Thursday, 18 February 2016

TEXTBOOK ANSWERS AND SOLUTIONS OF CBSE CLASS VIII SCIENCE Chapter 2 MICROORGANISMS FRIEND AND FOE







Exercise

Fill in the blanks
(a) Microorganisms can be seen with the help of a _ microscope _.
(b) Blue green algae fix __nitrogen _ directly from air to enhance fertility of soil.
(c) Alcohol is produced with the help of _ yeast_.
(d) Cholera is caused by _ bacteria_.

2) Tick the correct answer

(a) Yeast is used in the production of
(i) Sugar
(ii) Alcohol
(iii) Hydrochloric acid
(iv) Oxygen

ANSWER- i) sugar

(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 cells
(iv) kneading

ANSWER:-(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

ANSWER:-iii) fermentation

3) 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 choler
(vi) A virus                                f) Causing AIDS
   (g) Producing antibodies



ANSWER:-
i---------e
ii---------a
iii---------b
iv---------c
v-----------d
vi----------f

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

ANSWER:-Micro-organisms are too small to be seen through naked eyes. They can be seen with the help of a magnifying glass or microscope.

5) What are the major groups of microorganisms?



ANSWER:-There are five major groups of micro-organisms:

(i) Bacteria − They are single celled disease -causing micro-organisms. They can be spiral or rod- shaped.

(ii) Fungi − They are mostly multicellular disease-causing microbes. Bread moulds are common examples of fungi.

(iii) Protozoa − They mainly include organisms such as Amoeba, Plasmodium,etc. They can be unicellular ormulticellular.

(iv) Virus −Viruses are disease-causing microbes that reproduce only inside the host organism.

(v) Algae − They include multicellular, photosynthetic organisms such as Spirogyra, Chlamydomonas, etc.

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

ANSWER:-Bacteria such as Rhizobium and certain blue- green algae present in the soil can fix atmospheric nitrogen

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

ANSWER: -Importance of micro-organisms:

Lactobacillus is used to form curd from milk.

Rhizobiums present in the roots of pulse plants fix nitrogen from air and supply nitrogen compounds to the pulse plants. They are used in winemaking, baking, pickling, and other food making processes.

Microbes also play an important role in the preparation of medicines. Antibiotics are chemicals produced by micro-organisms to kill bacteria.

Alcoholic fermentation by yeast is widely used in the preparation of wine and bread.

Bacteria present in our intestine helps in proper digestion and release Vitamin B which is absorbed by intestine.

Yeast is used in making idlis, bread, pastries and cakes.

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

ANSWER:-Micro-organisms cause diseases in animals. For example, in humans, bacteria cause diseases such as tuberculosis, cholera, typhoid, etc. In cattle, the foot and mouth disease is caused by a virus. Also, several microbes cause diseases in plants. For example, the productivity of wheat, orange, apple, etc. is reduced due to microbial diseases in plants. Certain microbes, on entering into our body, produce toxic substances. This leads to food poisoning. Some micro- organisms such as fungus spoil our food.

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

ANSWER:-Antibiotics are medicines produced by certain micro- organisms to kill other disease-causing micro- organisms.

Precautions to be taken while using antibiotics:
(i) Antibiotics should be taken under the supervision of a well qualified doctor.
(ii) Course (intake) of antibiotics should be completed as per the prescription given by the doctor.
(iii) Antibiotics should be taken in the right amount and at the right time. A wrong dose of antibiotics makes the drug ineffective. Also, excessive consumption of drugs may kill the useful bacteria present in our body.




Written By Badal Paul
The author is a passionate blogger, writer and educationalist. This blog is created to ease troubles of the Cbse students. The author holds multiple blogs and the writer of the Novel KALCHAKRA, OOM AND THE CHOSEN FIVE.