CBSE Guess and Guide for Class 8 NCERT Science
Microorganisms - Friends and Foe
Solutions of CBSE Guess Sample Questions
Short answer type CBSE Guess Questions Answers
Question.1: Where are Microorganisms found?
Answer: Microorganisms are
found everywhere. In air, water and in the bodies of plants and animals. They
can live in all kinds of environment ranging from ice-cold climate to hot
springs and deserts to marshy lands.
Question.2: Which common diseases do viruses cause?
Answer: Viruses cause
diseases like common cold, flue and most of the coughs.
Question.3: Name diseases caused by protozoa?
Answer: Dysentery
and Malaria are caused by protozoa.
Question.4: Name any two algae.
Answer: Chlamydomonas
and Spirogyra.
Question.5: Name any two protozoa.
Answer: Amoeba
and Paramecium.
Question.6: Name any two fungi.
Answer: Rhizopus (bread
mould) and Penicillium.
Question.7: Name unicellular microbes.
Answer: Bacteria, Protozoa
and some Algae.
Question.8: Name multi-cellular microbes.
Answer: Algae and Fungi.
Question.9: Which bacterium is responsible for the curding of
milk?
Answer: Lactobacillus.
Question.10: Which bacterium is used to produce alcohol?
Answer: Yeast.
Question.11: What do you mean by ‘Fermentation’? Who discovered
the process of ‘Fermentation’?
Answer: Conversion of sugar
into alcohol using yeast is called ‘Fermentation’. Louis Pasteur discovered
this process.
Question.12: Which microorganism is not affected by antibiotics?
Answer: Viruses.
Question.13: Name certain diseases which can be prevented by
vaccination?
Answer: Cholera,
tuberculosis, smallpox, hepatitis, polio, etc.
Question.14: Name microorganisms which can fix atmospheric nitrogen.
Answer: Bacteria and Blue
Green Algae.
Question.15: Name one free living bacteria and one blue green
algae who fix nitrogen using oxygen from atmosphere.
Answer: Azotobacter,
Anabaena.
Question.16: What are ‘Pathogens’?
Answer: Disease causing microorganisms
are called ‘Pathogens’.
Question.17: What are communicable diseases?
Answer: Microbial diseases
that can spread from an infected person to a healthy person through air, water,
food or physical contact are called communicable diseases. For example,
cholera, common cold, chicken pox etc.
Question.18: Name an insect which is a common carrier of
microbial diseases.
Answer: House flies.
Question.19: Which microorganism causes diseases like measles,
chicken pox, polio, hepatitis-B, etc?
Answer: Virus.
Question.20: What are preservatives? Name two common
preservatives.
Answer: Chemicals used to
check the growth of microorganisms in food stuffs are called preservatives. Two
common preservatives are salt and edible oil.
CBSE Guess Class
8 Science – CBSE Guide
Microorganisms - Friends and Foe
Long answer type CBSE Guess Questions Answers
Question.1: Write a short note on ‘Nitrogen Fixation’.
Answer: It is a combination
of natural and industrial processes by virtue of which the free atmospheric
nitrogen is converted into nitrogen compounds such as - ammonia, nitrates or
nitrites that is essential for plant growth and is also used in chemical
industries.
Nitrogen
is fixed as nitric oxide by lightening and ultraviolet rays. But more significantly
nitrogen is fixed as ammonia, nitrites and nitrates by soil microorganisms like
- bacterium Rhizobium. Rhizobium lives in the root nodules of leguminous plants
(pulses, peas and beans) with which it has a symbiotic relationship. Due to
nitrogen fixation the fertility of soil is increased.
Question.2: Explain the ‘Nitrogen Cycle’.
Answer:
Nitrogen Cycle
It is a
natural cyclic process in the course of which atmospheric nitrogen enters the
soil and becomes part of living organisms, before returning to the atmosphere.
Nitrogen, an essential part of the amino acids, proteins and nucleic acids is a
basic element of life. Although 78% by volume of the atmosphere is nitrogen
gas, but this gaseous nitrogen must be converted to some usable forms before it
can be consumed by living organisms. This is accomplished through the nitrogen
cycle. Certain bacteria and blue green algae present in the soil fix nitrogen
from atmosphere and convert it into inorganic nitrogen compounds. Such
compounds are directly taken up by plants through their root system. The
nitrogen then passes through the food chain from plants to herbivores to
carnivores. When plants and animals die, bacteria and fungi present in the soil
convert the nitrogenous waste into nitrogenous compounds to be used by plants
again. Certain other bacteria convert some part of these nitrogenous wastes to
free nitrogen through ‘Denitrification’, which goes back into the atmosphere.
As a
result, the percentage of nitrogen in the atmosphere remains more or less
constant.
Question.3: What are the major groups of the microorganisms?
Answer: Major groups of
microorganisms are -
Bacteria: A single-celled, often parasitic microorganism without
distinct nuclei or organized cell structures. Various species are responsible
for decay, fermentation, nitrogen fixation, and many plant and animal diseases.
Fungi: They are long thread-like unicellular as well as
multi-cellular microorganisms.
Algae: Aquatic, photosynthetic microorganisms. In simple terms
they are called sea weeds e.g. Blue Green Algae.
Protozoan: They are unicellular organisms having size ranging from 2 -
200 microns. For example -amoeba, paramecium.
Virus: Viruses are smallest microscopic organisms. They may be rod
- shaped, polygonal, spherical or even cubical. There are four types of viruses
-
1.
Plant viruses
2.
Insect viruses
3.
Bacterial viruses and
4.
Mammalian viruses.
NCERT Solutions for science textbook chapter exercise
Microorganisms:
Friends and Foe - Class 8, Science - NCERT CBSE textbook solutions of chapter
exercise questions [Read]
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