B2 Biology Gcse Revision

Only available on StudyMode
  • Download(s) : 83
  • Published : May 28, 2013
Open Document
Text Preview
Microorganisms:
* Small living organisms; there are 3 types
* Bacteria – ecoli, salmonella
* Fungi – mushrooms, athletes foot
* Virus – influenza (flu), HIV
* When they enter our body, they multiply and release toxins / harmful chemicals into our blood * They duplicate every 20 minutes
* Physical barriers: eyelashes prevent MO’s from entering through our eyes, nasal hairs reduce them, skin is a barrier to them (although they can enter through cuts), chemicals in tears and sweat, acid in the stomach kills most MO’s * Also called pathogens (microorganisms that cause disease) * Our body provides MO’s with ideal conditions to multiply in (warm and moist) The immune system:

* All white blood cells are part of this system
* Phagocyte – a type of white blood cell that will eliminate the virus by engulfing then digesting the bacteria, the process of this is called phagocytosis. * Lymphocyte – a type of white blood cell that carry antibodies * Antigen – certain chemicals that are foreign to the body in pathogens * E.g.:

1. James is infected by some bacteria that cause a disease. 2. The bacteria reproduce and produce toxins that make James ill 3. A white blood cell detects the bacteria and it makes antibodies to attach to it. Other white blood cells engulf the labelled bacteria and destroy them 4. The white blood cells that produce the right antibodies reproduce meaning there are lots of them making antibodies 5. Most of the white blood cells that make this antibody die, but there are few that stay in the blood called memory cells 6. The bacteria are killed and James gets better

7. He is then infected by the same bacteria
8. The memory cells that stayed in James’ blood from last time respond quickly and kill the bacteria before he becomes ill * Memory cell – a type of white blood cell that stay in the blood after the infection has been fought off * They respond quickly when it meets a microorganism for the second time and produce the right antibody for the particular microorganism and destroy it before you feel unwell meaning you become immune to a disease. Vaccinations:

* Vaccination involves exposing the body’s immune system to a dead or inactive version of the pathogen in order to stimulate white blood cells to produce antibodies for a disease or group of diseases * People can be immunised against a pathogen through vaccination. Different vaccines are needed for different pathogens * The vaccine contains only a weakened or harmless version of a pathogen, which means that the vaccinated person is in no danger of developing the disease * Epidemic – a widespread occurrence of an infectious disease in a community at a particular time * To prevent epidemics a large percentage of the population needs to be vaccinated Antimicrobials:

* Chemicals that inhibit the growth of MO’s or kill them, but don’t kill viruses * Antibiotics – type of antimicrobial that kill bacteria but don’t kill viruses * MO’s can sometimes become resistant to antimicrobials (leads to a gene for resistance being passed down to offspring) * Antibiotic resistance – when some of the bacteria are resistant to the antibiotics, this can be slowed down by finishing the course and only taking them when needed * The main steps in the development of resistance are:

1. Random changes or mutations occur in the genes of individual bacterial cells 2. Some mutations protect the bacterial cell from the effects of the antibiotic 3. Bacteria without the mutation die or cannot reproduce with the antibiotic present 4. The resistant bacteria are able to reproduce with less competition from normal bacterial strains * Mutations in bacteria can result in them becoming resistant to antibiotics, turning the bacteria into a ‘superbug’ * MRSA is a superbug resistant to almost all antibiotics

Clinical trials:
* When a new drug is tested on humans to find...
tracking img