NCERT Solutions for Class 8 Science Microorganisms: Friend and Foe Chapter 2

Q 1.Fill in the blanks.
(a) Microorganisms can be seen with the help of a _____
(b) Blue-green algae fix ______ directly from the air to enhance the fertility of soil.
(c) Alcohol is produced with the help of _____
(d) Cholera is caused by ______

(a) microscope
(b) nitrogen
(c) yeast
(d) bacteria

Question 2.
Tick the correct answer.
(a) Yeast is used in the production of
(i) sugar
(ii) alcohol
(iii) hydrochloric acid
(iv) oxygen

(ii) alcohol

(b) The following is an antibiotic:
(i) sodium bicarbonate
(ii) streptomycin
(iii) alcohol
(iv) yeast

(ii) streptomycin

(c) Carrier of malaria-causing protozoan is:
(i) female Anopheles mosquito
(ii) cockroach
(iii) housefly
(iv) butterfly

(i) female Anopheles mosquito

(d) The most common carrier of communicable diseases is
(i) ant
(ii) housefly
(iii) dragonfly
(iv) spider

(ii) housefly

(e) The bread or idli dough rises because of:
(i) heat
(ii) grinding
(iii) growth of yeast cells
(iv) kneading

(iii) growth of yeast cells

(f) The process of conversion of sugar into alcohol is called
(i) nitrogen fixation
(ii) moulding
(iii) fermentation
(iv) infection

(iii) fermentation

Question 3.
Match the organisms in column A with their action in column B.

A 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 antibodies

(i) (e)
(ii) (a)
(iii) (b)
(iv) (c)
(v) (d)
(vi) (f)

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

The microorganisms cannot be seen with our naked eyes because they are very small in size. Some of these, such as fungus growing on bread, can be seen with a magnifying glass. Others cannot be seen without the help of a microscope.

Question 5.
What are the major groups of microorganisms?

Microorganisms are classified on the basis of their size into four major groups. These groups are:
(a) Bacteria
(b) Fungi
(c) Protozoa
(d) Some algae

Question 6.
Name the microorganisms which can fix atmospheric nitrogen in the soil.

Rhizobium, Clostridium and Azotobacter.

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

Microorganisms are useful to us in many ways. For example,

  • Bacteria like Lactobacillus convert milk into curd.
  • Bacteria are also involved in the making of cheese.
  • Acetobacter aceti is used for producing acetic acid from alcohol.
  • Yeast is used in the commercial production of alcohol, wine and bakery products.
  • Some specific microorganisms are helpful in manufacturing of antibiotics.
  • Microorganisms act as cleansing agents and decompose the waste products into manure.
  • Dead or weakened microbes are used in the preparation of vaccines.
  • Some bacteria fix atmospheric nitrogen and increase soil fertility.
  • Algae, yeast, fungi or bacteria may be used as an ingredient or a substitute for protein-rich foods that are suitable for human or animal consumption.
  • Some microorganisms are taken as probiotics, that are believed to provide health benefits when consumed.

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

Microorganisms are harmful to us in many ways. For example, microorganisms, called pathogens cause disease in humans, plants and animals. Pathogens or germs enter a healthy body through air, water, contaminated food and infected person by direct or indirect contact or by the carrier. Common ailments like cold, influenza (flu), cough, polio, chicken pox are caused by viruses. Foot and mouth diseases in the cattle are also caused by viruses. Typhoid, tuberculosis (TB) are caused by bacteria. Anthrax a dangerous human and cattle diseases is also caused by bacteria.

Diseases like dysentery and malaria are caused by protozoa. Ringworm is caused by fungi. Several microbes causes diseases in plants and thus reduces the yield. Citrus canker, a bacterial disease, affects trees of citrus fruit and is spread by air. Bhendi yellow vein mosaic disease is caused by a virus and is spread by insects in lady fingers. Rust of wheat is a fungal disease spread through air. Microorganisms that grow on our food sometimes produce toxic substances. These make the food poisonous causing serious illness and even death. This food-borne illness is called food poisoning.

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

Antibiotics are the medicines which kill or stop the growth of the disease-causing microbes. They are manufactured by growing specific microorganisms. They are used to cure a variety of diseases.

It is important to take antibiotic only on the advice of a qualified doctor. One must finish the course prescribed by the doctor to make the drug more effective. Antibiotics must not be taken unnecessarily because it may kill beneficial bacteria also. Antibiotics are, however, not effective against cold and flu as they are caused by viruses.

Question 10.
Name the bacteria responsible for the disease typhoid.

Salmonella typhi.

Question 11.
Chicken pox is caused by ………. virus.

Varicella-zoster.

Question 12.
………….. (disease) is caused by mycoplasma.

Pleuropneumonia.

Question 13.
Name the toxin released by T.B. bacteria.

Tuberculin toxin is released by T.B. bacteria.

Question 14.
Which microorganism is the cause of malaria?

A Protozoan, Plasmodium.

Question 15.
Write two diseases caused by bacteria.

Two diseases caused by bacteria are tuberculosis and diphtheria.

Question 16.
Name any two items that are prepared by using yeast.

Yeast is used to preparing bread and alcohol.

Question 17.

  1. Microorganisms can be seen with the help of a …………..
  2. Blue-green algae fix ………… directly from air to enhance fertility of soil.
  3. Alcohol is produced with the help of ………….
  4. Cholera is caused by ……………
  1. Microscope
  2. Nitrogen
  3. Yeast
  4. Bacteria.

Question 18.
Tick the correct answer :

  • (a) Yeast is used in the production of
    (i) sugar
    (ii) alcohol
    (iii) hydrochloric acid
    (iv) oxygen.
  • (b) The following is an antibiotic
    (i) Sodium bicarbonate
    (ii) Streptomycin
    (iii) Alcohol
    (iv) Yeast.
  • (c) Carrier of malaria-causing protozoan is
    (i) female anopheles mosquito
    (ii) cockroach
    (iii) housefly
    (iv) Butterfly.
  • (d) The most common carrier of communicable diseases is
    (i) ant
    (ii) housefly
    (iii) dragonfly
    (iv) spider.
  • (e) The bread or idli dough rises because of
    (i) heat
    (ii) grinding
    (iii) growth of yeast cells
    (iv) kneading.
  • (f) The process of conversion of sugar into alcohol is called
    (i) nitrogen fixation
    (ii) moulding
    (iii) fermentation
    (iv) infection.

(a) —> (ii)
(b) —> (ii)
(c) —> (i)
(d) —> (ii)
(e) —> (iii)
(f) —> (iii)

Question 19.
Match the organisms in Column I with their action in Column II.

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

Question 20.
Name the microorganisms which can fix atmospheric nitrogen in the soil.

Rhizobium, Clostridium md Azotobacter fix atmospheric nitrogen.

Question 21.
Can microorganisms be seen with the naked eye ? If not, how can they be seen ?

No, microorganisms cannot be seen with the naked eye. They can only be seen with the help of microscope.

Question 22.
What are the major groups of microorganisms ?

  • Bacteria
  • Fungi
  • Protozoa
  • Algae.

Question 23.
What are microorganisms ?

Microorganisms are organisms that are so small that they can only be seen through a microscope.

Question 24.
Name two diseases caused by viruses.

Influenza and cough.

Question 25.
Name two diseases caused by protozoans.

Dysentery and malaria.

Question 26.
Which microorganisms are unicellular ?

Bacteria and protozoa are unicellular.

Question 27.
Name two multicellular microorganisms.

Algae and fungi are multicellular.

Question 28.
Name the bacterium used for production of acetic acid from alcohol.

Acetobacter aceti.

Question 29.
Define fermentation.

The process of conversion of sugar into alcohol is called fermentation.

Question 30.
Why antibiotics are not effective against cold and flu ?

Cold and flu are caused by viruses, so the antibiotics are not effective against them.

Question 31.
What are antibodies ?

When a disease carrying microbe enters our body, the body produces antibodies to fight the invader.

Question 32.
Name two diseases which can be prevented by vaccination.

Cholera and tuberculosis can be prevented by vaccination.

Question 33.
Name the diseases for which oral drops are given as vaccination.

Polio.

Question 34.
What are biological nitrogen fixers ?

Some bacteria and blue-green algae are able to fix nitrogen from the atmosphere to enrich soil with nitrogen and increase fertility, are known as biological nitrogen fixers.

Question 35.
What are pathogens ?

Diseases-causing microorganisms are called pathogens.

Question 36.
What are communicable diseases ?

Microbial diseases which can spread from an infected person to a healthy person through air, water, food or physical contact are known as communicable diseases.

Question 37.
Name two communicable diseases.

Chicken pox and tuberculosis.

Question 39.
Name two carriers of disease-causing microbes.

Housefly and female Anopheles mosquito.

Question 40.
Name the causative microorganism of tuberculosis and its mode of transmission.

Causative microorganisms – Bacteria.
Mode of transmission – Air.

Question 41.
How are cholera and typhoid transmitted ?

Cholera is transmitted through water or food.
Typhoid is transmitted through water.

Question 42.
Which microorganism causes foot and mouth disease of cattle ?

Virus.

Question 43.
Name one plant disease caused by bacteria and its mode of transmission.

Citrus canker is caused by bacteria and transmitted through air

Question 44.
Name one plant disease transmitted by insects and caused by virus.

Yellow vein mosaic of bhindi.

Question 45.
Name one plant disease caused by fungi and its mode of transmission.

Rust of wheat. It is transmitted through air and seeds.

Question 46.
What is meant by food poisoning ?

Food poisoning is caused by consuming food that has bean spoilt by some microorganisms.

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