c.
d.
Type strain is used for referring to?
a) species
Microbiology MCQs
9. Which of the following is diagnosed by serologic means?
a.
b.
c.
d.
1. Which of these bacterial components is least likely to
contain useful antigens?
a.
b.
c.
d.
Cell wall
Flagella
Ribosomes
Capsule
Mycoplasmas
Amoeba
E.coli
Spheroplast
10. Diarrhoea is not caused by
a.
b.
c.
d.
a.
b.
c.
d.
3. The association of endotoxin in gram-negative bacteria is
due to the presence of
Steroids
Peptidoglycan
Lipopolysaccharides
Polypeptide
Contains metabolic enzymes
Is selectively permeable
Regulates the entry and exit of materials
Contains proteins and phospholipids
a.
b.
c.
d.
b.
c.
d.
Mycobacterium tuberculosis stains blue because of the
thick lipid layer
Streptococcus pyogenes stains blue because of a thick
peptidoglycan layer
Escherichia coli stains pink because of a thin
peptidoglycan layer
Mycoplasma pneumoniae is not visible in the Gram’s stain
because it has no cell wall
13. The bacterial genus where sterols are present in the cell
membrane is
a.
b.
c.
d.
a.
b.
c.
d.
Vibrio
Mycoplasma
Escherichia
Chlamydia
14. The bacterium that infects other gram-negative bacteria is
a.
b.
c.
d.
Also Read: Gram positive and gram negative bacteria
6. Which of the following is not a recognised cause of
diarrhoea?
Their cell wall is composed of peptidoglycan
They are selectively permeable
They contain osmoregulating porins
They block water molecules from entering the cell
Also Read: Prokaryotic cells
5. Which of the statements regarding gram staining is wrong?
a.
Staphylococcus aureus from Staphylococcus epidermidis
Staphylococcus epidermidis from Neisseria meningitidis
Streptococcus pyogenes from Enterococcus faecalis
Streptococcus pyogenes from Staphylococcus aureus
12. Prokaryotic cells are more resistant to osmotic shock than
eukaryotic cells because
4. The prokaryotic cell membrane
a.
b.
c.
d.
Shigella dysenteriae
Streptococcus pyogenes
Clostridium difficile
Salmonella enteriditis
11. The coagulase is done to differentiate
Also Read: Microbiology
a.
b.
c.
d.
Actinomycosis
Q-fever
Pulmonary tuberculosis
Gonorrhea
Also Read: Bacteria
2. Which of the following contains structures composed of Nacetylmuramic acid and N- acetylglucosamine?
a.
b.
c.
d.
Klebsiella pneumoniae
Bacteroides fragilis
Proteus mirabilis
Haemophilus influenza
Bdellovibrio
Pseudomonas putida
15. Which phage is used for phage display technique?
a.
b.
c.
d.
Vibrio cholerae
Escherichia coli
Clostridium perfringens
Enterococcus faecalis
T7
M13
ƛ-phage
ɸ6
Also Read: Eukaryotic cells
7. Which of the following is a gram-positive eubacterium?
a.
b.
c.
d.
Actinomyces
Clostridium
Rhizobium
Clostridium, Actinomyces
8. Which of the following microorganisms is not responsible
for urinary tract infection?
a.
b.
Proteus mirabilis
Escherichia coli
Answer Key
1- c
2- c
3- c
4- d
5- a
6- d
7- d
8- d
9- b
10- b
11- a
12- a
13- b
14- c
15- b
Microbiology is the study of a variety of living organisms which are
invisible to the naked eye like bacteria and fungi and many other
microscopic organisms. Although tiny in size these organisms form
the basis for all life on earth. These microbes as they are also
known to produce the soil in which plants grow and the fix
atmospheric gases that both plants animals use. About 3 billion
years ago at the time of formation of the earth, microbes were the
only lives on earth. Microorganisms have played a key role in the
evolution of the planet earth.
The lineage of life on Earth originated from these microbes:
Microorganisms affect animals, the environment, the food supply
and also the healthcare industry. There are many different areas of
microbiology including environmental, veterinary, food,
pharmaceutical and medical microbiology, which is the most
prominent.
Branches of microbiology
Microorganisms are very important to the environment, human
health and the economy. Few have immense beneficial effects
without which we could not exist. Others are really harmful, and our
effort to overcome their effects tests our understanding and skills.
Certain microorganisms can be beneficial or harmful depending on
what we require from them.
2.Mycology –The study of fungi
Harmful Microorganisms
Disease and decay are neither inherent properties of organic
objects, nor are caused by physical damage, it is microorganisms
that bring about these changes. We are surrounded by
bacteria, virus, and fungi. Many microorganisms cause diseases in
cattle, crops and others are known for entering human bodies and
causing various diseases.
Examples of familiar human diseases are:
Bacteria: pneumonia, bacterial dysentery, diphtheria, bubonic
plague, meningitis, typhoid, cholera, salmonella, meningococcal
Virus: Chickenpox, measles, mumps, German measles, colds,
warts, cold sores, influenza
Protozoa: amoebic dysentery, malaria,
Fungi: ringworm, athlete’s foot
Useful-Microorganisms
As decomposers, bacteria and fungi play an important role in an
ecosystem. They break down dead or waste organic matter and
release inorganic molecules. Green plants take these nutrients
which are in turn consumed by animals, and the products of these
plants and animals are again broken down by decomposers.
Yeast is a single-celled fungus that lives naturally on the surface of
the fruit. It is economically important in bread-making and brewing
beer and also in the making of yoghurt.
Most microorganisms are unicellular; if they are multicellular, they
lack highly differentiated tissues.
There fundamentally two different types of cells, One being
Prokaryotic and the other Eukaryotic
1.Bacteria
2.Archaea
3.Eucarya
There are various different branches in microbiology and these
include the following:
1.Bacteriology- The study of bacteria
3.Phycology- The study of photosynthetic eukaryotes. (AlgaeSeaweed)
4.Protozoology – The study of protozoa (Single-celled eukaryotes)
5.Virology- The study of viruses, non-cellular particles which
parasitize cells.
6.Parasitology- The study of parasites which include pathogenic
protozoa certain insects and helminth worms.
7.Nematology- The study of nematodes.
Eukaryotic Cell Definition
“Eukaryotic cells are the cells that contain a
membrane bound nucleus and organelles.”
Table of Contents

Explanation

Characteristics

Structure

Diagram

Cell Cycle

Examples
What is a Eukaryotic Cell?
Eukaryotic cells have a nucleus enclosed within the nuclear
membrane and form large and complex organisms. Protozoa, fungi,
plants, and animals all have eukaryotic cells. They are classified
under the kingdom Eukaryota.
They can maintain different environments in a single cell that allows
them to carry out various metabolic reactions. This helps them grow
many times larger than the prokaryotic cells.
Also refer: Difference between Prokaryotic and Eukaryotic Cells
Characteristics of Eukaryotic Cells
The features of eukaryotic cells are as follows:
1. Eukaryotic cells have the nucleus
enclosed within the nuclear membrane.
2.
The cell has mitochondria.
3. Flagella and cilia are the locomotory
organs in a eukaryotic cell.
4. A cell wall is the outermost layer of the
eukaryotic cells.
5. The cells divide by a process called
mitosis.
Microbes especially prokaryotes are numerous in number in
comparison to eukaryotes.
6.
The eukaryotic cells contain a cytoskeletal structure.
7.
The nucleus contains a single, linear DNA, which carries all These are the main site for protein synthesis and are composed of
the genetic information.
proteins and ribonucleic acids.
Structure Of Eukaryotic Cell
The eukaryotic cell structure comprises the following:
Plasma Membrane

The plasma membrane separates the cell from the outside
environment.

It comprises specific embedded proteins, which help in the
exchange of substances in and out of the cell.
Cell Wall

A cell wall is a rigid structure present outside the plant cell.
It is, however, absent in animal cells.

It provides shape to the cell and helps in cell-to-cell
interaction.

It is a protective layer that protects the cell from any injury
or pathogen attacks.

It is composed of cellulose, hemicellulose, pectins,
proteins, etc.
Also refer: Cell Wall
Mitochondria

These are also known as “powerhouse of cells” because
they produce energy.

It consists of an outer membrane and an inner membrane.
The inner membrane is divided into folds called cristae.

They help in the regulation of cell metabolism.
Lysosomes
They are known as “suicidal bags” because they possess hydrolytic
enzymes to digest protein, lipids, carbohydrates, and nucleic acids.
Plastids
These are double-membraned structures and are found only
in plant cells. These are of three types:

Chloroplast that contains chlorophyll and is involved in
photosynthesis.

Chromoplast that contains a pigment called carotene that
provides the plants yellow, red, or orange colours.

Leucoplasts that are colourless and store oil, fats,
carbohydrates, or proteins.
Cytoskeleton
The cytoskeleton is present inside the cytoplasm, which consists of
microfilaments, microtubules, and fibres to provide perfect shape to
the cell, anchor the organelles, and stimulate the cell movement.
Endoplasmic Reticulum
It is a network of small, tubular structures that divides the cell
surface into two parts: luminal and extraluminal.
Endoplasmic Reticulum is of two types:

Rough Endoplasmic Reticulum contains ribosomes.

Smooth Endoplasmic Reticulum that lacks ribosomes and
is therefore smooth.
Nucleus
Eukaryotic Cell Diagram
Eukaryotic cell diagram mentioned below depicts different cell
organelles present in eukaryotic cells. The nucleus, endoplasmic
reticulum, cytoplasm, mitochondria, ribosomes, lysosomes are
clearly mentioned in the diagram.
Explore more about Cell organelles
Eukaryotic Cell Diagram illustrated above shows the presence of a
true nucleus.
Eukaryotic Cell Cycle
The eukaryotic cells divide during the cell cycle. The cell passes
through different stages during the cycle. There are various
checkpoints between each stage.

The nucleoplasm enclosed within the nucleus contains
DNA and proteins.
Quiescence (G0)

The nuclear envelop consists of two layers- the outer
membrane and the inner membrane. Both the membranes
are permeable to ions, molecules, and RNA material.

Ribosome production also takes place inside the nucleus.
This is known as the resting phase, and the cell does not divide
during this stage. The cell cycle starts at this stage. The cells of the
liver, kidney, neurons, and stomach all reach this stage and can
remain there for longer periods. Many cells do not enter this stage
and divide indefinitely throughout their lives.
Golgi Apparatus
Interphase
In this stage, the cells grow and take in nutrients to prepare them for
the division. It consists of three

It is made up of flat disc-shaped structures called
cisternae.

It is absent in red blood cells of humans and sieve cells of
plants.
checkpoints:

They are arranged parallel and concentrically near the
nucleus.
Synthesis (S) – DNA replication takes place in this phase.

It is an important site for the formation of glycoproteins and
glycolipids.
Also read: Golgi Apparatus
Gap 1 (G1) – Here the cell enlarges. The proteins also increase.
Gap 2 (G2) – Ther cells enlarge further to undergo mitotic division.
Mitosis
Mitosis involves the following stages:
Ribosomes

Prophase
Are viruses eukaryotes?

Prometaphase

Metaphase
Viruses are neither eukaryotes nor prokaryotes. Since viruses are a
link between living and non-living they are not considered in either
category.

Anaphase

Telophase

Cytokinesis
On division, each daughter cell is an exact replica of the original
cell.
Examples of Eukaryotic Cells
Eukaryotic cells are exclusively found in plants, animals, fungi,
protozoa, and other complex organisms. The examples of
eukaryotic cells are mentioned below:
Plant Cells
The cell wall is made up of cellulose, which provides support to the
plant. It has a large vacuole which maintains the turgor pressure.
The plant cell contains chloroplast, which aids in the process of
photosynthesis.
Fungal Cells
The cell wall is made of chitin. Some fungi have holes known as
septa which allow the organelles and cytoplasm to pass through
them.
Animal Cells
What are the salient features of a eukaryotic cell?
A eukaryotic cell has the following important features:

A eukaryotic cell has a nuclear membrane.

It has mitochondria, Golgi bodies, cell wall.

It also contains locomotory organs such as cilia and
flagella.

The nucleus has a DNA that carries all the genetic
information.
How does a eukaryotic cell divide?
A eukaryotic cell divides by the process of mitosis. It undergoes the
following stages during cell division:

Prophase

Metaphase

Anaphase

Telophase

Cytokinesis
When did the first eukaryotic cell evolve?
These do not have cell walls. Instead, they have a cell membrane.
That is why animals have varied shapes. They have the ability to
perform phagocytosis and pinocytosis.
The first eukaryotic cells evolved about 2 billion years ago. This is
explained by the endosymbiotic theory that explains the origin of
eukaryotic cells by the prokaryotic organisms. Mitochondria and
chloroplasts are believed to have evolved from symbiotic bacteria.
Protozoa
What is the evidence for endosymbiotic theory?
Protozoans are unicellular organisms. Some protozoa have cilia for
locomotion. A thin layer called pellicle provides supports to the cell.
The first evidence in support of the endosymbiotic theory is that
mitochondria and chloroplast have their own DNA and this DNA is
similar to the bacterial DNA. The organelles use their DNA to
produce several proteins and enzymes to carry out certain activities.
For more information on Eukaryotic Cells, its definition,
characteristics, structure, and examples, keep visiting BYJU’S
website or download BYJU’S app for further reference.
Related Links
Prokaryotic and Eukaryotic Cells
Difference between the Plant cell and Animal cell
Frequently Asked Questions
Are eukaryotic cells unicellular or multicellular?
Eukaryotic cells may be unicellular or multicellular. Paramecium,
Euglena, Trypanosoma, Dinoflagellates are unicellular eukaryotes.
Plants and animals are multicellular eukaryotes.
What is the most important characteristic of
eukaryotic cells that distinguishes it from prokaryotic
cells?
Eukaryotic cells have a membrane-bound nucleus. On the contrary,
prokaryotic cells lack a true nucleus, i.e., they have no nuclear
membrane. Unlike eukaryotic cells, the prokaryotic cells do not have
mitochondria, chloroplast and endoplasmic reticulum.
Prokaryotic Cell Definition
“Prokaryotic cells are the cells that do not have a
true nucleus and membrane-bound organelles.”
Table of Contents

Explanation

Characteristics

Structure

Diagram

Components

Reproduction

Examples
Prokaryotic Cell Diagram
The prokaryotic cell diagram given below represents a bacterial cell.
It depicts the absence of a true nucleus and the presence of a
flagellum that differentiates it from a eukaryotic cell.
Prokaryotic Cell Diagram illustrates the absence of a true nucleus
What is a Prokaryotic Cell?
Components of Prokaryotic Cells
Prokaryotic cells are single-celled microorganisms known to be the
earliest on earth. Prokaryotes include Bacteria and Archaea. The
photosynthetic prokaryotes include cyanobacteria that perform
photosynthesis.
The prokaryotic cells have four main components:
Plasma Membrane- It is an outer protective covering of
phospholipid molecules which separates the cell from the
surrounding environment.
A prokaryotic cell consists of a single membrane and therefore, all
the reactions occur within the cytoplasm. They can be free-living or
parasites.
Cytoplasm- It is a jelly-like substance present inside the cell. All the
cell organelles are suspended in it.
Characteristics of Prokaryotic Cell
DNA- It is the genetic material of the cell. All the prokaryotes
possess a circular DNA. It directs what proteins the cell creates. It
also regulates the actions of the cell.
Prokaryotic cells have different characteristic features. The
characteristics of the prokaryotic cells are mentioned below.
Ribosomes- Protein synthesis occurs here.
1.
They lack a nuclear membrane.
2.
Mitochondria, Golgi bodies, chloroplast, and lysosomes are
absent.
3.
The genetic material is present on a single chromosome.
4.
The histone proteins, the important constituents of
eukaryotic chromosomes, are lacking in them.
5.
The cell wall is made up of carbohydrates and amino acids.
6.
The plasma membrane acts as the mitochondrial
membrane carrying respiratory enzymes.
7.
They divide asexually by binary fission. The sexual mode
of reproduction involves conjugation.
Some prokaryotic cells possess cilia and flagella which helps in
Prokaryotic Cell Structure
A prokaryotic cell does not have a nuclear membrane. However,
the genetic material is present in a region in the cytoplasm known
as the nucleoid. They may be spherical, rod-shaped, or spiral. A
prokaryotic cell structure is as follows:
1.
Capsule– It is an outer protective covering found in the
bacterial cells, in addition to the cell wall. It helps in
moisture retention, protects the cell when engulfed, and
helps in the attachment of cells to nutrients and surfaces.
2.
Cell Wall– It is the outermost layer of the cell which gives
shape to the cell.
3.
Cytoplasm– The cytoplasm is mainly composed of
enzymes, salts, cell organelles and is a gel-like
component.
locomotion.
Reproduction in Prokaryotes
A prokaryote reproduces in two ways:

Asexually by binary fission

Sexually by conjugation
Binary Fission
1.
The DNA of an organism replicates and the new copies
attach to the cell membrane.
4.
Cell Membrane– This layer surrounds the cytoplasm and
regulates the entry and exit of substances in the cells.
2.
The cell wall starts increasing in size and starts moving
inwards.
5.
Pili– These are hair-like outgrowths that attach to the
surface of other bacterial cells.
3.
A cell wall is then formed between each DNA, dividing the
cell into two daughter cells.
6.
Flagella– These are long structures in the form of a whip,
that help in the locomotion of a cell.
7.
Ribosomes– These are involved in protein synthesis.
8.
Plasmids– Plasmids are non-chromosomal DNA
structures. These are not involved in reproduction.
9.
Nucleoid Region– It is the region in the cytoplasm where
the genetic material is present.
A prokaryotic cell lacks certain organelles like mitochondria,
endoplasmic reticulum, and Golgi bodies.
Recombination
In this process, genes from one bacteria are transferred to the
genome of other bacteria. It takes place in three ways-conjugation,
transformation, transduction.

Conjugation is the process in which genes are transferred
between two bacteria through a protein tube structure
called a pilus.

Transformation is the mode of sexual reproduction in
which the DNA from the surroundings is taken by the
bacterial cell and incorporated in its DNA.
How is the prokaryotic cell structure different from
that of the eukaryotic cell?

Transduction is the process in which the genetic material
is transferred into the bacterial cell with the help of viruses.
Bacteriophages are the virus that initiates the process.
Prokaryotic cells lack a true nucleus. The nucleus is devoid of the
nuclear membrane. On the contrary, the nucleus of the eukaryotic
cells is enclosed by a nuclear membrane. A prokaryotic cell also
lacks mitochondria and chloroplast, unlike a eukaryotic cell.
Examples of Prokaryotic Cells
The examples of the prokaryotic cells are mentioned below:
Bacterial Cells
These are unicellular organisms found everywhere on earth from
soil to the human body.
They have different shapes and structures.
How does a prokaryotic cell divide?
Prokaryotic cells undergo asexual reproduction. Most prokaryotic
cells divide by binary fission, where the cells divide into two
daughter cells.
Why is the process of cell division in prokaryotic
cells different from that in eukaryotes?
Prokaryotic cells are simpler than eukaryotic cells. They do not have
The cell wall is composed of peptidoglycan that provides structure to
a nuclear membrane surrounding their DNA, therefore, cell division
the cell wall.
is different than that in eukaryotes.
Bacteria have some unique structures such as pili, flagella and
capsule.
When did the prokaryotic cells evolve?
They also possess extrachromosomal DNA known as plasmids.
They have the ability to form tough, dormant structures known as
endospores that helps them to survive under unfavourable
conditions. The endospores become active when the conditions are
favourable again.
Archaeal Cells
Archaebacteria are unicellular organisms similar to bacteria in
shape and size.
They are found in extreme environments such as hot springs and
other places such as soil, marshes, and even inside humans.
They have a cell wall and flagella. The cell wall of archaea does not
contain peptidoglycan.
The membranes of the archaea have different lipids with a
completely different stereochemistry.
Just like bacteria, archaea have one circular chromosome. They
also possess plasmids.
For more information on Prokaryotic Cells, its definition, structure,
characteristics and examples, keep visiting BYJU’S Biology website
or download BYJU’S app for further reference.
Related Links
Difference between a prokaryotic cell and eukaryotic cell
Difference between an archaea and bacteria
Frequently Asked Questions
What are the structural features of prokaryotic cells?
The prokaryotic cell structure is composed of:

Cell wall

Cell membrane

Capsule

Pili

Flagella

Ribosomes

Plasmids
The first prokaryotic cells evolved around 3.5 billion years ago. The
eukaryotic cells were formed after the prokaryotic cells and are
believed to have evolved from them.
Bacteria
One of the very first organisms to evolve on earth was
probably a unicellular organism, similar to modern
bacteria. Ever since then, life has evolved into a
multitude of life forms over many millennia. However,
we can still trace our ancestry back to this single-celled
organism.
Table of Contents


Definition
Diagram

Structure

Classification

Reproduction

Useful Bacteria

Harmful Bacteria
Today, bacteria are considered as one of the oldest
forms of life on earth. Even though most bacteria make
us ill, they have a long-term, mutual relationship with
humans and are very much important for our survival.
But before we elaborate on its uses, let us know the
structure of bacteria, its classification, and the bacteria
diagram in detail.
Bacteria Definition
“Bacteria are unicellular organisms belonging to the
prokaryotic group where the organisms lack a few
organelles and a true nucleus”.
Also Read: Gram Negative Bacteria
Bacteria Diagram
The bacteria diagram given below represents the
Bacteria can be classified into various categories based
structure of bacteria with its different parts. The cell
on their features and characteristics. The classification
wall, plasmid, cytoplasm and flagella are clearly marked of bacteria is mainly based on the following:
in the diagram.

Shape

Composition of the cell wall

Mode of respiration

Mode of nutrition
Classification of bacteria based on Shape
Bacteria Diagram representing the Structure of Bacteria
Type of Classification
Examples
Bacillus (Rod-shaped)
Escherichia coli (E. coli)
Spirilla or spirochete (Spiral)
Spirillum volutans
Coccus (Sphere)
Streptococcus pneumoniae
Vibrio (Comma-shaped)
Vibrio cholerae
Structure of Bacteria
The structure of bacteria is known for its simple body
design. Bacteria are single-celled microorganisms with
the absence of the nucleus and other cell organelles;
hence, they are classified as prokaryotic organisms.
They are also very versatile organisms, surviving in
extremely inhospitable conditions. Such organisms are
called extremophiles. Extremophiles are further
categorized into various types based on the types of
environments they inhabit:
1.
2.
3.
4.
5.
6.
Thermophiles
Acidophiles
Alkaliphiles
Osmophiles
Barophiles
Cryophiles
Another fascinating feature of bacteria is their
protective cell wall, which is made up of a special
protein called peptidoglycan. This particular protein
isn’t found anywhere else in nature except in the cell
walls of bacteria.
Classification of bacteria based on the Composition of
the Cell Wall
Type of Classification
Examples
Peptidoglycan cell wall
Gram-positive bacteria
Lipopolysaccharide cell
wall
Gram-negative bacteria
Classification of bacteria based on the Mode of
Nutrition
Type of Classification
But few of them are devoid of this cell wall, and others
have a third protection layer called capsule. On the outer
layer, one or more flagella or pili is attached, and it
Autotrophic Bacteria
functions as a locomotory organ. Pili can also help
certain bacteria to attach themselves to the host’s cells.
Heterotrophic Bacteria
They do not contain any cell organelle as in animal or
plant cell except for ribosomes.
Examples
Cyanobacteria
All disease-causing bacteria
Ribosomes are the sites of protein synthesis. In addition Classification of bacteria based on the Mode of
to this DNA, they have an extra circular DNA called
Respiration
plasmid. These plasmids make some strains of bacteria
resistant to antibiotics.
Type of Classification
Examples
Also Read: Gram Positive Bacteria
Classification of Bacteria
Anaerobic Bacteria
Actinomyces
Aerobic Bacteria
Mycobacterium
Also Read: Difference between Bacteria and Virus
Reproduction in Bacteria
4. Production of antibiotics, which is used in the
treatment and prevention of bacterial infections –
Soil bacteria
Also Refer: Antibiotics
Harmful Bacteria
There are bacteria that can cause a multitude of
illnesses. They are responsible for many of
the infectious diseases like pneumonia, tuberculosis,
diphtheria, syphilis, tooth decay. Their effects can be
rectified by taking antibiotics and prescribed
medication.
However, precaution is much more effective. Most of
these disease-causing bacteria can be eliminated
by sterilizing or disinfecting exposed surfaces,
instruments, tools and other utilities. These methods
include- application of heat, disinfectants, UV
radiations, pasteurization, boiling, etc.
Bacteria follow an asexual mode of
reproduction, called binary fission. A single bacterium
divides into two daughter cells. These are identical to
the parent cell as well as to each other. Replication of
DNA within parent bacterium marks the beginning of
the fission. Eventually, cell elongates to form two
daughter cells.
The rate and timing of reproduction depend upon the
conditions like temperature and availability of nutrients.
When there is a favourable condition, E.coli or
Escherichia coli produces about 2 million bacteria every
7 hours.
Bacterial reproduction is strictly asexual, but it can
undergo sexual reproduction in very rare cases.
Genetic recombination in bacteria has the potential to
occur through conjugation, transformation, or
transduction. In such cases, the bacteria may become
resistant to antibiotics since there is variation in the
genetic material (as opposed to asexual reproduction
where the same genetic material is present in
generations)
Also Read:

Cryptobiosis

Microorganisms: Friend And Foe

Biology
Frequently Asked Questions
1. What are the different types of bacteria??
Bacteria can be divided into several types based on
several characteristics such as shape, cell wall
composition, mode of respiration, and mode of
nutrition.
2. What is bacteria? How do you define bacteria?
Bacteria are prokaryotic unicellular organisms. They
have a relatively simple cell structure compared to
eukaryotic cells. They also do not possess any
membrane-bound organelles such as a nucleus.
However, do they possess genetic material (DNA or
RNA) in the intracellular space called the nucleoid
Also Read: Binary fission
3. How do bacteria reproduce?
Useful Bacteria
Bacteria reproduce through a process called binary
fission. In this process, a single bacterium divides into
two daughter cells. These daughter cells are identical to
the parent cell as well as to each other.
Not all bacteria are harmful to humans. There are some
bacteria which are beneficial in different ways. Listed
below are few benefits of bacteria:
1. Convert milk into curd – Lactobacillus or lactic acid
bacteria
2. Ferment food products – Streptococcus and Bacillus
3. Help in digestion and improving the body’s
immunity system – Actinobacteria, Bacteroidetes,
Firmicutes, Proteobacteria
4. State 4 examples of bacteria.

Streptococcus

Bacillus

Actinobacteria

Proteobacteria
Classification of Microorganism
Bacteria
Fungi
Protozoa
Microbes are categorized into four major groups:

Bacteria

Fungi

Algae

Protozoa
Viruses, on the other hand, are microscopic but differ from
microbes. Differ in their reproduction aspects, as they reproduce
only in the cells of their hosts. These host organisms can be of
animals, bacteria or even plants for that matter. A virus is typically
coated by protein and has a nucleic acid molecule.
Useful Microorganisms
Tuberculosis
Ringworm
Malaria
Flu &
Common
cold
Typhoid
Athlete’s foot
Dysentery
Warts
Cholera
Candidiasis
Chagas
disease
Polio
Plague
Tinea
versicolor
Sleeping
sickness
Herpes and
cold sores
Meningitis
Onychomycosis
Intestinal
protozoan
disease
Chickenpox
Following are a few examples of useful microorganisms:

Extensively used in the baking industry to make cakes,
bread, pastry etc.

Used in the production of milk products. Example:
Lactobacillus bacteria is used in the formation of curd from
milk

Since ages, microbes are being used in the production of
alcohol

It is also used to make organic acids. Acids such as citric
acid, lactic acid, fumaric acid, gluconic acids are made
using microbial activity

Used in the production of steroids

Antibiotics are produced using microorganisms

Used in the production of vitamins: Vitamins such as
Vitamin B complex, Riboflavin is produced by Ashbya
gossypii, Eremothecium ashbyii and Clostridium bytyricum.
Ascorbic acid, also known as Vitamin C is produced by
species of Acetobacter

Tetanus
Smallpox
Lyme
disease
Ebola
Diseases Caused by Microorganisms in Animals
Diseases
Microorganism
Anthrax diseases
Bacillus anthracis
Foot and Mouth disease
Virus
Diseases Caused by Microorganisms in Plants
Diseases
Microorganism
Citrus canker
Bacteria
Rust of wheat
Fungi
Yellow vein mosaic of Okra
Virus
Microorganisms synthesize enzymes such as Lipase,
Lactase, Amylase, Pectinase, Penicillinase.

They increase the fertility of the soil and by fixing nitrogen

Help in the treatment of sewage

Extensively used to clean up our environment

Used in pest control
Food Spoilage by Microorganisms
1.
Harmful Microorganisms

The microorganisms that cause diseases in living beings
are known as pathogens.

The pathogens can enter our bodies through air, water and
food.

Some pathogens are transmitted directly from an infected
person.

The diseases which are transmitted by an infected person
directly or indirectly are known as communicable diseases.
For eg., common cold, tuberculosis, etc.
Virus
2.
3.
4.
5.
Food spoilage refers to the damage in the quality of food
that makes it unsuitable for human consumption.
Bacteria, moulds, and yeast are the main causes of food
spoilage.
Moulds spoil food with reduced water activity. For eg., dry
cereals, cereal products.
These microbes produce certain enzymes that decompose
the important constituents of food.
Bacteria, on the other hand, cause the spoilage of food
with increased water activity. For eg., milk products.
Some Interesting Facts About Microbes

Microbes can be fatal.

Microbes in our gut cause change of mood.

Dry hands have fewer bacteria than damp hands.

The smallest known bacteria is the Mycoplasma.
Diseases Caused By Microorganisms

50% of the oxygen we breathe come from microbes.
Some diseases caused by microbes are:

Your belly button alone has more than 1400 bacteria.

Microorganisms also grow on food and spoil it. That is why
preservatives are added in the food to prevent it from
spoilage.

There are more than a billion microbes in a person’s
mouth.

1.82kgs of your body’s weight constitutes the collective
weight of microbes in your body.
This was just a brief about the microorganisms- its beneficial,
harmful and few facts Stay tuned with BYJU’S Biology to learn more
about microorganisms-friend and foe and other related topics.
Diseases Caused By Microorganisms
There are several diseases caused by microorganisms. Let us have
a look at a few of them.

Viral diseases are caused by viruses. These include both
acute and infectious diseases like the common cold, to
chronic disease like AIDS. Apart from these acute
diseases, viruses are also responsible for mumps, polio,
rabies etc.

Diseases caused by bacteria include diphtheria, typhoid,
cholera etc.

Malaria and sleeping sickness are diseases caused by
protozoa.

Worms like roundworms, tapeworms could cause diseases
like Ascariasis and Taeniasis respectively.
German Measles
Rubella
Chickenpox
Varicella zoster
Whooping cough
Bardotella pertussis
Bubonic plague
Yersinia pestis
Ringworm
Trichophyton rubrum
Tuberculosis
Mycobacterium tuberculosis
Malaria
Plasmodium falciparum
Athlete’s foot
Trichophyton mentagrophytes
Who is the father of biology?
Philosopher Aristotle
Who is the mother of biology?
Maria Sibylla Merian
The microorganisms cause diseases in the following ways:
Who first discovered biology?

They reach their target site in the body.

Multiply rapidly.

Attach to the target site to be infected.
Who is the Father of Zoology?

Avoid and survive an attack by the immune system of the
host.
Aristotle

Obtain nutrients from the host.
Who is the Father of Virology?
Microbes and Diseases
Viruses
Viruses can be seen only through an electron microscope. They are
inactive outside a living cell. Once they are inside the host body,
they take over the entire cellular activities of the organism. They
cannot be destroyed by antibiotics. Common cold, measles, mumps,
smallpox are some of the diseases caused by viruses.
Bacteria
Not all bacteria cause diseases. The bacteria that infects an
organism produces toxins that can cause diseases. Cholera,
tuberculosis, anthrax are caused by bacteria. These can be killed by
antibiotics.
Fungi
Thomas Beddoes
Martinus Beijerinck
Difference Between Gram-positive and
Gram-negative Bacteria
Bacteria are a large group of minute, unicellular,
microscopic organisms, which have been classified as
prokaryotic cells, as they lack a true nucleus. These
microscopic organisms comprise a simple physical
structure, including cell wall, capsule, DNA, pili,
flagellum, cytoplasm and ribosomes.
Bacteria can be gram-positive or gram-negative
depending upon the staining methods. Let us have a
detailed look at the difference between the two types of
bacteria.
Fungi can grow in damp, moist areas on the body and lead to
infections such as athlete’s foot, ringworm, etc.
Difference between Gram-Positive and GramNegative Bacteria
Protozoa
Following are the important differences between grampositive and gram-negative bacteria:
Protozoans such as amoeba cause diseases such as amoebic
dysentery. Malaria and sleeping sickness is also caused by
protozoans.
Following is the list of microorganisms and infectious
diseases caused by them:
Diseases
Microorganisms
Cold
Rhinovirus
Mesosome
Difference between Gram-Positive and Gram-Negative Bacteria
It is more prominent.
It is less prominent.
Gram-Negative bacteria
Gram-Positive bacteria
Morphology
Cell Wall
Cocci or spore-forming rods
A single-layered, smooth cell
wall
A double-layered, wavy cellwall
Cell Wall thickness
The thickness of the cell wall is
20 to 80 nanometres
It is a thick layer/ also can be
multilayered
Flagella Structure
Two rings in basal body
The thickness of the cell wall
is 8 to 10 nanometres
Peptidoglycan Layer
Non-spore forming rods.
Four rings in basal body
Lipid content
Very low
20 to 30%
Lipopolysaccharide
It is a thin layer/ often singlelayered.
Absent
Present
Teichoic acids
Toxin Produced
Presence of teichoic acids
Absence of teichoic acids
Exotoxins
Endotoxins or Exotoxins
Outer membrane
Resistance to Antibiotic
The outer membrane is absent
The outer membrane is
present (mostly)
Porins
Absent
More susceptible
More resistant
Examples
Occurs in Outer Membrane
Staphylococcus, Streptococcus,
Escherichia, Salmonella, etc.
etc.
Gram Staining
These bacteria retain the crystal
violet colour even after they are
washed with acetone or alcohol
and appear as purple-coloured
when examined under the
microscope after gram staining.
These bacteria do not retain
the stain colour even after
they are washed with acetone
or alcohol and appear as pinkcoloured when examined
under the microscope after
gram staining.
Gram-Positive and Gram-Negative Bacteria –
Overview
The gram-positive bacteria retain the crystal violet
colour and stains purple whereas the gram-negative
bacteria lose crystal violet and stain red. Thus, the two
types of bacteria are distinguished by gram staining.
Gram-negative bacteria are more resistant against
antibodies because their cell wall is impenetrable.
Gram-positive and gram-negative bacteria are classified
based on their ability to hold the gram stain. The gramnegative bacteria are stained by a counterstain such as
safranin, and they are de-stained because of the alcohol
wash. Hence under a microscope, they are noticeably
pink in colour. Gram-positive bacteria, on the other
hand, retains the gram stain and show a visible violet
colour upon the application of mordant (iodine) and
ethanol (alcohol).
This technique was proposed by Christian Gram to
distinguish the two types of bacteria based on the
difference in their cell wall structures. The grampositive bacteria retain the crystal violet dye, which is
because of their thick layer of peptidoglycan in the cell
wall.
This process distinguishes bacteria by identifying
peptidoglycan that is found in the cell wall of the grampositive bacteria. A very small layer of peptidoglycan is
dissolved in gram-negative bacteria when alcohol is
added.
Difference between Gram-Positive and GramNegative Bacteria – Key Points

The cell wall of gram-positive bacteria is composed
of thick layers peptidoglycan.

The cell wall of gram-negative bacteria is composed
of thin layers of peptidoglycan.

In the gram staining procedure, gram-positive cells
retain the purple coloured stain.

In the gram staining procedure, gram-negative cells
do not retain the purple coloured stain.

Gram-positive bacteria produce exotoxins.

Gram-negative bacteria produce endotoxins.
For more information on the differences between grampositive and gram-negative bacteria, keep visiting
BYJU’S website or download the BYJU’S app for
further reference.
Further Reading:
Gram-positive bacteria constitute a cell wall, which is
 Microorganisms – Useful Or Harmful
mainly composed of multiple layers of peptidoglycan
 Gram-Positive Bacteria
that forms a rigid and thick structure. Its cell wall
additionally has teichoic acids and phosphate. The
Frequently Asked Questions
teichoic acids present in the gram-positive bacteria are
of two types – the lipoteichoic acid and the teichoic wall
Give a few examples of gram-positive bacteria.
acid. The cell wall is known as murein.
In gram-negative bacteria, the cell wall is made up of an Gram-positive bacteria include the bacteria of genre
Staphylococcus, Streptococcus, Enterococcus. These
outer membrane and several layers of peptidoglycan.
bacteria are the most common cause of clinical
The outer membrane is composed of lipoproteins,
phospholipids, and LPS. The peptidoglycan stays intact infections.
to lipoproteins of the outer membrane that is located in
the fluid-like periplasm between the plasma membrane Which is more harmful- gram-positive bacteria or
gram-negative bacteria?
and the outer membrane. The periplasm is contained
with proteins and degrading enzymes which assist in
Gram-negative bacteria are more harmful and cause
transporting molecules.
certain diseases. Their outer membranes are hidden by a
The cell walls of the gram-negative bacteria, unlike the slime layer that hides the antigens present in the cell.
gram-positive, lacks the teichoic acid. Due to the
presence of porins, the outer membrane is permeable to Is it easier to kill gram-positive bacteria?
nutrition, water, food, iron, etc.
The cell wall of the gram-positive bacteria absorbs
antibiotics and cleaning products. Because of the outer
Gram Staining
peptidoglycan layer, they are easier to kill. Gramnegative bacteria cannot be killed easily.
What infections are caused by gram-positive bacteria?
Gram-positive bacteria usually cause Urinary Tract
Infections. These are caused commonly in people who
are more prone to urinary tract infections or are elderly
or pregnant.
Which infections are caused by gram-negative
bacteria?
The gram-negative bacteria cause various infections in
humans such as indigestion, food poisoning,
pneumonia, meningitis and other bacterial infections in
the blood cells, bloodstream, wound infections, etc. The
infections are caused by Acinetobacter, Pseudomonas
aeruginosa and E.coli.