Microorganisms friend and foe class 8 Solution

Answer the following questions in one sentence

1. What are the major groups of microorganisms?

Microorganisms are divided/classified into four major groups:

1. Bacteria 2. Fungi
3. Algae 3. Protozoa

2. Give the name of any four viral diseases.

Viral diseases are – Polio, Common cold, Hepatitis, Smallpox, Measles etc.

3. Give the name of any four bacterial diseases.

The bacterial disease is as follows –

Cholera, Typhoid, Anthrax, Tuberculosis (TB), Pneumonia etc.

4. Give the name of the disease caused by protozoa.

Malaria & Dysentery are the most common disease caused by protozoans.

5. Give three names of protozoa.

Name of protozoa is Amoeba, Paramecium, and Plasmodium.

6. Give three names of fungi.

Name of Fungi – Bread Mould, Penicillium, Aspergillus, Mushroom.

7. From which is antibiotics production achieved?

Bacteria and fungi are the most common microorganisms from which antibiotic production is achieved.

8. State any four names of antibiotics.

The names of antibiotics are as follows.

Streptomycin. Tetracycline, Erythromycin, Penicillin.

9. How does food poisoning occurs?

Food poisoning occurs due to the consumption of food spoilt by some microorganisms. Microorganisms that grow in our food sometimes produce toxic substances.

10. Give two names of chemical preservatives.

Two chemical methods of food preservation.

  • Preservation by oil and vinegar.
  • Preservation by Sugar.

11. What are called communicable diseases?

A microbial disease that can be spread from an infected person to a healthy person through air, water, food or physical contact is called communicable disease.

6. Define :-

1) Fermentation:-

Anaerobically conversion of sugar into alcohol by yeast is called the Fermentation process.

2) Pasteurisation:-

In pasteurisation, process milk is heated to about 70 0C temperature for 15 to 30 seconds and then suddenly chilled or cooled to 10 0C and then stored.

7. Answer the following questions in short.

1. State the commercial use of microorganisms.

  • Microorganisms are used for the large-scale production of alcohol, wine and vinegar.
  • Yeast microorganism is used for making bread, pastries and cakes in the baking industry.
  • Various dairy products like curd, paneer and cheese are prepared with the help of microorganisms.

2. State the medicinal use of microorganisms.

  • Many microorganisms (Bacteria & Fungi) are used in the production of antibiotics like Penicillin, Streptomycin, Tetracycline and Erythromycin.
  • For the production of vaccines to fight invaders or pathogens.
  • As a food supplement.

3. How is a vaccine helpful to prevent the occurrence of diseases?

  • Vaccines are prepared under the supervision of experts, which fight against invading microorganisms and reduce or completely eliminate the effects of diseases caused by them.
  • The vaccine works in such a way that the human body produces antibodies that fight harmful diseases.

4. State any four usefulness of bacteria.

  • Bacteria are used for the production of vaccines.
  • It is also used to make curd, cheese and paneer.
  • Yeast bacteria are used to make alcohol from sugar.
  • Some bacteria like Rhizobium fix atmospheric nitrogen in the soil and make the soil fertile.

5. State any four uses of Fungi.

  • Used for the preparation of bread and cakes in the bakery industry.
  • Yeast is a unicellular micro-organism used for the production of idli, dosa and fruit juices.
  • They produce antibiotics like penicillin with the help of Penicillium fungus.
  • Fungi are good decomposers that break down complex food into simpler forms.

6. How do pathogens enter our body?

Pathogens are disease-causing microorganisms that enter our bodies through the air we breathe, the water we drink or the food we eat.

7. How is a housefly responsible for the spread of disease?

Whenever flies settle on waste and animal excrement, pathogens stick to their bodies. And when those same flies settle on open food, they transfer the pathogens. Anyone who eats this contaminated food is likely to get sick.

8. How can we control the spread of malaria or dengue?

There are many ways in which a person can avoid these diseases.

  • As we know Mosquitoes breed in water, so water should not be allowed to stagnate here and there.
  • By keeping our surroundings clean and dry, we can prevent mosquitoes from breeding.
  • People should use mosquito nets to avoid mosquito bites.

8. Explain giving scientific reasons.


1) Microorganisms are considered friends and enemies of human beings.

Microorganisms as a friend:-

  • They are useful to make curd from milk, to preparing idli and dosa.
  • Microorganisms decompose plant and vegetable waste to make compost and help clean up the environment.
  • Many microorganisms are used to make medicine. For example – Penicillin

Microorganisms as a foe:-

  • Microorganisms that cause diseases in living beings are known as pathogens. For example- Cholera, Polio, Typhoid etc.
  • Microorganisms spoil the food causing food poisoning.

2) Bacteria are universal.

Microorganisms are everywhere whether it is a hot place or a cold place like-

  • Bacteria are found on the soil and inside the soil which is helpful in fixing nitrogen.
  • These bacteria are also present in such places as – hot springs, marshy lands, snow-covered areas and desert areas.
  • They are also present inside the animal bodies, human bodies including plants.
  • There is no place on the earth where bacteria are absent. So on the basis of these observations, we can say that bacteria are universal.

3.) Water should be boiled and then used during an epidemic.

As we know that in times of epidemic, microorganisms enter the human body through water, food, and air. These microorganisms cause various diseases in the body. Therefore, by boiling water, microorganisms are destroyed, due to which our body remains safe and we are saved from diseases.

4.) Food should always be covered.

Keeping food covered protects your food from harmful bacteria and objects or chemicals entering the food. Therefore covering food can provide the following benefits.

  • Harmful contaminants will not be able to enter the food.
  • Serious consequences like food poisoning can be avoided.
  • House flies that are disease carriers will not be able to spread the pathogen.

9.) Write two points of difference.

Difference between yeast and mould

Yeast Mould
1. Yeast is a unicellular microorganism. 1. Mould is a multi-cellular microorganism.
2. Yeast reproduces asexually2. Mould reproduces both sexually as well as asexually.

Difference between fungus and algae

Fungus Algae
1. Fungus are either parasites or saprophytic. 1. They are autotrophic.
2. There is no chlorophyll or other pigment in their cell. 2. Chlorophyll or other pigments are present in their cells.
3. They are mostly white or black. 3. They are green or of different colours.

Difference between Viruses and Bacteria

Viruses Bacteria
1. Viruses are very small in size and are visible with the help of an electron microscope.1. Bacteria are large in size in comparison to viruses and are visible with a compound microscope.
2. Viruses reproduce only inside the cells of the host organism.2. Bacteria reproduce asexually by binary fission.
3. They don’t have a cellular structure. 3. Bacteria possess a cellular structure.

10.) Classify:

(1) Classify the following microorganisms into bacteria, fungi, algae, and protozoa.

BacteriaLactobacillus, Rhizobium, Pseudomonas
Fungi Penicillium, Yeast, Mucur
AlgaeSpirogyra, Anabaena, Nostoc
ProtozoaAmoeba, Paramecium, Plasmodium

(2) Classify the following diseases as a bacterial disease, viral diseases, protozoan diseases and fungal diseases:

Bacteria DiseaseCholera, Eczema, Typhoid, TB, Pneumonia, Scabies
Viral Disease Polio, Hepatitis, Influenza, Dengue, Chickenpox
Protozoan DiseaseMalaria, Dysentery,
Fungal DiseaseRingworm

11) Match the following properly:

1.) Match the following:

Column AColumn B
1. Protozoand) Causing malaria
2. Rhizobium a) Fixing Nitrogen
3. Lactobacilluse) Setting of curd
4. Yeast c) Baking of bread

2. Match the following:

Column AColumn B
1. Leguminous plant (d) Rhizobium
2. Milk (e) Pasteurisation
3. Preservative(a) Sodium benzoate
4. BCG Vaccine(b) Tuberculosis

12. Answer the following question in detail:

(1) Write 10 lines on the usefulness of microorganisms in our lives.

  • Lactobacillus bacteria are responsible for making curd from milk.
  • Yeast is a unicellular microorganism that is used to convert sugar into alcohol.
  • Yeast is also used to prepare bread, cake, pastries, paneer, cheese etc.
  • Penicillium fungus is used to make penicillin antibiotics.
  • Microorganisms are also responsible for cleaning the environment.
  • Certain microbes are used in sewage treatment.
  • The vaccine is also prepared from microorganisms.
  • Rhizobium bacteria fix atmospheric nitrogen in the soil and increase soil fertility.
  • They are used in the production of wine and vinegar.
  • A fungus known as the mushroom is used as food.

(2) Write a short note: Common methods of food preservation.

There are many ways to preserve food which are given below.

>> Chemical Method:-

Sodium benzoate and sodium metabisulphite are common preservatives. These preservatives are used to check the spoilage of jams and squashes.

>> Preservation by Common Salt:-

Salting is used to preserve amla, raw mangoes, tamarind, meat and fish for ages. Meat and fish are covered with dry salt to check the growth of bacteria.

>> Preservation by Sugar:-

Jams, jellies and squashes are preserved by sugar. Sugar reduces the moisture content which inhibits the growth of microorganisms which spoil food.

>> Preservation by Oil and Vinegar:-

Bacteria cannot survive in environments such as oils and vinegar. Therefore, oil and vinegar are used to prevent the pickle from spoiling.

>> Heat and cold treatment:-

As we know milk is heated and kept in the fridge before it gets spoiled by microorganisms. Similarly, vegetables, fruits, food, meat and fish are also preserved by keeping them in the fridge.

>> Storage and Packing:-

Dry fruits and vegetables are sealed in air-tight packets to prevent the attack of microbes.


(1) To observe microbes in pond water.

Apparatus and Materials:-

Microscope, pond water, Beaker, Glass Slide.


(1) Take some amount of pond water in a beaker.

(2) Spread 1 – 2 drops of water on a glass slide.

(3) Now observe the glass slide under the microscope.


Many microorganisms will be visible on the glass slide.


That means microorganisms are present in pond water.

(2) To observe the growth of yeast in soft dough maida.

Apparatus and Materials:-

A vessel, warm water, yeast powder, 500-gram maida.


>> Take 500-gram maida in a vessel.

>> Then add some sugar and mix with warm/hot water.

>> Now add some amount of yeast powder and knead to make a soft dough.

>> Put that dough for an hour.


The formation of gas bubbles (carbon dioxide) in the dough increases the volume of the dough.


Growth of yeast occurred in the dough of maida.

(3) To observe the fermentation process occurred by yeast in sugar.

Apparatus and Materials:-

Beaker, Sugar, Yeast powder, water.


>> Take a 500 ml beaker and fill it up to 3/4 part with water.

>> Now dissolve 2-3 teaspoons of sugar in it.

>> Add half a spoon of yeast powder to the sugar solution.

>> Keep it covered in a warm place for 4 – 5 hours.

>> Now smell the solution.


The alcoholic smell comes from the sugar solution.


The sugar has been converted into alcohol by yeast.

Finally – Microorganisms Friends and Foe

Basic information related to microorganisms has been shared in this post. If any student has any questions related to this post then you can ask in the comment box.

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