EVENTS
CONVENT HIGH SCHOOL
19/08/2021 CLASS-8 SESSION2021-22(SLOT-1)
SCIENCE
Chapter-2
MICROORGANISMS:FRIEND AND FOE
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Chapter Explanation
(a) Microorganisms can be seen with the help of a microscope
(b) Blue-green algae fix nitrogen directly from the air to enhance
the fertility of soil.
(c) Alcohol is produced with the help of yeast
(d) Cholera is caused by bacteria
Question 2.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
Question 3 Match the organisms in column A with their action in column B.
A B
(i) Bacteria (ii) Fixing
nitrogen
(ii) Rhizobium (iii) Setting of
curd
(iii) Lactobacillus (iv) Baking of bread
(iv) Yeast (v) Causing
malaria
(v) A protozoan (i) Causing
cholera
(vi) A virus (vi) Causing
AIDS
(g) Producing antibodies
Question 4.Can microorganisms be seen with the naked eye? If not, how can
they be seen?
Answer:The microorganisms cannot be seen with our naked eyes because they
are very small in size. Some of these, such as fungus growing on bread, can be
seen with a magnifying glass. Others cannot be seen without the help of a
microscope.
Question 5.What are the major groups of microorganisms?
Answer:Microorganisms are classified on the basis of their size into four
major groups. These groups are:
(a) Bacteria
(b) Fungi
(c) Protozoa
(d) Some algae
Question 6.Name the microorganisms which can fix atmospheric nitrogen in
the soil.
Answer:Rhizobium, Clostridium and Azotobacter.
Question 7.Write 10 lines on the usefulness of microorganisms in our lives.
Answer:Microorganisms are useful to us in many ways. For example,
Bacteria like Lactobacillus convert milk into curd.
Bacteria are also involved in the making of cheese.
Acetobacter aceti is used for producing acetic acid from alcohol.
Yeast is used in the commercial production of alcohol, wine and bakery
products.
Some specific microorganisms are helpful in manufacturing of antibiotics.
Microorganisms act as cleansing agents and decompose the waste products into manure.
Question 8.What are antibiotics? What precautions must be taken while
taking antibiotics?
Answer:Antibiotics are the medicines which kill or stop the growth of the
disease-causing microbes. They are manufactured by growing specific
microorganisms. They are used to cure a variety of diseases.
It is important to take antibiotic only on the advice of a
qualified doctor. One must finish the course prescribed by the doctor to make
the drug more effective. Antibiotics must not be taken unnecessarily because it
may kill beneficial bacteria also. Antibiotics are, however, not effective
against cold and flu as they are caused by viruses.
