Microorganisms: Friend and Foe

Earth is the only planet known to have life on it. We have organisms all around us going through a number of cycles to be a part of the living world. What demarcates a living being from a non-living being is the life processes that a living organism must go through to ensure its survival on the planet. Let us read more about Microorganism Friend and Foe Class 8. 

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What are Microorganisms?

Microorganisms are living organisms that are very minute to be seen by the naked eye and can be classified into four major groups namely bacteria, fungi, protozoa and some algae. Bacteria are unicellular, while some have well developed, multicellular body like moulds and can survive under different types of climatic environment, ranging from ice cold climate to hot summers and deserts to marshy, muddy lands. Often they are found living inside the bodies of animals including humans, air, water, soil, food and other things.

Download the Entire Microorganisms- Friends and Foe Chapter on NCERT

Classification of Microorganisms

Microorganisms can be classified into various sub groups on the basis of their size and cellularity. In this section we shall discuss each of the sub group:

Virus: Viruses have a unique character as they can be crystallized and stored like some non-living things, such as common salt and sugar and on the other hand they can also multiply like living organisms when they are within a living body.

Bacteria: Bacteria are single celled microorganisms, that come under the plant kingdom because they have rigid definite cell wall like plant cells. 

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Fungi: Also known as non-green plants, they cannot synthesize their own food and have to be dependent on others for their food. Most fungi take their food from dead organic matter. Some live on other organisms as parasites.

Algae: Algae are green substances floating on the surface of stagnant water and tend to grow on wet surfaces. One remarkable feature is that they are capable of synthesizing their own food. 

Protozoa: Unicellular animals, some are free-living, others are parasites. Several parasitic protozoans can cause diseases in human beings, domestic animals and plants. For example, Plasmodium, a protozoan, causes malaria.

Characterstics of Microorganisms

• Commercially used for the large scale production of alcohol, wine and acetic acid (vinegar), microorganisms can be harmful too. 
• Some of the microorganisms known as pathogens can cause diseases in humans, plants as well as in animals. 
•  Some microorganisms are capable of spoiling leather, food and clothing.

Microbial Diseases

Like we discussed microorganisms can be harmful too. Microorganisms are known for cousin severe diseases in humans, some of which we have listed below:

• Viruses: Common Ailments: Cold, Cough, and Influenza (or Flu) and Serious Diseases: Polio, Chicken Pox, Measles etc
• Bacteria: Tuberculosis and Typhoid
• Protozoa: Dysentery and Malaria

ALso Read:NCERT Class 8 SST Syllabus

What is Food Poisoning?

Food poisoning is a result of consumption of food spoiled by some microorganisms that produce substances that are toxic in nature and make the food poisonous and can cause serious illness to living organisms.

Food Preservation– Microorganisms may grow on our food and spoil it. Spoiled food emits bad smell,bad taste and changes colour.

Also Read: NCERT Class 8 Maths Syllabus

What is Antibody?

Next In the chapter Microorganisms- Friend and Foe, when disease causing microbes enter our body, our internal defensive mechanisms produce antibodies to fight disease causing microbes.

When a disease-carrying microbe enters our healthy body, antibodies are produced by the body, to kill the microbes. The antibodies then remain in the body for a long time to  protect us from the disease causing microbes. The substance which is injected into the body to trigger the body to initiate this entire process is called a vaccine.

• Pasteurization- This process was discovered by Louis Pasteur in which milk is heated to 70 degree Celsius for about 15 to 30 seconds and then chilled and stored. 
• Nitrogen Cycle- 
  • Some bacteria and blue-green algae present in the soil fix nitrogen from the atmosphere and convert it into compounds of nitrogen. 
  • Once nitrogen is converted into these usable compounds, it can be utilised by plants from the soil through their root system.
  • When plants and animals die, bacteria and fungi present in the soil convert the nitrogenous wastes into nitrogenous compounds to be used by plants again. 
  • Thus due to this Nitrogen Cycle, the percentage of nitrogen in the atmosphere remains more or less constant.

Also Read: List of NCERT Books Class 8

NCERT Solutions for Microorganisms- Friend and Foe 

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 A with their action in column B.

Answer : (i) (e) ; (ii) (a) ; (iii) (b) ; (iv) (c)  ; (v) (d) ; (vi) (f)

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

Answer : Although microorganisms cannot be seen by our naked eyes because of the extremely minute size, some of these, such as fungus growing on bread, can be seen with a magnifying glass

5. What are the major groups of microorganisms?

Answer: Microorganisms are classified on the basis of their size into four major groups. These groups are:a) Bacteria b) Fungi c) Protozoa and d) algae

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

Answer: Rhizobium, Clostridium and Azotobacter.

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

Answer: Microorganisms are useful to us in many ways. 

• Bacteria like Lactobacillus convert milk into curd.
• Bacteria used to make cheese.
• Acetobacter aceti is used for producing acetic acid from alcohol.
• Yeast is used in the commercial production of alcohol, wine and bakery products.
• Some specific microorganisms are helpful in manufacturing of antibiotics.
• Microorganisms act as cleansing agents and decompose the waste products into manure.
• Dead or weakened microbes are used in the preparation of vaccines.
• Some bacteria fix atmospheric nitrogen and increase soil fertility.
• Algae, yeast, fungi or bacteria may be used as an ingredient or a substitute for protein-rich foods that are suitable for human or animal consumption.
• Some microorganisms provide health benefits when consumed as probiotics.

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

Answer: Commercially used for the large scale production of alcohol, wine and acetic acid (vinegar), microorganisms can be harmful too. Some of the microorganisms known as pathogens can cause diseases in humans, plants as well as in animals. Some microorganisms are capable of spoiling leather, food and clothing.

• Microbial Diseases: Viruses: Common Ailments: Cold, Cough, and Influenza (or Flu) and Serious Diseases: Polio, Chicken Pox, Measles etc
• Bacteria: Tuberculosis and Typhoid
• Protozoa: Dysentery and Malaria

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

Answer: Antibiotics are the medicines that are consumed to stop the growth of disease-causing microbes. They are used to cure a variety of diseases.
Antibiotics must be consumed only on the advice of a qualified doctor. One must finish the course prescribed by the doctor to make the drug more effective. Antibiotics must not be taken unnecessarily because it may kill beneficial bacteria also. 

This was all about the various microorganisms friends and foe class 8. For more such informative content , stay connected to Leverage Edu!