The k8 school logo

A Comprehensive Guide to Homeschooling

Useful micro-organisms




What is ‘sewage’?

Waste matter carried away in gutters or drains is called sewage.


What are ‘sewers’?

Waste pipes that carry away sewage are called sewers.


How do micro-organisms help to clean waste water?


1) Waste water passes through filter beds.

2) These filter beds contain sand and gravel.

3) Sand and gravel are covered by micro-organisms.

4) As waste water passes over sand and gravel in the filter beds, micro-organisms break down the waste materials quickly.

5) So the waste water can be cleaned and put into a river or a sea.





What is the fungus used to make bread?



What do tiny yeast cells do in the bread dough?

Yeast cells grow rapidly (quickly) if they have food and moisture. When they are warm and moist, the tiny yeast cells feed on the sugar which is in the bread dough and make carbon dioxide and alcohol.


What are the two waste products made by yeast cells in the bread dough?


1) Carbon dioxide gas

2) Alcohol


What does the carbon dioxide do in the bread dough?


1) The carbon dioxide makes the dough rise.

2) So that the bread is packed with little bubbles and has a light texture.


What is happening to carbon dioxide and alcohol when the bread dough is baked?

The carbon dioxide and alcohol evaporate away when the bread dough is baked.



Beer and wine


What is the fungus used to make beer and wine?




Making beer


What are used to make beer?


1) Water

2) Barley

3) Hops (A kind of a dried flower added to beer to get the bitter taste)

4) Sugar

5) Yeast


How is beer made?

Water, barley, hops and sugar are mixed. A special type of yeast is added to the mixture. And the mixture is kept warm. The yeast feeds on the sugar and makes alcohol and carbon dioxide.


What are the two waste products made by yeast in making beer?


1) Carbon dioxide gas

2) Alcohol



Making wine


What is used to make wine?

Crushed grapes


Where does the yeast that turns grape juice into wine grow?

It grows wild on the skin of the grapes.


How do these yeast cells help to make wine?

The yeast feeds on the sugar in the grape juice and produces alcohol with carbon dioxide.


What are the two waste products made by yeast in making wine?


1) Carbon dioxide gas

2) Alcohol



Cheese and yoghurt


What are used to make cheese and yoghurt?


1) Milk

2) Bacteria


How do bacteria help to make cheese and yoghurt?

The harmless bacteria are added to the boiling milk. And the milk is kept warm. Bacteria grow and multiply in warm milk by feeding on the sugar called, ‘lactose’ in the milk. Now bacteria break down lactose sugar into ‘lactic acid’. The lactic acid changes part of the milk solid or thick. Bacteria don’t eat this solid or thick part of milk and this stops any harmful bacteria growing. Some chemicals produced by the bacteria give the solid part of the milk a particular flavour.


How to get the right taste of yoghurt?

Fruit or flavouring may be added to get the right taste of yoghurt.


What is ‘Stilton?’

It is a kind of English blue cheese.


How is Stilton made?


1) A fungus or mould is added to the cheese while it is ripening.

2) This harmless fungus makes the cheese look blue and gives it a special flavour.



Other useful micro-organisms


What are the uses of other useful micro-organisms?


1) To make vinegar


2) To make antibiotics


3) To extract metals from the rocks

E.g. – The valuable metal ‘uranium’ is extracted in this way


4) To make leather

E.g. – Microbes clean the skins of dead animals before they are turned into leather


5) To clean oil tanks

E.g. – When the oil tanks on ships and in oil refineries need cleaning, some bacteria are used to feed on the waste oil of the tanks. When all the oil has been decomposed away, the tanks can then be washed out.


6) Decomposers

Inside a pile of dead leaves are millions of tiny bacteria. These bacteria feed on the leaves and break them down into nutrients. The nutrients go back into the soil where they can be used by plants.





What is an ‘antibiotic’?

A natural chemical made from a mould or bacterium that can kill microorganisms and cure bacterial infections (diseases).


What can antibiotics do?


1) They can be active against one or more bacteria.

2) They can kill bacteria.

3) They can slow down the growth of bacteria.


When were antibiotics discovered?

In 1928


Who discovered antibiotics?

A British scientist called Alexander Fleming.


What is the name of the antibiotic he discovered?



What was used to make Penicillin?

A mould called Penicillium


How was Penicillin made?

By changing the substances produced by the mould called ‘Penicillium’ into a drug.


What was the first disease cured using the antibiotic, Penicillin?

Septicemia (An infection of the bloodstream caused by micro-organisms)





What is pasteurization?

Liquids such as milk are heated until all the harmful germs are killed. This is called pasteurization. Pasteurization is one of the ways of preserving foods.


How is pasteurization done?

The liquid or milk is heated to 600C (60 degrees Celsius) and held there for at least thirty minutes and then cooled quickly. In this way all the harmful germs in the liquid can be killed.


When was pasteurization invented?

In 1864


Who invented pasteurization?

A French man named Louis Pasteur


Why is this process called pasteurization?

The process of pasteurization is named after Louis Pasteur in recognition of his great contribution to food safety.


What are the things that can be pasteurized?


Grocery items like,

1) Milk

2) Juice

3) Non-dairy milk and other similar food products.