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Chapter 9a

Economic Importance of Bacteria

Class 9 - Concise Biology Selina

Progress Check 1

Question 1

Name the four common shapes of bacteria.


  1. Cocci (spherical bacteria)
  2. Bacilli (rod-shaped bacteria)
  3. Spirilla (twisted or spiral bacteria)
  4. Vibrio (comma-shaped)

Question 2

Give the technical terms for the following patterns of occurrence of bacteria

  1. In pairs ...............
  2. In long chains ...............
  3. In clusters ...............


  1. Diplococci
  2. Streptococci
  3. Staphylococci

Question 3

List the kinds of nutrition in bacteria.


Bacteria mostly shows saprotrophic and parasitic nutrition.

Question 4

What is the common method of reproduction in bacteria?


The common method of reproduction in bacteria is fission or cell division.

Question 5

Why do bacteria produce spores ?


Bacteria produce spores to overcome unfavourable conditions.

Multiple Choice Type

Question 1

Bacteria are no more classified as plants primarily because:

  1. These are unicellular and prokaryotic
  2. These are motile
  3. Many of them are parasitic
  4. They have no chlorophyll


These are unicellular and prokaryotic.

Reason — Bacteria are single-celled organisms that lack a nucleus and membrane-bound organelles. Unlike plants, which are multicellular and have eukaryotic cells, bacteria are classified as prokaryotes. This fundamental difference in cellular structure and organization led to their separation from the plant kingdom.

Question 2

A particular species of which one of the following, is the source bacterium of the antibiotic, discovered next to penicillin, for the treatment of tuberculosis?

  1. Escherichia
  2. Streptomyces
  3. Rhizobium
  4. Nitrobacter



Reason — Streptomycin was discovered next to penicillin by Selman Waksman. It was derived from Streptomyces griseus.

Question 3

Which bacteria is rod shaped?

  1. Coccus
  2. Spirillum
  3. Bacillus
  4. Vibrio



Reason — Rod-shaped bacteria are called bacillus.

Question 4

Which bacteria fixes nitrogen in the soil?

  1. Nitrobacter
  2. Nitrosomonas
  3. Rhizobium
  4. Clostridium



Reason — Rhizobium is the nitrogen fixing bacteria present in root nodules of legumes.

Question 5

Cell wall of bacteria is composed of:

  1. Cellulose
  2. Peptidoglycan
  3. Glycogen
  4. Lipoproteins



Reason — The bacterial cell wall is made up of Peptidoglycan and not cellulose as in plants.

Question 6

Which of the following structures is suspended in the cytoplasm of a bacterial cell ?

  1. Plasma
  2. Capsule
  3. Plasmid
  4. Flagellum



Reason — Plasmid is a small circular DNA suspended in the Cytoplasm.

Question 7

Bacteria mainly reproduces by means of :

  1. Multiple fission
  2. Budding
  3. Binary fission
  4. Regeneration


Binary fission

Reason — Bacteria divides into two by simple cell division. This is known as binary fission.

Question 8

Bacteria are referred to as prokaryotes because:

  1. They have no chlorophyll
  2. They are unicellular
  3. They are free living-
  4. They do not have a well defined nucleus enclosed in a nuclear membrane.


They do not have a well defined nucleus enclosed in a nuclear membrane.

Reason — The cells in which the nuclear membrane is absent is called prokaryotes.

Question 9

Which of the following diseases can be prevented by TAB?

  1. Tuberculosis
  2. Typhoid
  3. Tetanus
  4. Taeniasis



Reason — TAB is the vaccine of Typhoid. It contains killed typhoid bacteria.

Question 10

A preparation consisting of weakened or dead germ substances is:

  1. Toxins
  2. Antitoxins
  3. Toxoids
  4. Vaccines



Reason — Vaccine consists of weakened or dead germ substances. Administration of vaccine results in resistance in body against the particular disease.

Very Short Answer Type

Question 1

Name the following:

(a) The locomotory structure of a bacterium that enables it to swim.

(b) The process of flavouring tea by certain bacteria.

(c) The process of making leather from the animals skin.

(d) Bacterial disease of mustard.

(e) The scientist who discovered the antibiotic streptomycin.


(a) Flagella

(b) Curing

(c) Leather tanning

(d) Black rot of mustard

(e) Selman Waksman

Question 2

Match the items in Column A with those in Column B

Column AColumn B
PenicilliumBacteria occurring in chains.
StreptococciBacteria occurring in pairs.


Column AColumn B
DiplococciBacteria occurring in pairs.
StreptococciBacteria occurring in chains.

Question 3

Fill in the blanks:

(a) The first antibiotic penicillin was discovered by ............... .

(b) ............... bacteria is found living in the nodules on the roots of leguminous plants.

(c) The hormone ............... was the first substance produced by Escherichia coli.

(d) ............... is an example of denitrifying bacteria.

(e) ............... and ............... are the two heterotrophic modes of nutrition in bacteria.


(a) The first antibiotic penicillin was discovered by Alexander Fleming.

(b) Rhizobium bacteria is found living in the nodules on the roots of leguminous plants.

(c) The hormone insulin was the first substance produced by Escherichia coli.

(d) Pseudomonas is an example of denitrifying bacteria.

(e) Saprotrophic and parasitic are the two heterotrophic modes of nutrition in bacteria.

Question 4

Name the bacteria that converts

(a) ammonium compounds to nitrites

(b) nitrites to nitrates


(a) Nitrosomonas

(b) Nitrobacter

Short Answer Type

Question 1

In what form bacteria may be present in the air?


In air, bacteria can be present in the form of spores.

Question 2

Why is spore formation in bacteria not considered a form of reproduction?


Spore formation in bacteria cannot be considered as a form of reproduction as they can reproduce through asexual means only such as cell division or fission. The formation of spores in bacteria is only an escape tactic from unfavorable condition that is exhibited by them.

Question 3

In what respect do you consider bacteria as simple organisms?


Bacteria are unicellular organisms that lack membrane bound cell organelles like chloroplast, mitochondria, etc. and even a well-defined nucleus is absent which states that they have a simpler cellular organization.

Question 4

Define the terms :

(a) Antibiotics

(b) Antitoxins

(c) Serum

(d) Botulism

(e) Pasteurization


(a) Antibiotics — An antibiotic is a chemical substance produced by a living microorganism which can stop the growth of or kill some disease-producing bacteria and fungi.

(b) Antitoxins — Antitoxin is a substance produced in animal bodies which reacts with the poison (toxin) produced by the invading germs.

(c) Serum — Serum actually means blood plasma from which fibrinogen has been removed. It may contain numerous chemical substances including anti-bodies and antitoxins.

(d) Botulism — Botulism is a very serious food poisoning due to a special bacterium sometimes found in tinned or sealed foods.

(e) Pasteurization — Pasteurization is the process of food preservation, applied usually to milk. In this process, the milk is heated at 60°C for 30 minutes and then chilled quickly. It kills majority of bacteria.

Question 5

Give two examples of each :

(a) Bacterial diseases of cattle

(b) Bacterial diseases in plants

(c) Bacterial diseases in humans

(d) Nitrifying bacteria

(e) Free living nitrogen-fixing bacteria found in soil


(a) Anthrax and Bovine tuberculosis

(b) Bacterial blight of cowpea and Black rot of mustard

(c) Cholera and Tuberculosis

(d) Nitrosomonas and Nitrobacter

(e) Azotobacter and Clostridium

Question 6

Write the full forms of the following abbreviations:

(a) TAB

(b) BCG

(c) DNA

(d) GMO


(a) TAB — Typhoid-paratyphoid A and B

(b) BCG — Bacille Calmette-Guerin

(c) DNA — Deoxyribonucleic Acid

(d) GMO — Genetically Modified Organism

Question 7

Give reasons :

(a) Every room in the house should get direct sunlight at least for a short time.

(b) Tinned and sealed food is not always safe to eat.


(a) Direct sunlight contains ultraviolet radiations of the Sun, which help in killing of mould spores present in air. Hence, it is advised that every living room in the house should get direct sunlight at least for a short time.

(b) No, tinned and sealed food are not always safe to eat as it may contain harmful bacteria like Clostridium botulinum that causes food poisoning. Clostridium botulinum releases toxins under low-oxygen conditions. These toxins are very lethal and can block nerve functions leading to muscular and respiratory paralysis.
Moreover, the chemicals used in the inner coating of the container can be harmful for humans.

Question 8

State the differences between:

(a) Decay and putrefaction.

(b) Pasteurization and sterilization of food/objects/equipments.


(a) Difference between Decay and Putrefaction:

Complete breakdown of organic matter by bacteria.Incomplete breakdown of organic matter by bacteria.
Does not emit a foul smell.Emits a foul smell.

(b) Difference between Pasteurization and Sterilization:

Temperature - 60°CTemperature - 110°C
Does not kill sporesKills even spores
Partial sterilizationComplete sterilization
Example – Milk sterilizationExample – Canned food sterilization.

Question 9

Would there be any bacteria in an aquarium?


Yes, bacteria can exist in aquarium. Bacteria can exist practically everywhere, as they can withstand any climatic condition.

Long Answer Type

Question 1

How do bacteria obtain their nourishment?


Most bacteria are heterotrophic i.e. they depend on ready-made food from different sources. In this category, the bacteria maybe:

  1. Saprophytic — Such bacteria draw nourishment from decaying dead organisms.
  2. Parasitic — Such bacteria draw nourishment from the body of their living hosts.

The bacteria secrete powerful enzymes from their cells into the surrounding food containing material. The enzymes make the food material soluble which is then absorbed as a solution into the bacterial cell.

Question 2

Describe any two uses of bacteria in industry.


Uses of bacteria in industry:

  1. Tanning of leather — It is brought about by sunlight with the involvement of a few bacteria which breakdown the soft perishable parts of the skin.
  2. Tea curing — Different flavours of tea are produced by certain bacteria.

Question 3

What are antibiotics? Name any two examples.


Antibiotics are chemical substances produced by a living organism which inhibits or kills the growth of micro-organisms that cause the diseases such as fungi and bacteria. Examples of antibiotics are:

  1. Streptomycin
  2. Penicillin

Question 4

Briefly describe how nitrogen of the atmosphere is converted to nitrates by leguminous plants.


A special category of soil bacteria (Rhizobium) is found living in small nodules on the roots of leguminous plants. These bacteria pick up free nitrogen from the soil and atmosphere and convert it into soluble nitrates. These nitrates are used by the host plant and also by other plants sown later in the same soil.

Question 5

State how the nitrates in the soil get converted to nitrogen of the atmosphere.


Denitrifying bacteria in the soil break down nitrates present in the soil to release nitrogen gas which enters the atmosphere. Pseudomonas is an example of denitrifying bacteria.

Structured / Application / Skill Type

Question 1

Draw a diagram showing the Nitrogen cycle and answer the following questions.

(a) Define the terms:

  1. Nitrification
  2. Denitrification

(b) Distinguish between biological nitrogen fixation and industrial nitrogen fixation.

(c) Name the kind of relationship that exists between Rhizobium and leguminous plants.


(a) Below diagram shows the Nitrogen cycle:

Draw a diagram showing the Nitrogen cycle. Bacteria Economic Importance, Concise Biology Solutions ICSE Class 9.
  1. Nitrification — The conversion of atmospheric nitrogen to nitrates is called nitrification.
  2. Denitrification — The conversion of nitrates into atmospheric nitrogen is called Denitrification.

(b) Difference between biological nitrogen fixation and industrial nitrogen fixation are:

Biological Nitrogen
Industrial Nitrogen
1.Biological nitrogen fixation is carried out primarily by bacteria known as nitrogen-fixing bacteria.Industrial nitrogen fixation involves a series of controlled chemical reactions.
2.Biological nitrogen fixation occurs in natural ecosystems such as soil, aquatic environments and symbiotic associations with plants.Industrial nitrogen fixation occurs in controlled industrial settings, such as chemical plants or fertilizer production facilities.
3.Nitrogen-fixing bacteria possess the enzyme nitrogenase, which converts atmospheric nitrogen (N2) into ammonia (NH3) through a series of biochemical reactions.The Haber-Bosch process uses high pressure and temperature, along with a catalyst, to convert atmospheric nitrogen (N2) and hydrogen (H2) into ammonia (NH3).

(c) Symbiotic relationship.

Question 2

Would there be any bacteria in an aquarium ?

Would there be any bacteria in an a aquarium ? Bacteria Economic Importance, Concise Biology Solutions ICSE Class 9.

(a) A balanced aquarium contains certain animals as well as some plants. How many kinds of animals can you make out in the aquarium shown here. Name any two such animals.

(b) Do you think there would be some bacteria in it? If so in which part of the aquarium would they be occurring in abundance and what for?


(a) Fishes and snails are present in the aquarium shown here.

(b) Yes, aquariums contain bacteria. A balanced aquarium contains some nitrifying bacteria like Nitrosomonas and Nitrobacter which converts the ammoniacal waste released by fish to nitrates. The filter media and various solid surfaces in the aquarium, such as gravel, rocks, plants, and decorations, harbor these bacteria in abundance.