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Triple Biology Revision Notes:
Microbes make Useful Products
Advantages of using microbes:
Minimal space required (because of contained growth)
Predictable products produced (under controlled conditions)
May be used together with a bi-product of another process to produce useful products (may
grow on waste materials from other processes)
The production of yoghurt:
Pasteurised, sterilised milk is used to avoid any unwanted microbes. When sterilised, the milk is
heated to 72oC as it kills most of the pathogenic bacteria, without compromising the taste. However,
this is not hot enough to kill food spoilage in the milk, and the food can still go off.
The milk is then mixed with specially cultured bacteria and kept to the right temperature-30o- for the
enzymes to work.
The enzymes in the bacteria ferment the sugar from the milk- lactose- into lactic acid, which gives the
sour taste and makes the product semi- solid.
The production of bread:
The production of bread involves mixing yeast, sugar and flour (made from wheat) and leaving them
somewhere warm. The bread is then kneaded to introduce oxygen for aerobic respiration. The yeast
then respires with this oxygen, producing carbon dioxide (fermentation). The carbon dioxide gas
bubbles through the dough and causes it to rise.
There are many factors which affect the rate of fermentation in yeast, including the amount of yeast,
the temperature, and the availability of glucose.
The enzymes work best in a certain temperature, therefore the temp will affect the rate of
The more yeast there is, the quicker the process of fermentation
The more glucose available, the quicker the yeast can respire, and therefore the quicker the
process of fermentation
The availability of oxygen also affects it in the same way
Biological washing powders:
Biological washing powders contain enzymes found in the digestive system:
Lipases- for breaking down fats
Proteases- for breaking down proteins
Carbohydrases- for breaking down carbohydrates.
These enzymes make it easier to remove food from clothes as they break it down (/ `digest' it).
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The production of antibiotics/ penicillin:
Penicillin is secreted by fungi, which can be grown commercially. The fungi are placed in a fermenter,
along with other nutrients, such as glucose (for respiration). The antibiotic is secreted into the
surrounding liquid and tapped off through the tube at the bottom.
Within the fermenter, yeast grows and multiplies, and at the end of their lifecycle, they produce
antibiotics which are secreted into the liquid.…read more