Class VIII, Microorganisms: Friends and Foe
Solutions of Ncert (Cbse) Science Textbook Exercise
Question.1: 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 _______.
Answer: (a)
microscope (b) atmospheric oxygen (c) yeast (d) bacteria.
Question.2: Tick the correct answer:
Answer: (a)
ii (b) ii (c) i (d) ii (e) iii (f) iii.
Question.3: Match the organisms in column I with their actions
in column II:
Column I
|
Column II
|
(i)
Bacteria
(ii)
Rhizobium
(iii)
Lactobacillus
(iv)
Yeast
(v)
A protozoan
(vi)
A virus
|
a)
Nitrogen fixation
b)
Setting of curd
c)
Baking of bread
d)
Causes Malaria
e)
Causing Cholera
f)
Causing AIDS
g)
Producing antibodies
|
Answer: (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?
Answer: No,
microorganisms can not be seen with naked eyes. They are so small that they can
not be seen with naked eyes. A microscope is required to see these organisms.
Question.5: What are the major groups of microorganisms?
Answer: Microorganisms
are mainly divided into five groups - Bacteria, Fungi, Protozoa, Algae and
Virus.
Question.6: Name the microorganisms which can fix atmospheric
nitrogen in the soil.
Answer: Certain
type of bacteria and blue green algae fix atmospheric nitrogen. For example
Bacteria like- Rhizobium, Azotobacter and blue green algae like- Anabaena,
Nostoc.
Question.7: Write ten lines on the usefulness of microorganisms
in our lives.
Answer: Microorganisms
are very useful to us. Some of their usefulness is as follows:
1.
They
are used in the preparation of curd, bread and cake. Lactobacillus promotes the
formation of curd and Yeast in the baking industry.
2.
Commercially
microorganisms are used for the large scale production of alcohol, wine and
vinegar.
3.
Yeast
is used for commercial production of alcohol and wine while, Acetobacter
bacteria cause conversion of alcohol to vinegar.
4.
In
medical industry antibiotics are made from microorganisms like - some fungi and
bacteria.
5.
Microorganisms
are also used to prepare vaccines for various diseases.
6.
Microorganisms
(bacteria) help us in cleaning of our environment as they decompose the dead
bodies of plants and animals and other organic wastes.
7.
In
agriculture, microorganisms are used to increase soil fertility by fixing
nitrogen.
8.
Some
bacteria like - Rhizobium and some blue green algae are able to fix nitrogen
from the atmosphere to enrich soil and thus increase its fertility.
9.
It
is due to the activities of microorganisms because of which we are able to
prepare manure by decomposing organic wastes and dead bodies of plants and
animals.
10. In food industry, they are used as
preservatives for food items. Further, some fungi are eaten raw as food such
as, Mushrooms.
Question.8: Write a short paragraph on the harms caused by
microorganisms.
Answer: Microorganisms
can be very harmful to us, as they cause a number of human and animal diseases.
Diseases in humans like common cold, tuberculosis, measles, chicken pox, polio,
cholera, typhoid, hepatitis-B, malaria etc. all are caused by microorganisms.
Some serious diseases like- Anthrax is a dangerous human and cattle disease
caused by a bacterium. Microbes grow on food products and render them unfit for
consumption. Consumption of such food causes food poisoning. Microbes also
spoil clothes and leather products. Microorganisms cause diseases of plants
like - blights in potatoes, sugarcanes, oranges then, rust of wheat citrus,
canker etc. They also reduce the crop yield.
Question.9: What are antibiotics? What precautions must be taken
while taking antibiotics?
Answer: Medicines
taken to kill or stop the growth of harmful or disease causing microbes in
human body are called antibiotics. Antibiotics are very useful as only
antibiotics can save us from many microbial infections and diseases.
Antibiotics are made from fungi and bacteria. Alexander Fleming discovered the
first antibiotic called Penicillin in 1929. Now-a-days a number of antibiotics
are used to cure a variety of human, animal and plant diseases. Streptomycin,
Erythromycin, Tetracycline etc are some commonly used antibiotics.
Precautions for
taking antibiotics:
Antibiotics should only be taken when advised by a qualified physician.
Moreover it should only be taken when needed otherwise; they became less
effective for future use. Also antibiotics taken unnecessarily may kill the
beneficial bacteria in the body.
Also read
No comments:
Write comments