Lesson: Microorganisms: Friend and Foe
Exercise:

# Question: 1

Fill in the blanks :
(a) Microorganisms can be seen with the help of a _________.
(b) Blue green algae fix _________ directly from air to enhance fertility of soil.
(c) Alcohol is produced with the help of _________.
(d) Cholera is caused by _________.

## Solution:

(a) Microorganisms can be seen with the help of a microscope.
(b) Blue green algae fix nitrogen directly from air to enhance fertility of soil.
(c) Alcohol is produced with the help of yeast.
(d) Cholera is caused by pathogenic bacteria.

# Question: 2

Yeast is used in the production of

(a) Sugar

(b) Alcohol

(c) Hydrochloric acid

(d) Oxygen

b

# Question: 3

The following is an antibiotic
(a) Sodium bicarbonate
(b) Streptomycin
(c) Alcohol
(d) Yeast

b

# Question: 4

Carrier of malaria-causing protozoan is:
(a) Female Anopheles mosquito
(b) Cockroach
(c) Housefly
(d) Butterfly

a

# Question: 5

The most common carrier of communicable diseases is
(a) Ant
(b) Housefly
(c) Dragonfly
(d) Spider

b

# Question: 6

The bread or idli dough rises because of
(a) Heat
(b) Grinding
(c) Growth of yeast cells

c

# Question: 7

The process of conversion of sugar into alcohol is called
(a) Nitrogen fixation
(b) Moulding
(c) Fermentation
(d) Infection

c

# Question: 8

Match the organisms in Column I with their action in Column II.

 Column I Column II (i) Bacteria (a) Fixing nitrogen (ii) Rhizobium (b) Setting of curd (iii) Lactobacillus (c) Baking of bread (iv) Yeast (d) Causing malaria (v) A protozoan (e) Causing cholera (vi) A virus (f) Causing AIDS (g) Producing antibodies

## Solution:

 Column I Column II (i) Bacteria (e) Causing cholera (ii) Rhizobium (a) Fixing nitrogen (iii) Lactobacillus (b) Setting of curd (iv) Yeast (c) Baking of bread (v) A protozoan (d) Causing malaria (vi) A virus (f) Causing AIDS

# Question: 9

Can microorganisms be seen with the naked eye? If not, how can they be seen?

## Solution:

Microorganisms are single-celled organisms, hence too small to be seen with the naked eye. They can only be seen with the help of a magnifying glass or under a microscope.

# Question: 10

What are the major groups of microorganisms?

## Solution:

There are five major groups of micro-organisms:

1.      Bacteria $–$ These are single-celled micro-organisms. They can be spiral, rod- shaped, spherical or comma-shaped.

2.      Fungi $–$ These are mostly multi cellular microbes. Bread moulds and yeasts are common examples of fungi.

3.      Protozoa - These can be unicellular or multi cellular in nature and live as predators or parasites. Amoeba, plasmodium are some examples of protozoa.

4.      Viruses - Viruses are disease-causing microbes that reproduce only inside the host organism.

5.      Algae - These include multi cellular, photosynthetic organisms, such as, Spirogyra, Chlamydomonas, etc.

# Question: 11

Name the microorganisms which can fix atmospheric nitrogen in the soil.

## Solution:

Bacteria, such as Rhizobium and certain blue-green algae can fix atmospheric nitrogen in the soil and help to increase the fertility of the soil. They are commonly called biological nitrogen fixers.

# Question: 12

Write 10 lines on the usefulness of microorganisms in our lives.

## Solution:

Micro-organisms are small and cannot be seen through naked eyes. However, they are vital to plants and the environment.

The bacterium Lactobacillus is used to form curd from milk.
Microorganisms, like Rhizobium and blue green algae are of great importance in agriculture. They increase soil fertility by fixing atmospheric nitrogen and converting it into nitrogenous compounds that are required by the plants.

Micro-organisms are also used in winemaking, baking, pickling, and other food making processes.

Alcoholic fermentation by yeast is widely used in the preparation of wine, bread, and cakes. Some microorganisms decompose organic waste, and dead plants and animals into simple inorganic substances, and this way, clean up the environment.
Bacteria are also used for the production of antibiotic medicines like penicillin, streptomycin, tetracycline and erythromycin.

Bacteria present in our intestines help in proper digestion of food and help to release Vitamin B, which is easily absorbed by our intestines. Many vaccines are prepared from micro-organisms. These vaccines are given to children to protect them from diseases.

The algae are used as food for some breeds of fish. Certain microbes are also used in the biological treatment of sewage and industrial effluents.

# Question: 13

Write a short paragraph on the harm caused by microorganisms.

## Solution:

At times micro-organisms cause diseases in human beings, plants and animals. For example, in humans, bacteria cause diseases such as tuberculosis, cholera, typhoid, etc.  The foot and mouth disease in cattle, common cold and chicken pox are caused by viruses.

Several microbes cause diseases in plants such as wheat, orange, rice, apple, sugarcane, etc.

When certain microbes enter our body, these produce toxic substances which sometimes lead to food poisoning. Micro-organisms, like fungus, spoil our food. For example, if we keep unused bread in moist condition, it will get infected by fungus, which produces toxic substances and can cause illness if we consume that infected bread.

# Question: 14

What are antibiotics? What precautions must be taken while taking antibiotics?

## Solution:

The powerful medicines made from certain micro-organisms that are used for the treatment of bacterial infection, which kill or stop the bacterial growth are called antibiotics.

Antibiotic medicines like streptomycin, tetracycline and erythromycin are commercially produced from bacteria and fungi.
Precautions to be taken while taking antibiotics:

·         Antibiotics must always be taken on the advice of a qualified doctor.

·         Course (intake) of antibiotics must be completed as per the doctor’s prescription

·         It is important to take antibiotics in the right amount and at the right time. A wrong dose of antibiotics can sometimes make the drug ineffective. Also, excessive consumption might kill the useful bacteria that are needed by our body. It might also result in the bacteria becoming resistant, rendering the antibiotic to be less effective against it.