NCERT Guide - Class 8, CBSE Science, Microorganisms Friends and Foe - Answers for CBSE Guess Questions


CBSE Guess and Guide for Class 8 NCERT Science

Microorganisms - Friends and Foe

Solutions of CBSE Guess Sample Questions

  Short answer type CBSE Guess Questions Answers
Question.1: Where are Microorganisms found?
Answer: Microorganisms are found everywhere. In air, water and in the bodies of plants and animals. They can live in all kinds of environment ranging from ice-cold climate to hot springs and deserts to marshy lands.
Question.2: Which common diseases do viruses cause?
Answer: Viruses cause diseases like common cold, flue and most of the coughs.
Question.3: Name diseases caused by protozoa?
Answer: Dysentery and Malaria are caused by protozoa.
Question.4: Name any two algae.
Answer: Chlamydomonas and Spirogyra.
Question.5: Name any two protozoa.
Answer: Amoeba and Paramecium.
Question.6: Name any two fungi.
Answer: Rhizopus (bread mould) and Penicillium. 
Question.7: Name unicellular microbes.
Answer: Bacteria, Protozoa and some Algae.
Question.8: Name multi-cellular microbes.
Answer: Algae and Fungi.
Question.9: Which bacterium is responsible for the curding of milk?
Answer: Lactobacillus.
Question.10: Which bacterium is used to produce alcohol?
Answer: Yeast.
Question.11: What do you mean by ‘Fermentation’? Who discovered the process of ‘Fermentation’?
Answer: Conversion of sugar into alcohol using yeast is called ‘Fermentation’. Louis Pasteur discovered this process.
Question.12: Which microorganism is not affected by antibiotics?
Answer: Viruses.
Question.13: Name certain diseases which can be prevented by vaccination?
Answer: Cholera, tuberculosis, smallpox, hepatitis, polio, etc.
Question.14: Name microorganisms which can fix atmospheric nitrogen.
Answer: Bacteria and Blue Green Algae.
Question.15: Name one free living bacteria and one blue green algae who fix nitrogen using oxygen from atmosphere.
Answer: Azotobacter, Anabaena.
Question.16: What are ‘Pathogens’?
Answer: Disease causing microorganisms are called ‘Pathogens’.
Question.17: What are communicable diseases?
Answer: Microbial diseases that can spread from an infected person to a healthy person through air, water, food or physical contact are called communicable diseases. For example, cholera, common cold, chicken pox etc.
Question.18: Name an insect which is a common carrier of microbial diseases.
Answer: House flies.
Question.19: Which microorganism causes diseases like measles, chicken pox, polio, hepatitis-B, etc?
Answer: Virus.
Question.20: What are preservatives? Name two common preservatives.
Answer: Chemicals used to check the growth of microorganisms in food stuffs are called preservatives. Two common preservatives are salt and edible oil.
  CBSE Guess Class 8 Science – CBSE Guide
Microorganisms - Friends and Foe
Long answer type CBSE Guess Questions Answers
Question.1: Write a short note on ‘Nitrogen Fixation’.
Answer: It is a combination of natural and industrial processes by virtue of which the free atmospheric nitrogen is converted into nitrogen compounds such as - ammonia, nitrates or nitrites that is essential for plant growth and is also used in chemical industries.
Nitrogen is fixed as nitric oxide by lightening and ultraviolet rays. But more significantly nitrogen is fixed as ammonia, nitrites and nitrates by soil microorganisms like - bacterium Rhizobium. Rhizobium lives in the root nodules of leguminous plants (pulses, peas and beans) with which it has a symbiotic relationship. Due to nitrogen fixation the fertility of soil is increased. 
Question.2: Explain the ‘Nitrogen Cycle’.
Nitrogen Cycle
It is a natural cyclic process in the course of which atmospheric nitrogen enters the soil and becomes part of living organisms, before returning to the atmosphere. Nitrogen, an essential part of the amino acids, proteins and nucleic acids is a basic element of life. Although 78% by volume of the atmosphere is nitrogen gas, but this gaseous nitrogen must be converted to some usable forms before it can be consumed by living organisms. This is accomplished through the nitrogen cycle. Certain bacteria and blue green algae present in the soil fix nitrogen from atmosphere and convert it into inorganic nitrogen compounds. Such compounds are directly taken up by plants through their root system. The nitrogen then passes through the food chain from plants to herbivores to carnivores. When plants and animals die, bacteria and fungi present in the soil convert the nitrogenous waste into nitrogenous compounds to be used by plants again. Certain other bacteria convert some part of these nitrogenous wastes to free nitrogen through ‘Denitrification’, which goes back into the atmosphere.
As a result, the percentage of nitrogen in the atmosphere remains more or less constant.
Question.3: What are the major groups of the microorganisms?
Answer: Major groups of microorganisms are - 
Bacteria: A single-celled, often parasitic microorganism without distinct nuclei or organized cell structures. Various species are responsible for decay, fermentation, nitrogen fixation, and many plant and animal diseases.
Fungi: They are long thread-like unicellular as well as multi-cellular microorganisms.
Algae: Aquatic, photosynthetic microorganisms. In simple terms they are called sea weeds e.g. Blue Green Algae.
Protozoan: They are unicellular organisms having size ranging from 2 - 200 microns. For example -amoeba, paramecium.
Virus: Viruses are smallest microscopic organisms. They may be rod - shaped, polygonal, spherical or even cubical. There are four types of viruses -
1.      Plant viruses
2.      Insect viruses
3.      Bacterial viruses and
4.     Mammalian viruses.

NCERT Solutions for science textbook chapter exercise

Microorganisms: Friends and Foe - Class 8, Science - NCERT CBSE textbook solutions of chapter exercise questions [Read]

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