Biology unit 3

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Microbiology - study of tiny organisms which you need a microscope to see them.

The 3 main types of mircobes:

  • Bacteria - single celled, smaller than animal/plant cells. Harmful and helpful
  • viruses - smaller than bacteria, not alive, take over cells, cause disease
  • fungi - larger than bacteria, include yeasts and moulds

theory of bio-genesis

living things can only be created from other living things 

Spananazani (1765), Schwann (1837), Pasteur (1859) all provide evidence to support this theory, prove that life could not spontaneously generate

Culturing Microbes

Microbes -> grown/cultured in either broth or nutrient agor (generally poured into petri dishes)

growing microbes -> materials sterilized -> prevent contamination

Microbes from the air must be prevented from entering the dishes.  

This can be done by:

  • flaming the loops and necks of bottles
  • swab desks with disinfectant
  • agar is made in sterile conditions
  • dishes are sterilized before disposal
  • only incubate dishes at 25 degrees to prevent microbes growing too much and the growth of ones pathogenic to humans

They must be provided with food, can't make their own. Require carbohydrates as an energy source and also minerals (phosphates) 


used in bread making, beer and wine. It is a fungus respires in two ways:

- Aerobic respiration: 

glucose + oxygen -> carbon dioxide + water + energy

this gives lots of energy for growth

- anaerobic respiration: 

glucose -> ethanol + carbon dioxide + energy (small amount)

How yeast is used to make bread

  • mix flour, sugar, water and yeast
  • leave in warm place to grow, makes Co2, dough rises
  • bake bread - kills yeast, gas expands, bread rises further

how yeast is used to make beer

  • soak barley grains in water, keep them warm
  • extract sugary solution - malting 
  • use as energy source for yeast
  • yeast and sugary solution is fermented
  • produces alcohol
  • leave to clear and develop its


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