Biology GCSE B2

Infections are caused by microogranisms entering your body and reproducing.

There are 3 types of microbes:

• virus (smallest)
• bacteria (middle)
• fungus (largest)

disease causing microogranims are called pathogens which live off their host.(parasites)

Ideal conditions for microbes:

• warmth
• moisture
• nutrients

Once bacteria invade the body they can reproduce every 20minutes 

Effects of an infection = symptoms

microogranisms enter the body --> reproduce quickly --> damage cells when reproducing or secretion of toxins --> symptoms of feeling ill 

Some bacteria produce enzymes which break down material holding cells togetherallowing them to invade more deeply.

however, microbes don't always affect us because...
- most microogranisms don't cause disease
- our bodies have physical barriers keeping them out

physical barriers:
skin-if damaged can repair itself quickly to prevent wounds gettin infected
skin openings-->sweat - forms protective layer on skin and doesnt allow growth of microbes there. 
eyes-->tears- contains enzymes that kill bacteria
stomach-->acid- hyrodchloric acid kills bacteria and stops them spreading 

 white blood cells are part of your immune system. Different types of white blood cells do different things

Phagocytes will sense a foreign microbe in the body and digest and engulf them =  phagocytosis. These also produce inflammatory responses so bloood flow to infected area increases and fluid leaks onto damaged tissue

Other white blood cells will produce antibodies :

• these can mark antigens for other WBC's 
• attach to and neutralise toxins
• attach to the antigens and kill them directly
  
  [memory cells- some white blood cells that made an antibody before remain in the blood,so if the same microbe attacks,white blood cells can produce the correct antibodies very quickly before you feel ill= immunity]. 

Colds are viruses and there are hundreds of them so its hard to become immune. Also they have a high mutation rate(change of DNA)along with the antigens on their surface, so new antibodies are made each time. 

Vaccines allow you to become immune to a disease before you actually catch it

Small amount of dead/inactive microbes injected in the body--> white blood cells recognise it and make correct antibodies --> antibodies make microbes clump together --> phagocytes digest--> memory cells remain in blood. 

mcirobes with a high mutation rate make it difficult to make vaccines for them (influenza) and some viruses like AIDS attack white blood cels so you're immune system won't work that well. 

Pros                                                               Cons
-epidemic can be prevented if large              - never completely safe, people 
% population vaccinated. even people           genetically different , so react who arent vaccinated won't catch it                        differently. 
because less passing on disease                
 - some disease can be wiped out                 -side effects may be painful

There are different opinions on vaccinations.

• some people don't want to be forced to be vaccinated
• others think the right policy is the one that leads to the best outcome for the most people
• there must be enough of the population vaccinated for a disease to be controlled

in poorer countries you are more likely to catch a disease due to crowded living conditions,poor diet, and low access to medical care. This would make it more important for them to be vaccinated. However often developing countries can't afford it so only people on the edge of a community might be vaccinated to stop it spreading outwards.