CBSE Class 8 Microorganisms Friend And Foe Important question and Answers

CBSE Class 8 Microorganisms Friend And Foe Important question and Answers

A.One Word Answers

1.Some microbes have a hard outer cover called :

Ans.Cyst



2.A vaccine Contains

And.Weakend or killed microbes

3.A group of similar microorganisms living together is called

Ans.Colony

4.Atmosphere comprises of 78% of

Ans.Nitrogen

5.Low temperature prevents spoilage of food because it

Ans.Retards microbial growth

6.Which bacteria is present in curd

Ans.Lactobacillus

7.The microbes used in preparation of bread is

Ans.Yeast

8.Harmful microbes are also known as

Ans.Pathogens

9.Which group of microbes contains only pathogenic members

Ans.Viruses

10.Some bacteria like E.coli living in human intestine synthesise

Ans.Vitamin b

11.The first antibiotic was prepared from

Ans.Fungus

12.When a disease causing microbes enters into our body, defense system produces

Ans.Antibodies

13.A denitrifying bacterium is

Ans.Pseudomonas

14.Which microbe is biological nitrogen fixer

Ans.Blue green algae, Rhizobium

15.The group of microorganisms where all members contain cholorophyll is

Ans.Algae

16.Louis pasteur discovered

Ans.Pasteurisation and Fermentation

17.Vaccine was discovered by

Ans.Edward Jenner B.Fill in the blanks

1.Fill in the blanks :-

a. The process of conversion of sugar into alcohol is called ______ .

b. The process of conversion of free atmospheric ni trogen into useful nitrogenous compounds is called nitrogen ______ .

c. The process of conversion of compounds of nitrog en into free molecular nitrogen is ______ .

d. Incomplete breakdown of organic matter in less a ir leading to foul smell is called______ .

e. Complete breakdown of organic matter in sufficie nt air without foul smell is called ______ .

fermentation, fixation, denitrification, putref action, decomposition .

2.Fill in the blanks :-

a. ______ are preserved by the use of oil and vineg ar.

b. ______ is the process of heat and cold treatment for preserving milk.

c. ______ is a dangerous form of food poisoning.

d. ______ is the oldest method of food preservation

. e. Jellies, squashes and jams are preserved by ____ __ syrup.

. pickles, pasteurisation, botulism, dehydration, sugar.

3.Fill in the blanks :-

a. ______ reproduce only inside the living cells.

b. ______ is a bacteria eating virus.

c. Viruses can be seen under the ______ microscope.

d. Viruses are regarded as ______ link between livi ng and non living.

e. A virus do not have ______ structure.

Virus, bacteriophage, electron, connecting, cell ular .

C.Short Answer Question answers 1.What makes the dough rise while preparing idli, dosa, bhaturas and dhoklas ?

Ans.Yeast is a beneficial fungus. Through the proces s of fermentation it breaks down sugar and produces alcohol and carbon dioxide. Bubbles of carbon dioxide gas fills the spaces in dough and make it to rise.

2. How can be communicable diseases prevented ?

Ans.one can avoid the spreading of communicable diseases :
i) we should cover our nose and mouth while we snee ze or cough.
ii) we should take care of personal and community h ygiene.
iii) we must keep food and water covered to prevent contamination.
iv) we must wash our hands before eating food .
3. What is botulism? Name the organism causing it.
Ans.When cooked food is kept for long time, some mi crobes grow on it and produces toxins over there that makes food poisonous. If suc h spoiled food is consumed it leads to food poisoning. Food poisoning caused by a bacterium named Clostrid ium botulinum is called botulism.

4.What are symbiotic or commensal bacteria and wh at is their significance for humans?

Ans. Some bacteria occur in the human intestine and intestine of other animals as well. They benefit their host and referred to as symbioti c &/or commensals like E.coli synthesizing vitamin B in our body .

5.What is an antibiotic? Give any four examples o f antibiotics.

Ans.Many microorganisms produce certain chemicals t hat inhibit the growth of some other microbes. Such chemicals are called antibioti cs. examples are penicillin, streptomycin, tetracycline, gramicidine.

6.Define pasteurization?

Ans.It is method utilised for preservation of milk. This method consists of heating milk to a high temperature of 70 0 C for about half a minute and then cooling it quic kly which kills most of the bacteria.

7.How is dehydration helpful in food preservation ?

Ans.Dehydration decreases the moisture/water conten t of food and retards the growth of food spoiling microorganisms hence helps in food pr eservation.

8.How the percentage of nitrogen in the atmosphere remain s more or less constant

Ans..Nitrogen present in air is fixed by some microbes as nitrifying bacteria. That fixed nitrogen is utilised by plants and then by animals. After th eir death, fixed nitrogen is thereafter released back into the atmosphere in its molecular form by the action of another group of microbes called denitrifying bacteria. Due to this cyclic movement the percentage of nitrogen in the atmosphere remains more or less constant

9.Differentiate between atmospheric, biological a nd industrial nitrogen fixation ?

Ans.Atmospheric nitrogen fixation takes places by el ectric discharge, during rains. Compounds of nitrogen thus formed are dissolved in rain water and reach the soil. Biological nitrogen fixation is performed by some microbes (bacteria) which convert atmospheric nitrogen into nitrogenous compounds. Industrial nitrogen fixation refers to manufacturi ng of ammonium salts and compounds in chemical factories.

10. What are chemical preservatives of food ? Name any two of them.

Ans.Food can also be preserved by the use of some c hemicals which can kill the food spoiling microorganisms. This method of conservatio n of food materials is also called as chemical preservation of food. Such chemicals th at prevent food spoilage are called food preservatives for eg. Sodium benzoate and Pota ssium metabisulphite.

11. Give one word answer to the following: i) A communicable disease caused by female anophele s mosquito.

Ans.Malaria

ii) A disease of animals and humans which is caused by bacteria.

Ans.Anthrax

12.Write 10 lines on the usefulness of microorganis ms in our lives.

Ans.The usefulness of microorganisms are as follows:

a. Lactobacillus- a bacterium useful in making curd et c.

b. Bacteria are useful in formation of bread and chees e.

c. They are used in cleaning of environment.

d. Yeasts are used in production of alcohol.

e. They are used in making antibiotics.

f. They are used in making vaccines.

g. Microorganisms are used to make manure.

h. Bacteria are main nitrogen fixing agent.

i. They fix the carbon dioxide into useful sugar.

13.Write a short paragraph on the harms caused by m icroorganisms.

Ans.The harm caused by microorganisms are as follows-

a. They cause many communicable diseases like cholera, common cold, tuberculosis etc.

b. Malaria is caused by a microorganism called plasmod ium.

c. Several plants diseases are caused by bacteria and fungi.

d. Food poisoning is caused by microorganism.

e. They are responsible for spoiling of food.

14.What are antibiotics? What precautions must be t aken while taking antibiotics?

Ans.The medicines that kill or stop the growth of the d isease-causing microorganism are called antibiotic. Streptomycin, tetracycline, eryt hromycin etc. are common antibiotics. They are manufactured by growing specific micro-org anisms and are used to cure a variety of diseases.

Following precautions must be taken in using antibi otics-

(i) These medicines should be taken only on the advice of a qualified doctor.

(ii) One must finish the course prescribed by the doctor .

(iii) If anybody takes antibiotics when not needed, his o r her body may develop resistance against that antibiotic.

15.What are the major groups of microorganisms?

Ans.The major groups of microorganisms are:- a. Bacteria

b. Fungi

c. Protozoa

d. Some algae