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Theory of Biogenesis

A hypothesis is an idea to explain observations
People used to think that life could could spontaneously generate (just appear) from nonliving
material. For example when food goes bad it was caused by the food. e.g. people thought
that maggots were created by meat rotting as they…

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A fermentation process is used to make yoghurt. Milk contains lactose sugar some
bacteria will ferment lactose to produce lactic acid.

Milk is heat treated (pasteurised) to kill off any bacteria that may be present. The milk is then
cooled to around 40 degrees so the bacteria can work at…

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Yeast is a singlecelled fungus. It reproduces by asexual budding which is splitting up into two
new yeast cells. It has a nucleus,cytoplasm, a vacuole, a cell membrane surrounded by cell

Yeast can respire without oxygen (anaerobically). The process of anaerobic respiration in
yeast is called fermentation.
Glucose >…

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Microorganisms can be grown in large vessels called fermenters. Industrial fermenters
contains a liquid culture medium which the microorganisms can grow and reproduce in. The
fermenter needs to give the microorganism the conditions/ideal environment they need to
grow and reproduce their useful product in.

Industrial fermenters have:
­ An…

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Penicillin is made by growing the mould penicillium in a fermenter. Penicillium is a fungus. It is
grown in a growth medium containing glucose and nitrogen.

Glucose is needed by Penicillium to respire to produce energy to reproduce. Nitrogen source
is need (NH4) as it builds amino acids into…

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Fuels can be made by fermentation of natural products. Fermentation is when yeast break
down sugars (glucose) by anaerobic respiration to produce ethanol.

Glucose > Ethanol + carbon dioxide + energy

Ethanol based fuels can be made by the anaerobic fermentation of
­ Sugar cane juices
­ Glucose derived…

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Batch generators which make biogas in small batches. They are manually loaded with waste
material which is left to ferment/digest and the by products are cleared away at the end of
each session.

Continuous generators make biogas all the time. Waste is continually fed in and biogas is
produced at…

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Bacteria and microorganisms cannot make their own food ­ they need a food supply to
grow. The food should contain an energy source usually a carbohydrate with proteins, mineral
ions and vitamins. In a laboratory microorganisms are grown on agar jelly which contains
these nutrients.

­ Nutrients are added…


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