Class 8 Science - Chapter Microorganisms: Friend and Foe NCERT Solutions | Name the microorganisms which can fix at

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

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

What are the major groups of microorganisms?

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.

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 __________.

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

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 ?

Indicate whether the following statements are True (T) or False (F):
(a) Oviparous animals give birth to young ones.                                    ( )
(b) Each sperm is a single cell.                                                              ( )
(c) External fertilization takes place in frog.                                           ( )
(d) A new human individual develops from a cell called gamete.          ( )
(e) Egg laid after fertilization is made up of a single cell.                       ( )
(f) Amoeba reproduces by budding.                                                       ( )
(g) Fertilization is necessary even in asexual reproduction.                  ( )
(h) Binary fission is a method of asexual reproduction.                         ( )
(i) A zygote is formed as a result of fertilization.                                    ( )
(j) An embryo is made up of a single cell.                                              ( )

Explain why some fibres are called synthetic.

Give examples to show that plastics are noncorrosive in nature.

(a) Find out the position of the image of an object situated at A in the plane mirror (Fig. 16.21).
(b) Can Paheli at B see this image?
(c) Can Boojho at C see this image?
(d) When Paheli moves from B to C, where does the image of A move?

Boojho made the following sketch (Fig. 17.29) of the solar system. Is the sketch correct? If not, correct it.

Boojho stands at A just on the side of a plane mirror as shown in Fig. 16.20. Can he see himself in the mirror? Also can he see the image of objects situated at P, Q and R?

The radius of Jupiter is 11 times the radius of the Earth. Calculate the ratio of the volumes of Jupiter and the Earth. How many Earths can Jupiter accomodate?

Two mirrors meet at right angles. A ray of light is incident on one at an angle of 30° as shown in Fig. 16.19. Draw the reflected ray from the second mirror.

Why is the distance between stars expressed in light years? What do you understand by the statement that a star is eight light years away from the Earth?

How many images of a candle will be formed if it is placed between two parallel plane mirrors separated by 40 cm?