GCSE biology

HideShow resource information
Preview of Microbes

First 632 words of the document:

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 noticed that when meat rotted maggots
Why did people believe this?
­ As there was nothing else at the time that could explain why this happened as
microbes were not known
­ It was strongly supported by the church and at the time everyone was religious and
believed everything the church said.(To go against this you would have to have a lot of
However scientists changed this.. They put forward the theory of Biogenesis which was that
living things were created by other living things.
Francesco Redi conducted a test using meat ­ he put a piece of paper over meat and
covered it and left another piece of meat out in the open. The piece of meat in the open
attracted flies which laid their eggs on the meat which formed maggots whereas the covered
meat did not attract flies so no maggots grew. This ended the debate for spontaneous
generation in large things but it was still believed possible in other circumstances. (Test was
good as it could easily be reproduced and because of its simplicity.)
A scientist call Lazzaro Spallanzani then conducted a test ­ he boiled two sets of meat broth
to kill off microrganisms. He sealed off one flask to remove air from it and left the other flask
open and left them to stand for a while. No microrganisms grew in the sealed flask however
did in the open flask concluding that air is needed to provide a source of contamination.
Lazzaro concluded that the microbes got into the flask from the air and that 'fresh air'' caused
substances in food to change into microbes. (But then people argued that spontaneous
generation required air in the flask which was why nothing grew.)
Theodor Schwann then disproved Lazzaro's idea as he used sulphuric acid and heated glass
tubes to sterilise air and remove microrganisms from the air. The sterilised air was passed
through the broth in the flask and no microrganisms grew in the broth. He then exposed the
flask to normal air and microrganisms grew in the flask. He concluded that nothing would go
off in the air providing the air was heated first to kill microrganisms. (Some people argued
that boiling the air destroyed something in the air which enabled life to form.)
Louis Pasteur
Louis invented swannecked flasks. In his investigation he poured nutrient broth into the glass
flask and boiled the broth to kill any bacteria and drive out most of the air. He believed that as
the flask cooled the air would be drawn back into the flask however any bacteria in the air
would be trapped in the bend in the neck of the flask (settle in the loop) as bacteria were
considered heavier than air. He used a control experiment and boiled his broth but cut off the
long thin neck of the flask (loop) after to allow bacteria to reach the broth and microbes were
able to enter. He repeated his test. This proved that it was microbes not the air that caused
the broth to go off as the air was able to enter the flask. This provided enough evidence to
support Biogenesis and prove spontaneous generation does not occur.
Making yoghurt

Other pages in this set

Page 2

Preview of page 2

Page 3

Preview of page 3

Here's a taster:

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 > Ethanol + carbon dioxide + energy
Yeast can also respire aerobically this produces more energy than anaerobic does and the
yeast cells use spare energy for growth and respiration.…read more

Page 4

Preview of page 4

Here's a taster:

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.…read more

Page 5

Preview of page 5

Here's a taster:

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 proteins which are needed for the fungus to grow
and reproduce. The penicillium enters the growth medium inside the vessel.…read more

Page 6

Preview of page 6

Here's a taster:

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 from maize starch by the action of carbohydrase an enzyme. It is
mixed in a fermenter with yeast which uses it as an energy source to respire
anaerobically to produce ethanol and carbon dioxide.…read more

Page 7

Preview of page 7

Here's a taster:

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 a steady rate.
They have an inlet of waste to go in. An outlet for digested material to leave as fertiliser. A
outlet for biogas to leave and be piped to where it is needed.…read more

Page 8

Preview of page 8

Here's a taster:

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 to the jelly. We boil the agar jelly and then they are poured in petri
dishes and set when cold.
­ Once sterilised the dishes must be covered until required.…read more


No comments have yet been made

Similar Biology resources:

See all Biology resources »See all resources »