class 8th computer science chapter 2 solution
Answers
Answer:
Question 1.
Fill in the blanks.
(a) Microorganisms can be seen with the help of a ___
(b) Blue-green algae fix __ directly from the air to enhance the fertility of soil.
(c) Alcohol is produced with the help of ___
(d) Cholera is caused by __
Answer:
(a) microscope
(b) nitrogen
(c) yeast
(d) bacteria
Question 2.
Tick the correct answer.
(a) Yeast is used in the production of
(i) sugar
(ii) alcohol
(iii) hydrochloric acid
(iv) oxygen
Answer:
(ii) alcohol
(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
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 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.
Dead or weakened microbes are used in the preparation of vaccines.
Some bacteria fix atmospheric nitrogen and increase soil fertility.
Algae, yeast, fungi or bacteria may be used as an ingredient or a substitute for protein-rich foods that are suitable for human or animal consumption.
Some microorganisms are taken as probiotics, that are believed to provide health benefits when consumed.
Question 8.
Write a short paragraph on the harms caused by microorganisms.
Answer:
Microorganisms are harmful to us in many ways. For example, microorganisms, called pathogens cause disease in humans, plants and animals. Pathogens or germs enter a healthy body through air, water, contaminated food and infected person by direct or indirect contact or by the carrier. Common ailments like cold, influenza (flu), cough, polio, chicken pox are caused by viruses. Foot and mouth diseases in the cattle are also caused by viruses. Typhoid, tuberculosis (TB) are caused by bacteria. Anthrax a dangerous human and cattle diseases is also caused by bacteria.
Answer: