplant
are normally matched as closely as possible to those of the recipient
The best matches come from close relatives
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