Class 8 Science - Chapter Microorganisms: Friend and Foe NCERT Solutions | What are antibiotics? What precautions m

What are the major groups of microorganisms?

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

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

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

Write a short paragraph on the harms caused by microorganisms.

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

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 __________.

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

Which of the following can be beaten into thin sheets?
  (a) Zinc     (b) Phosphorus     (c) Sulphur     (d) Oxygen

Fill in the blanks
(a) Most liquids that conduct electricity are solutions of , ______________ and ______________.
(b) The passage of an electric current through a solution causes ______________ effects.
(c) If you pass current through copper sulphate solution, copper gets deposited on the plate connected to the terminal of the battery.
(d) The process of depositing a layer ofany desired metal on another material by means of electricity is called .

Give two examples each of situations in which you push or pull to change the state of motion of objects.

Fill in the blanks:
(a) Friction opposes the _____________ between the surfaces in contact with each other.
(b) Friction depends on the _____________ of surfaces.                                                                                                                                                                      (c) Friction produces __________.
(d) Sprinkling of powder on the carrom board ________ friction.
(e) Sliding friction is ___________ than the static friction.

List conditions under which combustion can take place.

Indicate whether the following statements are True (T) or False (F).
(a) Unicellular organisms have one-celled body. (T/F)
(b) Muscle cells are branched. (T/F)
(c) The basic living unit of an organism is an organ. (T/F)
(d) Amoeba has irregular shape. (T/F)

Which of the following cannot be charged easily by friction?
(a) A plastic scale
(b) A copper rod
(c) An inflated balloon
(d) A woollen cloth.

Fill in the blanks:
(a) A place where animals are protected in their natural habitat is called                  .
(b) Species found only in a particular area is known as                          .
(c) Migratory birds fly to far away places because of                     changes.

Suppose you are in a dark room. Can you see objects in the room? Can you see objects outside the room. Explain.

What are the different ways in which water gets contaminated ?

How is an embryo developed?

One day Reeta went to a jeweller’s shop with her mother. Her mother gave old gold jewellery to the goldsmith to polish. Next day when they brought the jewellery back, they found that there was a slight loss in its weight. Can you suggest a reason for the loss in weight?

Define asexual reproduction. Describe two methods of asexual reproduction in animals.

Give two examples of each.
(a) Kharif crop
(b) Rabi crop

Suppose your writing desk is tilted a little. A book kept on it starts sliding down. Show the direction of frictional force acting on it.

Explain why the sliding friction is less than the static friction.

Fill in the blanks in the following :
(a) A person 1 m in front of a plane mirror seems to be _______________ m from his image.
(b) If you touch your ____________ ear with right hand in front of a plane mirror it will be seen in the mirror that your right ear is touched with ____________
(c) The size of the pupil becomes ____________ when you see in dim light.
(d) Night birds have ____________ cones than rods in their eyes..

Explain how CO₂ is able to control fires.

Fill in the blanks in the following statements:
(a) To draw water from a well we have to ——— at the rope.
(b) A charged body ———— an uncharged body towards it.
(c) To move a loaded trolley we have to ———— it.
(d) The north pole of a magnet ———— the north pole of another magnet.

Name the petroleum product used for surfacing of roads.