HARMFUL EFFECTS OF MICROORGANISMS

1. Some microorganisms are harmful to us.
2. They can cause food poisoning, food spoilage, tooth decay, illnesses or diseases.

illnesses or diseases

Tooth decay

Food poisoning

Food spoilage

USES OF MICROORGANISMS

1. Some microorganisms are very useful.
2. They are widely used in the manufacture of food and other useful 
    products in agriculture.
3. Yeast is used to make bread, tpaai, tempe and soya sauce.

bread

tempe

tapai

soya sauce

4. Some bacteria turn milk into cheese and yoghurt.

cheese

yoghurt

5. Some bacteria and fungi help to break down the remains of plants and animals
    to produce  organic fertilisers.

fertiliser

6. Microorganisms are used to produce certain antibiotics which can kill or 
    slow down the growth of bacteria that can cause certain diseases.
7. Diseases such as chickenpox, measles and mumps can be prevented 
    through vaccination. Vaccines are produced from microorganisms.

antibiotics

vaccines

8. Not all bacteris are harmful to mankind. Some bacteria cause diseases but many are useful to mankind.

MICROORGANISMS GROW

1. Microorganisms grow under suitable conditions.

2. When microorganisms grow on food, the food turns bad.
   (a) A bowl of rice will be covered with white patches after a few days.
   (b) Bread mould will grow on moist bread when the temperature is suitable.
   (c) The surface of a rotten orange is covered with patches pf fungi.

Mouldy bread

Rotten oranges

Try Your Best:

A slide of bread was left in a drawer in a kitchen. After a week, the bread was found to be mouldy. Bread mould grows best in an environment that is ____________________.

A. warm and dry
B. cold and dry
C. warm and moist
D. cold and moist


Explanation:

Bread mould is a type of fungus. Fungi grow very well in a warm and moist environment.

Answer: C

ACTIVITY (2)

Aim

To show that microorganisms move

Steps

1. Samples of water are collected from ponds, rivers or drains.
2. A dropper is used to place two drops of water sample on a glass slide. It is then covered with the slide
    cover.
3. The water sample is observed under a microscope.

Observation

A lot of tiny things are seen moving about in the water sample. Different microorganisms move in different ways.

Conclusion

Microorganisms can move.

MICROORGANISMS MOVE

1. Some microorganisms can move on their own.

2. They have special characteristics which allow them to move.

3. We can see the movements of microorganisms such as protozoa under a microscope.

The movement of Paramecium, a type of protozoa

ACTIVITY (1)

Aim
To show that microorganisms breathe

A) The effect of yeast on dough

Ingredients

1 cup of flour, 1/2 cup of warm water, 1 teaspoon of dried yeast, and 1 teaspoon of sugar

Step

1. All ingredients are mixed together to form dough.
2. The dough is then covered with a damp cloth.
3. The dough is left aside for 20 minutes.

Observation

The dough rises after 20 minutes.

At the beginning

At the end

 Conclusion

The yeast breathes, causing the dough to rise.

B) To show that yeast breathes

Aim

1. One teaspoon of sugar is mixed with some warm water in a conical flask.
2. Two teaspoons of dried yeast are then added to the mixture which is stirred with a spoon.
3. A ballon is fitted tightly over the mouth of the flask. It is then left aside in a warm place for 20 minutes.

Observation

At the beginning

After 20 minutes

1. Airbubbles can be seen forming in the flask.
2. The yeast gives off carbon dioxide which inflates the balloon.

MICROORGANISMS BREATHE

1. Like all living things, microorganisms undergo life processes.

2.Yeast is a type of fungus.

dried yeast

• Yeast looks like little round blobs under a microscope.
• Individuals are too tiny to be seen but a large cluster of them look like a white or yellow powdery substance.

3. When yeast breathes, it takes in oxygen and gives out carbon dioxide.

4. This process causes dough to rise. The air spaces in bread are the result of carbon dioxide given off when yeast acts on dough.

5. This characteristic makes yeast very important to the brewing and food making industries.