Micro-Organisms: Friend and Foe important questions

NCERT Solutions for Class 8th Science Chapter 1 Micro-Organisms: Friend and Foe Questions with answers based on the latest syllabus of CBSE and JKBOSE

Micro-Organisms: Friend and Foe

Exercises

1. Fill in the blanks:

1. (a) Microorganisms can be seen with the help of a microscope.
2. (b) Blue green algae fix nitrogen directly from air to enhance the fertility of soil.
3. (c) Alcohol is produced with the help of yeast.
4. (d) Cholera is caused by bacteria.

2. Tick the correct answer:

(a) Yeast is used in the production of:

Answer: (ii) alcohol

(b) The following is an antibiotic:

Answer: (ii) Streptomycin

(c) Carrier of malaria-causing protozoan is:

Answer: (i) female Anopheles mosquito

(d) The most common carrier of communicable diseases is:

Answer: (ii) housefly

(e) The bread or idli dough rises because of:

Answer: (iii) growth of yeast cells

(f) The process of conversion of sugar into alcohol is called:

Answer: (iii) fermentation

3. Match the organisms in Column I with their action in Column II.

4. Can microorganisms be seen with the naked eye? If not, how can they be seen?

Answer: No, microorganisms cannot be seen with the naked eye. They can be seen with the help of a microscope.

5. What are the major groups of microorganisms?

Answer: The major groups of microorganisms are bacteria, fungi, protozoa, algae, and viruses.

6. Name the microorganisms which can fix atmospheric nitrogen in the soil.

Answer: The microorganisms which can fix atmospheric nitrogen in the soil are Rhizobium, blue-green algae, and some other bacteria.

7. Write 10 lines on the usefulness of microorganisms in our lives.

Answer:

1. Microorganisms play an important role in the nitrogen cycle by fixing nitrogen from the atmosphere.
2. They are used in the production of various dairy products like curd and cheese.
3. Yeasts are used in the baking industry to make bread and cakes rise.
4. Microorganisms are used in the fermentation process to produce alcohol and vinegar.
5. They help in the decomposition of organic matter, thus playing a key role in the recycling of nutrients in the ecosystem.
6. Microorganisms are used in the production of antibiotics like penicillin.
7. They are used in sewage treatment plants to decompose organic waste.
8. Microorganisms help in the digestion process in the gut of animals and humans.
9. They are used in the biotechnology industry for the production of vaccines and other medicines.
10. Microorganisms are employed in genetic engineering to produce genetically modified organisms (GMOs).

8. Write a short paragraph on the harms caused by microorganisms.

Answer: Microorganisms can cause various diseases in humans, animals, and plants. Pathogenic bacteria and viruses are responsible for illnesses such as cholera, tuberculosis, influenza, and AIDS. Fungi can cause infections like athlete’s foot and ringworm. Protozoa can lead to diseases like malaria and amoebiasis. Microorganisms can also spoil food, causing it to decay and produce harmful toxins. Moreover, they can damage crops, leading to significant agricultural losses.

9. What are antibiotics? What precautions must be taken while taking antibiotics?

Answer: Antibiotics are medicines used to kill or stop the growth of bacteria that cause infections. Precautions to be taken while taking antibiotics include completing the full prescribed course, not skipping doses, avoiding self-medication, and not using antibiotics for viral infections. It is also important to follow the doctor’s instructions and not to stop taking the medication even if symptoms improve before the course is complete.

Extended Learning — Activities and Projects Micro-Organisms: Friend and Foe

1. Pull out a gram or bean plant from the field. Observe its roots. You will find round structures called root nodules on the roots. Draw a diagram of the root and show the root nodules.

Answer: This activity involves observing the root nodules of a gram or bean plant, which contain nitrogen-fixing bacteria.

2. Collect the labels from the bottles of jams and jellies. Write down the list of contents printed on the labels.

Answer: This activity involves collecting and analyzing the labels from jams and jellies to understand their contents and preservatives used.

3. Visit a doctor. Find out why antibiotics should not be overused. Prepare a short report.

Answer: This activity encourages students to learn about the dangers of antibiotic overuse, such as antibiotic resistance, and to prepare a report based on their findings.

4. Project: Requirements – 2 test tubes, marker pen, sugar, yeast powder, 2 balloons and lime water.

Steps:

1. Take two test tubes and mark them A and B.
2. Clamp these tubes in a stand and fill them with water leaving some space at the top.
3. Put two spoonfuls of sugar in each of the test tubes.
4. Add a spoonful of yeast in test tube B.
5. Inflate the two balloons incompletely.
6. Tie the balloons on the mouths of each test tube.
7. Keep them in a warm place, away from sunlight.
8. Observe every day for the next 3-4 days.
9. Record observations and think of an explanation.

Further Steps:

1. Take another test tube filled 1/4 with lime water.
2. Remove the balloon from test tube B in such a manner that gas inside the balloon goes into the test tube with lime water.
3. Observe the changes in the lime water.