Science And Technology Solutions Solutions for Class 9 Science Chapter 8 Useful And Harmful Microbes are provided here with simple step-by-step explanations. These solutions for Useful And Harmful Microbes are extremely popular among Class 9 students for Science Useful And Harmful Microbes Solutions come handy for quickly completing your homework and preparing for exams. All questions and answers from the Science And Technology Solutions Book of Class 9 Science Chapter 8 are provided here for you for free. You will also love the ad-free experience on Meritnation’s Science And Technology Solutions Solutions. All Science And Technology Solutions Solutions for class Class 9 Science are prepared by experts and are 100% accurate.

Page No 95:

Question 1:

Complete the statements using the proper option from those given below. Explain the statements.
(mycotoxins, budding, rhizobium)

a. Yeast reproduces asexually by the ............. method.
b. Toxins of fungal origin are called ............. .
c. Leguminous plants can produce more proteins due to ............. .


a. Yeast reproduces asexually by the budding method.
b. Toxins of fungal origin are called mycotoxins.
c. Leguminous plants can produce more proteins due to rhizobium.

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Question 2:

Write the names of microbes found in following food materials.
yoghurt, bread, root nodules of leguminous plants, idli, dosa, spoiled potato curry.


Yoghurt- Lactobacillus
Bread- Saccharomyces
Root nodules of leguminous plants- Rhizobium
Idli- Lactobacillus
Dosa- Lactobacillus
Spoiled potato curry- Clostridium

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Question 3:

Identify the odd word out and say why it is the odd one?

a. Pneumonia, diphtheria, chicken pox, cholera.
b. Lactobacilli, Rhizobia, Yeast, Clostridia.
c. Root rot, Rust (tambera), Rubella, Mozaic.


a. Pneumonia, diphtheria, chicken pox, cholera- Chicken pox is the odd one out because rest of the three diseases are bacterial diseases whereas chicken pox is a viral disease.

b. Lactobacilli, Rhizobia, Yeast, Clostridia- Rhizobia is the odd one out because it is a bacteria which is found in association with plants. All others are bacteria associated with human food products.

c.  Root rot, Rust (tambera), Rubella, Mozaic- Rubella is the odd one out because it is a human disease while rest of the three are plant diseases.

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Question 4:

Give scientific reasons.

a. Foam accumulates on a the surface of ‘dal’ kept for a long time in summer.
b. Why are naphthalene balls kept with clothes to be put away.


a. When dal is soaked in water for a long time in summers, denatured protein are released from dal which mixes with water and form foam. This process occurs quickly in summers because of higher temperatures.

Naphthaline balls sublime slowly. When they are placed in clothes, they sublime without leaving any residue and there role is to ward off any kind of insects which could damage the clothes.

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Question 5:

Write down the modes of infection and the preventive measures against fungal diseases.


Fungal infections are caused by fungi which are found in soil, air, water, as well as on plants, animals, and people. Fungal infections are transmitted to a healthy individual by coming in contact with the spores of the fungi. It may get transmitted by contact with infected soil, water or air. Fungal transmission can also occur from person to person, however the chances of person to person transmission is possible in case of skin infections. Usually fungal infections are not serious, but they can turn out to be serious or even fatal in case of immunocompromised patients for example, people suffering from AIDS.

Measures which can prevent the transmission of fungal diseases are:

  • one should maintain proper hygiene
  • one should avoid sharing of personal products like hair brush
  • avoid direct contact with people who have fungal infection
  • clean or discard the infected objects and garments 
  • wash all bed linen regularly to get rid of any fungal spores
  • one should avoid wearing tight clothes, jeans and shoes
  • keeping areas like feet, groins, underarms and buttocks dry and clean

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Question 6:

Match the pairs.
‘A’ group ‘B’ group

1. Rhizobium a. Food poisoning
2. Clostridium                b. Nitrogen fixation
3. Penicillium                 c. Bakery products
4. Yeast                          d. Production of antibiotics


1. Rhizobium              b. Nitrogen fixation
2. Clostridium a. Food poisoning
3. Penicillium            d. Production of antibiotics
4.  Yeast                     c. Bakery products

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Question 7:

Answer the following questions.

a. Which vaccines are given to infants? Why?
b. How is a vaccine produced?
c. How do antibiotics cure disease?
d. Are the antibiotics given to humans and animals the same? Why?
e. Why is it necessary to safely store the pathogens of a disease against which vaccines are to be produced?


a. There are various kinds of vaccines which are given to infants between 0-12 months. Vaccines are given to young children because their immune systems are not yet fully mature and also because their stomachs produce less acid, making it easier for ingested bacteria and viruses to multiply. These factors make them vulnerable to these serious diseases. Some of the vaccines given to infants are:
Bacille Calmette-Guerin (BCG) vaccination, Hepatitis B, Oral Polio Vaccine (OPV), Rota V etc.

b.  Vaccines are the dead or weakened microorganisms, which help the body fight against diseases. Our body reacts to infection by microorganisms by producing certain substances called antibodies. These antibodies kill the invading microorganisms freeing the body from diseases. So, in order to protect the body from diseases caused by microorganisms, some dead or weakened microbes are introduced into the body, which causes the production of antibodies. These antibodies then remain in the body for a long period of time protecting the body from diseases.

c. Microorganisms have certain biochemical pathways which are needed for their survival; for example, respiration and enzyme synthesis. Antibiotics bind with the precursors needed for these pathways, and block them. In the absence of essential life processes, the microorganisms are killed. For example, penicillin kills a bacterium by blocking the cell wall formation in bacteria. Once the disease causing organism is dead, there is no more spread of the disease and the patient starts recovering.

d. Usually, the diseases which affect animals and humans are different which means their causal organism will also be different. Since, the pathogen of the disease are different, so different antibiotics will be required. However, if the pathogenic organism of a diseases is same for both humans and animals then, antibiotics which are given to humans can be administered to animals as well.

e. Vaccines are dead/weakened microorganisms which provide immunity against diseases by inducing immune response of the body. Since, these microorganisms are dead/weakened, they lose their disease causing abilities and thus pose no harm. However, if these microorganisms are not stored properly and if they are in their infective stage, they can result in widespread of the disease. 

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Question 8:

Answer the following questions in brief.

a. What are ‘broad spectrum antibiotics’?
b. What is fermentation?
c. Define ‘Antibiotic’.


a. Broad spectrum antibiotics are the antibiotics that kill or inhibit a wide range of gram-positive and gram-negative bacteria. Some examples are ofloxacin, vancomycin, chloramphenicol, ampicillin, amoxicillin, etc.

b. The slow decomposition of organic matter into simpler substances in the presence of an enzyme is known as fermentation. The formation of curd from milk is an example of fermentation. The Lactobacilli converts lactose (a type of sugar found in milk) to lactic acid. This reduces the pH and results in separation of milk proteins from the milk an the  yoghurt is formed.

c. An antibiotic is an organic compound produced by a micro-organism that inhibits the growth of or kills other microorganisms.

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