B3 Topic 1 The Growth of Bacteria

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  • Created by: Hannah
  • Created on: 05-05-13 17:58

Most bacteria grow exponentially. Each generation doubles the size of the previous generation. Bacterial cells can divide every 20 minutes producing a new generation. Starting with a single cell, 25 cycles of division can produce more than a million descendants cells within 8-9 hours. This exponential growth can cause rapid infection. This exponential growth can only occur if the conditions are ideal. Bacteria needs: 

  • The ideal temperature
  • PH
  • Availability of resources (e.g. 02, glucose, be able to respire)

Louis Pasteur: He believed that microbes in the air caused diseases and decomposition. He carried out an experiment to prove this theory. He first heated broth in two flasks and left them open. One of the flask had a curved neck so that the bacteria in the air would settle in the loop, but not on the broth. This broth stayed fresh whilst the other one didn't. This showed that microbes cause food to go bad and that microorganisms are killed by heat. 

He then went on to invent the process called pasteurisation where you heat a substance to 70 degrees and then cooled it. This kills off most of the harmful germs. Any process which reduces contamination is called aseptic technique. This technique is used to treat raw milk to kill harmful bacteria and for it to be safe to drink. Pasteurisation is preferred to sterilising as it involves a more severe form of heat treatment. 

Sterilisation kills of everything but it changes the taste of the milk and destroys the vitamin. 

Immunisation Key Words

Immune response: the action of the lymphocytes and phagocytes when antigens infect the body. 

Antigens: any substances that stimulates the production of antibodies. 

Phagocytes: type of white blood cells that engulf viruses and bacteria destroying them. 

Lymphocytes: type of white blood cells that destroys viruses and bacteria that causes diseases. 

Antibodies: the protein normally in the body or produced in a response to an antigen which neutralises thus producing an immune result. 

Memory lymphocytes: the lymphocytes which remember the antigen of the foreign pathogen bacteria so that it can identify the virus if it enters the body again. 

Primary Immune response: response of the immune system to infection by a particular pathogen, virus or bacterium for the first time. 

Secondary Immune response: response of a immune system to subsequent infection by a pathogen that it has encountered before. 

Vaccine: a substance which contains pathogen that have been made harmless by killing it, weakening it or using only a part of it. 

Immune response: 1. Pathogens covered with a different code of antigens detected in the body. 

2. Lymphocytes and phagocytes (white blood cells) occur when the pathogens are detected. 

3. B-lymphocytes produce the protein called antibodies. The antibodies produced are specific to the pathogens and they bind to the antigens and destroy the pathogen carrying it. 

4. Phagocytes finish the job and the antibodies are the produced rapidly and flow around the body to kill all the similar bacteria or viruses. 

5. Antigens create memory lymphocytes which…


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