Microorganisms: Friend and Foe - 8th science

Question (1) Fill in the blanks:

(a) Microorganisms can be seen with the help of a __________.

Answer: Microorganisms can be seen with the help of a microscope.

(b) Blue green algae fix _________ directly from air to enhance fertility of soil.

Answer: Blue green algae fix nitrogen directly from air to enhance fertility of soil.

(c) Alcohol is produced with the help of ________.

Answer: Alcohol is produced with the help of microorganisms called yeast.

(d) Cholera is caused by ______.

Answer: Cholera is caused by bacteria.

Question (2) Tick the correct answer:

(a) Yeast is used in the production of

(i) Sugar

(ii) Alcohol

(iii) Hydrochloric acid

(iv) Oxygen

Answer: (ii) Alchohol

(b) The following is an antibiotic

(i) Sodium bicarbonate

(ii) Streptomycin

(iii) Alcohol

(iv) Yeast

Answer: (ii) Streptomycin

(c) Carrier of malaria causing protozoan is

(i) Female Anopheles mosquito

(ii) Cockroach

(iii) Housefly

(iv) Butterfly

Answer: (i) Female Anopheles mosquito

(d) The most common carrier of communicable diseases is

(i) Ant

(ii) Housefly

(iii) Dragonfly

(iv) Spider

Answer: (ii) Housefly

(e) The bread or idli dough rises because of

(i) heat

(ii) grinding

(iii) growth of yeast cell

(iv) kneading

Answer: (iii) growth of yeast cell

(f) The process of conversion of sugar into alcohol is called

(i) Nitrogen fixation

(ii) Moulding

(iii) Fermetation

(iv) Infection

Answer: (iii) Fermemtation

Question (3) Match the Column A with their action in Column B

Column A	Column B
(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 antibiotics

Answer

Column A	Column B
(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	(g) Producing antibiotics (f) Causing AIDS

Question (4) Can microorganisms be seen with the naked eye? If not, how can they be seen?

Answer: No. Microorganisms can be seen using a microscope.

Explanation: (a) Since microorganisms cannot be seen without a microscope, thus it is one of the causes that they are called microorganisms.

(b) Microorganisms are so micro that they cannot be seen by naked eyes that's why they are called microorganisms. Microorganisms can be seen only using a microscope.

Question (5) What are the major groups of microorganisms?

Answer: There are four major groups of microorganisms, these are bacteria, fungi, protozoa and some algae. Apart from these virus is also microorganisms.

Questions (6) Name the microorganisms which can fix atmospheric nitrogen in the soil.

Answer: Some microorganisms such as Rhizobium and some algae fix atmospheric nitrogen in the soil.

Question (7) Write 10 lines on the usefulness of microorganisms in our lives.

Answer: Many microorganisms are very useful for us.

A bacterium named Lactobacillus is used to convert milk into curd.

A bacterium called yeast is used to convert sugar into alcohol. Yeast is used to make the dough for making of bread and cake. The process of conversion of sugar into alcohol is called fermentation.

Viruses are used to produce antibodies which are used in vaccination. These antibodies enable us to keep healthy while attacking of virus.

Some microorganisms, such as fungi decomposes dead animals and plants and mix them into soil. By decomposing dead animals and plants microorganisms help to keep environment clean.

Some microorganisms, such as Rhizobium which is a bacteria and some algae absorb nitrogen from environment and make nitrogen in the soil in soluble form. This soluble form of nitrogen is absorbed by plants from soil. By this way microorganisms increase the fertility of soil.

Some microorganisms are used as vaccine. These microorganisms after entering in our body prepare antibodies which keep us healthy while attacking by diseases causing virus.

Microorganisms which are useful to us are generally referred as friendly microorganisms.

Question (8) Write a short paragraph on the harms caused by microorganisms.

Answer: There are many microorganisms are harmful for us. These harmful microorganisms are responsible for many diseases in animals and plants. Some microorganisms spoil food and even clothes and articles made of leather.

Diseases causing such microorganisms are known as pathogens also.

TB, cholera, typhoid, flu, etc. are some examples of diseases caused because of microorganisms. Diseases like chicken pox, small pox, hepatitis A, etc. are caused by microorganisms called virus. Malaria is a deadly disease caused by microorganism called protozoa.

Question (9) What are antibiotics? What precautions must be taken while taking antibiotics?

Answer: Medicines prepare with the help of microorganisms called bacteria are called antibiotics. Antibiotics act against disease causing bacteria, stop their growth and destroy them. Antibiotics are available in the form of tablets, syrup and injections. Antibiotics are given to sick people according to need by doctors.

Precaution while taking Antibiotics

(a) Antibiotics should not be taken without the advice of a qualified doctor.

(b) One should must complete the prescribed course of antibiotics.

(c) Antibiotics must not be taken unnecessarily, otherwise it may kill the useful bacteria of the body.