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Tamilnadu Samacheer Kalvi 9th Science Solutions Chapter 22 World of Microbes

Samacheer Kalvi 9th Science World of Microbes Textbook Exercises

I. Choose the correct answer.

World Of Microbes Class 9 Question 1.
Which of the following is transmitted through air?
(a) Tuberculosis
(b) Meningitis
(c) Typhoid
(d) Cholera
(a) Tuberculosis

Chapter 22 World Of Microbes Question 2.
One of the means of indirect transmission of disease is ………………….
(a) sneezing
(b) coughing
(c) vectors
(d) droplet infection
(c) vectors

9th Science World Of Microbes Question 3.
Diptheria affects the ………………………
(a) Lungs
(b) Throat
(c) Blood
(d) Liver
(b) Throat

World Of Microbes Class 9 Pdf Question 4.
The primary organ infected during tuberculosis is …………………..
(a) bone marrow
(b) intestine
(c) spleen
(d) lungs
(d) lungs

Science Solution Class 9 Samacheer Kalvi Question 5.
Microbes that generally enter the body through nose are likely to affect …………………….
(a) gut
(b) lungs
(c) liver
(d) lymph nodes
(b) lungs

9 Samacheer Kalvi Science Question 6.
The organ affected by jaundice is …………………
(a) liver
(b) lungs
(c) kidney
(d) brain
(a) liver

Samacheer Kalvi Guru 9th Science Question 7.
Poliomyelitis virus enters the body through ……………………..
(a) skin
(b) mouth and nose
(c) ears
(d) eye
(b) mouth and nose

II. Fill in the blanks.

  1. ………….. break down organic matter and animal waste into ammonia.
  2. Typhoid fever is caused by ………………
  3. H1N1 virus causes ……………..
  4. ……………… is a vector of viral disease dengue.
  5. ……………. vaccine gives considerable protection against tuberculosis.
  6. Cholera is caused by …………… and malaria is caused by ……………..


  1. Nitrification
  2. Salmonella typhi
  3. Swine Flu
  4. Aedes aegypti mosquito
  5. BCG (Bacillus Calmette Guerin)
  6. Vibrio cholerae, Plasmodium

III. Expand the following

  1. ORS – Oral Rehydration Solution.
  2. HIV – Human Immunodeficiency Virus
  3. DPT – Dipetheria, Pertussis (whooping cough) and Tetanus.
  4. WHO – World Health Organization.
  5. BCG – Bacillus Calmette Guerin

IV. Pick out the odd one.

  1. AIDS, Retrovirus, Lymphocytes, BCG,
  2. Bacterial disease, Rabies, Cholera, Common cold and Influenza


  1. BCG
  2. Rabies

V. State whether True or False. If false write the correct statement.

  1. Rhizobium, associated with root nodules of leguminous plants fixes atmospheric nitrogen – True.
  2. Non- infectious diseases remain confined to the person who develops the disease and do not spread to others – True.
  3. The process of vaccination was developed by Jenner – True.
  4. Hepatitis B is more dangerous than Hepatitis A – True.

VI. Match column A with column B.

Column A Column B
1. Swine flu (a) Human Papilloma virus
2. Genital warts (b) Human Immunodeficiency Virus
3. AIDS (c) Mycobacterium
4. Tuberculosis (d) Influeuza virus HIN 1


  1. (d) Influenza virus H1N1
  2. (a) Human Papillomavirus
  3. (b) Human Immunodeficiency Virus
  4. (c) Mycobacterium

VII. Define the following.

Samacheer Kalvi 9th Science Question 1.
A pathogen is a biological agent that causes disease to its host. e.g. bacteria, virus, etc.

Samacheer Kalvi Guru 9th Question 2.
Bacteriophages are virus that infect bacterial cells, e.g. T4 bacteriophage.

Samacheer Kalvi Class 9 Science Solutions Question 3.
Preparation of antigenic proteins of pathogens (weakened or killed) which on inoculation into a healthy person provides temporary/permanent immunity against a particular disease.

Samacheerkalvi.Guru 9th Science Question 4.
Viral particles which contain only protein. They do not contain nucleic acid.

VIII. Answer the following in brief.

9th Samacheer Kalvi Science Question 1.
Distinguish between Virion and Viroid.

Virion Viroid
Virion is a simple virus particle and can grow and multiply in living cells only Viroid is a free pathogenic RNA of virus.
They are the smallest infecting agents and can live on plants, animals, human beings and bacteria They are found in plant cells and causes diseases only in plants.

9th Science Samacheer Kalvi Question 2.
Name the vector of the malarial parasite. Mention the species of malarial parasite which cause malignant and fatal malaria.
The vector of the malarial parasite is the female Anopheles mosquito. Malaria caused by Plasmodium falciparum is malignant and fatal.

Samacheer Kalvi 9th Standard Science Question 3.
What is triple antigen? Mention the disease which can be prevented by using the antigen.
DPT is called triple antigen vaccine as it is a combined vaccine for protection against Diptheria, Pertusis and Tetanus.

Samacheer Kalvi 9th Science Guide Question 4.
Name the chronic diseases associated with respiratory system.
Chronic diseases associated with respiratory system are; Diptheria, Whooping Cough, Tuberculosis.

Samacheer Kalvi 9th Science Solutions Question 5.
Name the organism causing diarrhoel disease and give one precaution against it.
Cholera (Acute diarrhoeal disease) is caused by Vibrio cholerae through contaminated food, water, oral route and through houseflies. It can be prevented by hygienic sanitary condition, intake of Oral Rehydration Solution (ORS).

Science 9th Samacheer Kalvi Question 6.
Name two common mosquitoes and the diseases they transmit.
Anopheles mosquito and Aedes aegypti mosquito are common mosquitoes that transmit malaria, Chikungunya and Dengue.

IX. Answer in detail.

Science Class 9 Samacheer Kalvi Question 1.
Give an account of classification of bacteria based on the shape.
Bacteria are microscopic, single celled prokaryotic organisms without nucleus and other cell organelles. Although majority of bacterial species exist as single celled forms, some appear to be filaments of loosely joined cells. The size varies from less than 1 to 10 µm in length and 0.2 to 1 µm micrometer in width.
Based on the shapes, bacteria are grouped as:

  1. Spherical shaped bacteria called as cocci (or coccus for a single cell).
  2. Rod-shaped bacteria called as bacilli (or bacillus for a single cell).
  3. Spiral shaped bacteria called as spirilla (or spirillum for single cell)

Samacheer Kalvi.Guru 9th Question 2.
Describe the role of microbes in agriculture and industries.
Microbes play an important role in agriculture as biocontrol agents and biofertilizers. Microbes play a vital role in the cycling of elements like carbon, nitrogen, oxygen, sulphur and phosphorus.

  1. Microbes as biocontrol agents
    Microorganisms used for controlling harmful or pathogenic organisms and pests of plants are called as biocontrol agents (Biopesticides). Bacillus thuringiensis (Bt) is a species of bacteria that produces a protein called as ‘cry’ protein. This protein is toxic to the insect larva and kills them.
  2. Microbes as biofertilizers
    Microorganisms which enrich the soil with nutrients are called as biofertilizers. Bacteria, cyanobacteria and fungi are the main sources of biofertilizers. This is done by microbes either in free living conditions or by having symbiotic relationship with the plants, e.g. Nitrosomonas, Nostoc (free living), symbiotic microbes like Rhizobium, Frankia, mycorrhizae.

Microbes in Industries
Microorganisms play an important role in the production of wide variety of valuable products for the welfare of human beings.

  1. Production of fermented beverages:
    Beverages like wine are produced by fermentation of malted cereals and fruits by Saccharomyces cerevisiae.
  2. Curing of coffee beans, tea leaves and tobacco leaves: Beans of coffee and cocoa, leaves of tea and tobacco are fermented by the bacteria Bacillus megaterium. This gives the special aroma.
  3. Production of curd: Lactobacillus sp. converts milk to curd. .
  4. Production of organic acids, enzymes and vitamins: Oxalic acid, acetic acid and citric acid are produced by fungus Aspergillus niger. Enzymes like lipases, invertase, proteases, and glucose oxidase are derived from microbes. Yeasts are rich source of vitamin-B complex.

Samacheer Kalvi 9th Science Solution Question 3.
Explain the various types of viruses with examples.
Viruses are categorized as:
i. Plant virus: Virus that infect plants, e.g. Tobacco mosaic virus, Cauliflower mosaic virus, Potato virus.
World Of Microbes Class 9 Samacheer Kalvi Science Solutions Chapter 22

ii. Animal virus: Virus that infect animals, e.g. Adenovirus, Retrovirus(HIV), Influenza virus, Poliovirus.
Chapter 22 World Of Microbes Samacheer Kalvi 9th Science Solutions

iii. Bacteriophages: Virus that infect bacterial cells, e.g. T4 bacteriophage.
9th Science World Of Microbes Samacheer Kalvi Chapter 22

Science Samacheer Kalvi 9th Question 4.
Suggest the immunization schedule for a newborn baby till 12 months of age. Why it is necessary to follow the schedule?

Age Vaccine Dosage
New bom BCG 1st dose
15 days Oral Polio 1st dose
6th week DPT and Polio 1st dose
10th week DPT and Polio 1st dose
14th week DPT and Polio 1st dose
9-12 months Measles 1st dose

The immunization schedule must be followed so that the vaccines administered will protect the children in future from infectious and life-threatening diseases.

X. Assertion and Reason.

Mark the correct statement as.
(a) If both A and R are true and R is correct explanation of A.
(b) If both A and R are true but R is not the correct explanation of A.
(c) If A is true but R is false.
(d) If both A and R are false.
Samacheer Kalvi.Guru 9th Science Question 1.
Assertion: Chickenpox is a disease indicated by scars and marks in the body.
Reason: Chickenpox causes rashes on face and further spreads throughout the body.
(a) If both A and R are true and R is a correct explanation of A.

9th Science Solutions Samacheer Kalvi Question 2.
Assertion: Dengue can be treated by intake of antibiotics.
Reason: Antibiotics blocks the multiplication of viruses.
(d) If both A and R are false.

XI. Questions based on thinking skills.

Samacheer Kalvi Science 9th Question 1.
Suggest precautionary measures you can take in your school to reduce the incidence of infectious disease.
Precautionary measures that can be taken are;

  1. The sick student or staff can be asked to stay at home.
  2. Clean and disinfect classroom materials and surfaces.
  3. Adopt healthy practices such as safe handling of food and usage of toilets.
  4. Provide awareness in daily announcements about preventing spread of germs and illnesses.

Question 2.
Tejas suffered from typhoid while, Sachin suffered from tuberculosis. Which disease could have caused more damage and why?
Typhoid is a food and water-borne disease which affects the intestines. There are good drugs available for its treatment. If the patient reports to the doctor on time, it can be treated safely. Typhoid vaccine is also available that can protect against further attacks.

Whereas, Tuberculosis is a very tricky disease. Though it basically infects the lungs, it can spread to other parts of the body such as bones, intestines, etc. Another complication of TB is that, once infected, the Mycobacterium remains dormant in the body even after adequate treatment. Whenever the immunity of the patient goes down, TB can resurface again. Therefore, Tuberculosis causes more damage when compared to Typhoid.


Question 1.
Observe the mosquitoes that are active during the day time. Catch them using an insect net and observe their bodies and legs. What do you observe? Why are cases of Dengue reported in large numbers during the post-monsoon season?
Mosquitoes of Aedes sp. are active during day time. The special features that can be observed in this mosquito is white bands on its legs and a silver-white pattern of scales on its body.

The female mosquitoes lay their eggs above the water line inside containers that hold water. These containers include tires, buckets, birdbaths, water storage jars, and flower pots which are filled with water due to rains. After the mosquitoes lay their eggs, the mosquito larvae hatch which are aquatic and feed on the microorganisms that is found in water necessary for its growth. Hence, Dengue is reported largely during the post-monsoon season.

Question 2.
Recently in 2018, Nipah virus was in the headlines of the daily newspaper. Collect the following information.

  1. What is Nipah virus?
  2. How it gets transmitted?
  3. Mention the preventive measures taken by the government to check the disease.


  1. Nipah virus is a zoonotic virus.
  2. It is transmitted from animals to humans when humans are exposed to secretions from the pigs, or unprotected contact with the tissue of a sick animal.
  3. Nipah virus infection can be prevented by avoiding exposure to sick pigs and bats in endemic areas and not drinking raw date palm sap.
    Routine and thorough cleaning and disinfection of pig farms with appropriate detergents. The infected animals should be slaughtered – with close supervision of burial or incineration of carcasses – may be necessary to reduce the risk of transmission to people.

Samacheer Kalvi 9th Science World of Microbes Additional Questions

I. Choose the correct answer.

Question 1.
…………… can multiply only inside the living cells.
(a) Bacteria
(b) fungi
(c) worm
(d) Virus
(d) Virus

Question 2.
Bacterial cell membranes covered by strong rigid cell wall are made up of ……………….
(a) peptidoglycan
(b) glycogen
(c) polysaccharides
(d) lipopolysaccharides
(a) peptidoglycan

Question 3.
…………….. depend on other organisms or dead organic matter for food.
(a) Parasites
(b) Saprophytes
(c) Heterotrophic bacteria
(d) Symbionts
(c) Heterotrophic bacteria

Question 4.
……………. are the site of protein synthesis
(a) Plasmid
(b) Mitochondria
(c) Cell
(d) Ribosome
(d) Ribosome

Question 5.
Bacteria are ………………… single-celled prokaryotic organisms without a nucleus and other cell organelles.
(a) motile
(b) non-motile
(c) microscopic
(d) anaerobic
(c) microscopic

Question 6.
……………… are either a single or cluster of flagella at both the cell poles.
(a) Lophotrichous
(b) Amphitrichous
(c) Monotrichous
(d) Peritrichous
(b) Amphitrichous

Question 7.
The body of the fungus is called ………………………
(a) thallus
(b) hyphae
(c) mycelium
(d) filament
(a) thallus

Question 8.
…………….. is a complex of several thin filaments called hyphae.
(a) Thallus
(b) Mycelium
(c) Cellulose
(d) Hemicellulose
(b) Mycelium

Question 9.
Typhoid disease is common in children of age group ……………….. years
(a) 2-16
(b) 3-17
(c) 1-15
(d) 4-18
(c) 1-15

Question 10.
Measles is caused by …………………..
(a) Varicella virus
(b) Rhinovirus
(c) Myxovirus parotitis
(d) Rubeola virus
(d) Rubeola virus

II. Fill in the blanks.

  1. ………………. rely on chemical compounds for their energy.
  2. ……………… means proteinaceous infective particle.
  3. ………………. are metabolic products of microorganisms, which in very low concentration are inhibitory or detrimental to other microbes.
  4. Tuberculosis is caused by …………………
  5. ……………….. affects the respiratory tract and causes mild fever, severe cough ending in whoop.
  6. Cholera and typhoid are examples of …………….. disease.


  1. Chemotrophs
  2. Prion
  3. Antibiotics
  4. Mycobacterium tuberculosis
  5. Bordetella pertussis
  6. waterborne

III. Expand the following

  1. AIDS – Acquired Immuno Deficiency Syndrome
  2. TT – Tetanus Toxoid.
  3. DT – Diphtheria and Tetanus

IV. State whether true or false

  1. Microorganisms that are killed by heat or chemicals are live vaccines – False
    Correct Statement: Microorganisms that are killed by heat or chemicals are killed vaccines.
  2. DT is a dual or combined antigen – True
  3. Poliovirus is also called enterovirus – True
  4. Malaria is caused by bacteria – False
    Correct Statement: Malaria is vector-borne disease caused by Plasmodium sp. a protozoan.
  5. Dengue is also known as break-bone fever – True

V. Match column A with column B.

Question 1.

S.No. Column A Column C
1. Genital Herpes a. Neisseria gonorrhoea
2. Gonorrhoea b Treponema pallidum
3. Syphilis c Plasmodium sp.
4 Malaria d Herpes Simplex Virus


S.No. Column A Column C
1. Genital Herpes a. Herpes Simplex Virus
2. Gonorrhoea b Neisseria gonorrhoea
3. Syphilis c Treponema pallidum
4 Malaria d Plasmodium sp.

VI. Analyze the table and select the option given below that correctly fills the blank

Disease Causative organism Symptoms
Swine flu Fever, cough, headache
Filaria Nematode
Chikungunya RNA virus
Cholera vomiting, nausea, and dehydration

(Joint pain, body rashes, headache, Vibrio cholerae, Fever, Inilueuza virus H1N1)

Disease Causative organism Symptoms
Swine flu Influenza virus H1N1 Fever, cough, headache
Filaria Nematode Fever
Chikungunya RNA virus Joint pain, body rashes, headache
Cholera Vibrio cholerae vomiting, nausea and dehydration

VII. Define the following.

Question 1.
Pathogens of certain diseases reach the human body through intermediate agents which act as carrier or vector, (eg) Housefly, Mosquito.

Question 2.
Infective stage of Plasmodium (Malarial parasite) which infect man and transmitted from salivary gland of mosquito.

Question 3.
Peptidoglycan is a combination of sugars and amino acids that forms the cell wall of most bacteria.

VIII. Answer in brief.

Question 1.
Write a short note on Fungi.
Fungi are larger than bacteria. They lack chlorophyll, hence depend on living or dead host for their nutritional needs. They are spherical in shape.

Question 2.
What is Creutzfeldt-Jakob disease?
Creutzfeldt-Jakob disease is a neurodegenerative disease. As a result of this disease cerebral cortex is affected and it is characterised by progressive dementia, memory loss, behavioral changes, poor coordination and visual disturbances.

Question 3.
What are the disease categories based on microbes?
Microbial Disease can be categorized based on:

  1. The extent of occurrence (endemic, epidemic, pandemic or sporadic).
  2. Whether infectious or non-infectious.
  3. Types of pathogen – whether caused by bacterial, viral, fungal or protozoan infections.
  4. Transmitting agent – whether airborne, waterborne or vector-borne.

Question 4.
Define the incubation period.
The interval between infection and the first appearance of a disease is called incubation period. It may vary from few hours to several days.

Question 5.
What is Diptheria?
Diptheria is caused by Corynebacterium diphtheriae. It generally affects the upper respiratory tract (nose and throat) and causes fever, sore throat and choking of air passage.

Question 6.
Write about Dengue.
Dengue is known as break-bone fever. The name break bone fever was given because of the contortions caused due to the intense joint and muscle pain. Dengue haemorrhagic fever is a more severe form and can be life threatening or fatal.

Question 7.
What is immunization?
Immunization is a process of developing resistance to infections by the administration of antigens or antibodies. It is an effective way of controlling the spread of infection by strengthening the host defenses.

IX. Answer in detail.

Question 1.
Explain vector borne diseases.
Vector is an agent that acts as an intermediate carrier of the pathogen. Many insects and animals acts as vectors. Diseases transmitted by vectors are called vector borne diseases. These vectors can transfer infecting agents from an infected person to another healthy person. Some of the insect vector borne diseases are Malaria, Filaria, Chikungunya, Dengue, and the diseases which are transmitted through animals are Bird flu and Swine flu.

  • Malaria continues to be one of the major health problems of developing countries. Malaria is caused by protozoan parasite Plasmodium. Four different species of Plasmodium namely, P. vivax, P. malariae, P. falciparum and P. ovale cause malaria. Malaria caused by Plasmodium falciparum is malignant and fatal.
  • Chikungunya, which is caused by single stranded RNA vims, is transmitted in humans by the bite of infected Aedes aegypti mosquito during the day time. It causes severe and persistent joint pain, body rashes, headache and fever. Joint pains can last for a very long time.
  • Dengue is known as break bone fever. The name break bone fever was given because of the contortions caused due to the intense joint and muscle pain. It is transmitted by Aedes aegypti mosquito that has previously bitten an infected person.

Question 2.
Write in detail about the diseases transmitted by animals.
Diseases Transmitted by Animals:
Swine Flu is so termed because the virus that first caused the disease had originated from pigs. People with weak immune system are at high risk of contracting swine flu. It is an acute respiratory virus which is contagious and spreads through air. Swine flu is caused by virus that affects pigs and has started infecting humans as well. Influeuza virus FI1N1 has been identified as the cause of this disease.

Avian influenza is a contagious bird disease caused by a number of viruses. Birds that can carry and spread an avian influenza virus include poultry (like chickens, turkeys or ducks), wild birds and even pet birds.

Question 3.
Explain about the waterborne diseases.
Microbes present in the contaminated water cause various infectious diseases. Some of the water borne diseases are cholera, typhoid, infectious hepatitis, poliomyelitis, diarrhoea, etc.

  • Cholera is an epidemic disease and in the earlier days many people died due to this. It is caused by Vibrio cholerae mostly due to contaminated food and water. Acute diarrhoea with watery stool, vomiting, nausea and dehydration are the symptoms of this disease.
  • Typhoid is common in children of age group 1-15 years. Nearly 2.5 million people suffer from typhoid disease every year. This is caused by the bacteria Salmonella typhi. Food and water contaminated by the faeces of infected person causes this disease. Infected persons show symptoms of fever, weakness and vomiting.
  • Poliomyelitis is caused by polio virus and spreads from person to person. This virus gets into the blood and enters into the brain or spinal cord and affects the central nervous system. Muscles get paralysed and result in difficulty in walking.
  • Hepatitis A or Infectious Hepatitis is caused by Hepatitis A virus (HAV). It is transmitted through contaminated water and food and through oral route. It causes inflammation of liver resulting in jaundice (Yellow fever).
  • Acute diarrhea is commonly caused by infection of intestine. It is caused by Rotavirus and results in sudden onset of frequent stools, three or more in a day. It is transmitted through contaminated water and food. Increased fluidity and the volume of bowel movements result in excessive loss of fluid and electrolytes from the intestine.

Question 4.
Write short notes on antibiotics and vaccines.
Antibiotics are metabolic products of microorganisms, which in very low concentration are inhibitory or detrimental to other microbes. In 1929, Alexander Fleming produced the first antibiotic pencillin. In human beings antibiotics are used to control infectious diseases like cholera, diptheria, pneumonia, typhoid, etc.

Class of Microorganisms Type of Microorganism Antibiotic produced
Streptomyces griseus Streptomycin
Bacteria Streptomyces erythreus Erythromycin
Bacillus subtilis Bacitracin
Fungi Penicillium notatum Penicillin
Cephalosporium acremonium Cephalosporin

Vaccines are prepared by killing or making the microbes inactive (attenuated). These inactive microbes are unable to cause the disease, but stimulate the body to produce antibodies against the antigen in the microbes.

Type of Vaccine Name of the vaccine Disease
Live attenuated MMR Measles, Mumps and Rubella
BCG (Bacillus Calmette Guerin) Tuberculosis
Inactivated (Killed antigen) Inactivated polio virus (IPV) Polio
Subunit vaccines (Purified antigens) Hepatitis B vaccine Hepatitis B

(Inactivated antigen)

Tetanus toxoid (TT) Tetanus
Ditpheria toxoid Diptheria