Important Questions for Chapter-2 Microorganisms: Friend and Foe

Important questions for CBSE Class 8 Science Chapter -2 Microorganisms: Friend and Foe

This page is prepared by the HT experts and consists of all the important questions chapter-wise; you can find important questions for CBSE class 8 science Chapter -2 Microorganisms: Friend and Foe. Chapter -2 Microorganisms: Friend and Foe required a good understanding of the theory so before solving the given questions read the theory given in the NCERT textbook for Chapter -2 Microorganisms: Friend and Foe. Check out the list of chapter-wise Important questions for class 8 science prepared by experts do follow NCERT Solutions for class 8. 

Important Questions for Class 8 Science consists of Subjective Questions of the following Types 

Section-1 It consists of the Most Important Questions from Chapter -2 Microorganisms: Friend and Foe having 5 Marks with solutions

Section-2. It consists of the Most Important Questions from Chapter -2 Microorganisms: Friend and Foe having 3 Marks with solutions

Section-3. It consists of the Most Important Questions from Chapter -2 Microorganisms: Friend and Foe having 2 & 1 Marks with solutions

Q1.What do you understand by microorganisms?

Ans. Microorganisms are living organisms which can not be seen with our unaided eyes. 

They have a high degree of adaptability and can survive in all kinds of environments, like hot springs, ice-cold water, saline water, desert soil or even in marshy land. They are present even in the human body, in dead organisms, and as parasites. Their body is generally covered by a hard outer coating called the cyst.

Q2. Describe the useful and harmful effects of microorganisms.

Useful effects:

1. They help in the formation of curd, and cheese. 

2.  Convert the fruit juices into vinegar and wine.

3. Decompose the complex organic material into simple inorganic molecules.

4. Help in tanning the leather.

5. Some help in fixing atmospheric nitrogen.

6. Some of them present in the intestine help in the process of digestion.

Harmful effects:

1. They cause a large variety of diseases in plants, animals and human beings.

2. They spoil food items as well as clothes, leather etc. 

Q3. How can you culture the microorganisms? Describe the process in brief.

Ans. To culture the microorganisms the medium should be suitable for their growth. 

It should have the proper amount of acidity, alkalinity, oxygen and temperature.

Potato dextrose agar (PDA) medium can be prepared in the classroom/laboratory.

Take 200 g of healthy potato tubers and wash them properly.

Cut them into pieces and boil them in water till they become soft. Crush and cool it. Add 500ml. distilled water and 20g. glucose. 20 g. plain agar boiled in 500 ml. water is added to the above mixture. Store the mixture obtained, in suitable containers. Now the mixture is ready for use. Another commonly used culture medium is yeast extract prepared from yeast and carbohydrates.

Q4. List out any two important landmarks in the study of micro-organisms.

Ans. i) Robert Hooke observed bacteria with a simple microscope.

      ii) Louis Pasteur observed that microbes arise from the preexisting ones.

Q5. State any one useful effect of microorganisms in our life. 

Ans. Many bacteria found in the human intestine help in the process of digestion.

Q6. Name three habitats of microorganisms. 

Ans. Soil, water and animal body.

Q7. Describe the various types of bacteria with examples. 

Ans. Based on the shapes, the bacteria can be divided into three categories:

Bacillus or rod-shaped: e.g. Lactobacillus. Bacillus and Pseudomonas.

Coccus or round shaped: eg. Streptococcus, Sarcina and micrococcus.

Spirillum or spiral rod: eg.Vibrio, Treponema and Campylobacter.

Q 8. State some beneficial effects of bacteria.

Ans. Some beneficial effects of bacteria:

They help in the formation of curd, and cheese. Convert the fruit juices into vinegar and wines. Decompose the complex organic material into simple inorganic molecules. Help in the tanning of the leather. Some help in fixing atmospheric nitrogen.

Q9. Describe the role of blue-green algae.

Ans. They make nitrogen available to the soil.

They increase the humus content of the soil.

Improve the water-holding capacity of the soil.

Support crop growth.

Q10.Mention two important uses of fungi.

Ans.  Fungi help in the process of fermentation.

         Helps in the decomposition of dead organic matter.

Q 11. N ame any two food items that are prepared using yeast. 

Ans. Bread and dosa. 

Q12.Name any two diseases caused by mycoplasma. (2 marks)

Ans. i) Pleuropneumonia in domestic animals.

        ii)Witch’s broom in plants.

Q 13. “Viruses are living or non-living.” Comment with reasons. (2 marks)

Ans. Viruses are considered the connecting link between living and nonliving. The reasons for being nonliving are: they neither grow nor reproduce once outside the host.

They can be considered living as they multiply very fast and grow when entered the host.

Q14. What is the basis of the classification of viruses? (3 marks)

Ans. Viruses are mostly classified based on the host they inhabit, the disease produced or the symptoms of the disease. e.g.TMV –Tobacco Mosaic Virus got its name from the host tobacco and the mosaic-like patches produced as symptoms. Viruses attacking bacteria are called Bacteriophages. Phage means eater.

Q15. Name any five protozoans known to you. (2 marks)

Ans. Amoeba, Paramecium, Euglena, Plasmodium and Entamoeba.

Q 16. Describe how microorganisms help in sewage treatment. 

Ans.  In sewage treatment aerobic bacteria like Bacillus, Pseudomonas and Proteus are used for the purpose. Oxygen is pumped where the bacteria are present in the sewer tanks.

In a few hours, the bacteria bring about rapid decomposition of sewage.

Undigested sewer is then transferred to an anaerobic digestion tank where in final digestion methane gas is produced. This gas is biogas used as fuel.

The sludge left is rich in nitrogen and is used as manure after drying.

Q18. Describe the mode of nutrition in bacteria. (3 marks)

Ans. Mode of nutrition:

   i) Autotrophs-they synthesize their food.

   ii) Heterotrophs-take the readymade food synthesized by others.

Autotrophs are further of two types; a) phototrophs use the energy of the sun b) chemotrophs use the energy of inorganic compounds. Heterotrophs bacteria may be either saprophytic or parasitic.

Q19. Describe the mode of reproduction in bacteria. (3 marks)

Ans. Reproduction in bacteria: the rate of multiplication of bacteria under favourable

       conditions of temperature, nutrition, moisture, and pH. The common methods

       are:

       i) Cell division

       ii) Binary fission

       iii) Endospore formation in unfavourable conditions.

       iv) by sexual means also.

Q21.Explain how blue-green algae help in increasing the fertility of the soil.  (2 marks)

Ans. The blue-green algae help in increasing the fertility of the soil by fixing the atmospheric nitrogen into usable for mmmm.

Q 23.  Describe the main characteristics of the viruses in brief. (3 marks)

Ans. 

They are the smallest living beings.

They lack cellular structure.

They can be crystallized and can be stored for a long time.

They are nonliving outside the host and living once inside the host.

Q24.List out the main differences between, bacteria, mycoplasma and viruses.  

Ans. Bacteria have the primitive type of cell division, do not have membrane-bound organelles, not have have have organized nuclei but have a rigid cell wall.

Mycoplasma is nonmotile, and and and lacks a celwallsll aisisry small and spherical.

Viruses lack cellular structure they lie at the borderline betweentweentween living and nonliving.

Q25. How do algae take food? (1 mark)

Ans. They prepare their foodthroughroughroughroughy the process of photosynthesis.

Q26.Can we find a place without microbes in nature? (1 mark)

Ans.No, we can not find any place on the earth without microbes.

Q27. Which microorganism is used in the production of alcohol? (1 mark)

Ans.Yeast.

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