NCERT Solutions for Class 8 Science Chapter 2 Exercise
Chapter 2 – Microorganisms: Friend and Foe
These are the NCERT Solutions for Class 8 Science. They cover textbook questions extra questions, example problems, worksheets multiple-choice questions, and short answer questions. Answering these questions helps you organize your notes better and gain a complete grasp of the subject.
Questions:
1) Fill in the blanks:
(a) Microorganisms can be seen with the help of a ____________.
(b) Blue-green algae fix __________ directly from the air and enhance the fertility of the soil.
(c) Alcohol is produced with the help of __________.
(d) Cholera is caused by __________.
Solutions:
a) Microscope
b) Nitrogen
c) Yeast
d) Bacteria (Vibrio cholera)
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) The carrier of a 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 converting sugar into alcohol is called
(i) nitrogen fixation; (ii) moulding; (iii) fermentation; (iv) infection
Solutions:
a) (ii) alcohol
b) (ii) Streptomycin
c) (i) female Anopheles mosquito
d) (ii) housefly
e) (iii) growth of yeast cells
f) (iii) fermentation
3) Match the organisms in Column A with their actions in Column B.
A
B
Bacteria
Fixing Nitrogen
Rhizobium
Fixing of curd
Lactobacillus
Baking of bread
Yeast
Causing Malaria
Protozoa
Causing Cholera
A Virus
Causing AIDS
Producing Antibodies
Solutions:
A
B
Bacteria
Causing Cholera
Rhizobium
Fixing Nitrogen
Lactobacillus
Setting of Curd
Yeast
Baking of Bread
Protozoa
Causing Malaria
A Virus
Causing AIDS
Producing Antibodies
4) Can microorganisms be seen with the naked eye? If not, how can they be seen?
Solution:
Microorganisms are tiny, so they can’t be seen with the naked eye. Some fungus growth on bread can be seen with a magnifying glass. A powerful microscope is used to see the microorganisms clearly.
5) What are the major groups of microorganisms?
Solution:
The major groups of microorganisms include:
Bacteria
Virus
Fungi
Algae
Protozoa
6) Name the microorganisms that can fix atmospheric nitrogen in the soil.
Solution:
Rhizobium
7) Write 10 lines on the usefulness of microorganisms in our lives.
Solution:
Some of the usefulness of microorganisms in our lives is mentioned below.
Lactobacillus-type bacteria use milk to make curd.
Cheese is also made with the help of bacteria.
The bacteria Acetobacter aceti produces acetic acid from alcohol.
Commercial manufacturing of wine, beer, and baked goods all employs yeast.
Bacteria and yeast are used for the fermentation of rice idlis and dosa batter.
Certain bacteria are useful in the production of antibiotics.
Microorganisms break down waste materials into manure and serve as cleaning agents.
Vaccines are made with either dead or weakened microorganisms.
Certain microorganisms improve soil fertility by removing nitrogen from the atmosphere.
Algae, yeast, fungi, or bacteria can be utilized as components to make foods high in protein suitable for human or animal consumption.
8) Write a short paragraph on the harmful effects of microorganisms.
Solution:
Microorganisms can harm us in some ways. For instance, pathogens are microbes that cause human, plant, and animal diseases. Viruses are the source of many common illnesses, such as chicken pox, polio, cough, and influenza. Bacteria cause tuberculosis, typhoid, and the deadly animal and human disease anthrax. Protozoa produce diseases, including malaria and dysentery. Furthermore, food deterioration and food poisoning are caused by microorganisms.
9)What are antibiotics? What precautions must be taken while taking antibiotics?
Solution:
Antibiotics are drugs used to treat a disease by eradicating or preventing the growth of microorganisms that cause the illness. Only a licensed medical professional should prescribe antibiotics. One must also finish the course as prescribed by the doctor.
