Morphology of Bacteria: Size, Shape and Arrangement (2023)

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  • Last Modified 19-07-2022

Morphology of Bacteria: Size, Shape and Arrangement (1)

Morphology of Bacteria: What is pleomorphism? What are the types of bacteria? Do all bacteria have similar shapes and sizes? Bacteria are microorganisms that belong to the phylum Monera. Morphology of Bacteria deals with the bacterial outer structure, shape and sizes. To know more about the Morphology of Bacteria, scroll down the article.

Know what is Bacteria in detail here

What are Bacteria?

Bacteria are prokaryotic microorganisms and are unicellular in nature.Since they lack a membrane-bound nucleus, they are less complex than other living creatures. Although only some bacteria can be seen by our naked eyes while the rest are microscopic in nature, they display a wide range of shapes, sizes, and structures.

Morphology of Bacteria: Size, Shape and Arrangement (2)

Fig: Bacteria

What are the Characteristics of Bacteria?

Some of the basic characteristics of bacteria are as follows:

I. Bacteria are microorganisms with only one cell and without a nucleus or membrane-bound organelles.
II. A plasmid is an additional circular of genetic material found in some bacteria.
III. They do not possess internal organisation and their DNA is often sequestered into a region of the bacterial cell known as the nucleoid.
IV. Bacteria have a cell wall that is often made of peptidoglycan, which is a complex molecule consisting of sugars and amino acids.
V. Bacteria may be found in all types of environments on Earth, including soil, rock, seas, and even polar snow.
VI. The binary fission method is used by bacteria to reproduce. The bacteria, which is a single cell, splits into two identical daughter cells throughout this procedure.
VII. These bacteria can be pathogenic or non-pathogenic in nature.

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What is the Morphology of Bacteria?

i. A bacteria’s greatest distinguishing characteristic is its morphology or shape. It’s a certain species’ distinguishing feature.
ii. The shape of a bacterium cell is determined by its morphology, which also determines the pathogenicity of the bacteria.
iii. The adaptation and evolution of bacteria are influenced by their morphological characteristics.
iv. The peptidoglycan (murein) in the bacterial cell wall and is a polymer of sugars that alternates \({\text{N}}\)-acetylglucosamine (NAG) connected to \({\text{N}}\)-acetylmuramic acid (NAM) and amino acids in a peptide chain.
v. The varying morphology and form of bacteria are due to changes in the polymer’s structure and thickness.

Different Sizes of Bacteria

i. Bacteria are about a tenth of the size of eukaryotic cells. Bacteria range in size from \(0.5\) to \(5\mu {\text{m}}\) on average.
ii. They can, however, be as little as \(0.3\,{\text{m}}\) and as big as \(0.7\,{\text{mm}}{\text{.}}\)
iii. The unaided eye’s resolution limit is around \(200\) microns, and because many bacteria are smaller than this, they are invisible to the human eye.
iv. Thiomargarita namibiensis, which may grow to be half a millimetre long, and Epulopiscium fishelsoni, which can grow to be \(0.75\) millimetres long, are among the biggest bacteria.
v. Members of the genus Mycoplasma are the smallest bacteria, measuring about \(0.3\,\mu {\text{m}}\) and being as small as the smallest viruses.
vi. The diameter of common bacteria such as Escherichia coli ranges from \(1.1\) to \(1.5\,\mu {\text{m}}{\text{.}}\)

Different Shapes of Bacteria

i. The majority of bacteria have a rigid cell wall that gives them a defined form while also protecting their internal components.
ii. Even while the majority of bacteria have this characteristic, they vary in shape, allowing them to be categorised into distinct categories depending on their morphologies.
iii. The bacterial cell wall and cytoskeleton are responsible for a broad range of forms.
iv. The common categories of bacteria based on their shapes are as follows:

A. Cocci

a. The bacteria that are oval or spherical in shape are known as cocci bacteria.
b. These can be solitary or connected to one another in a group. When grouped together, they seem flattened.
c. Coccoid forms are thought to have evolved from rod-shaped creatures throughout evolutionary time.

Arrangements of Cocci

a. Cocci bacteria can be organised individually, in pairs, in four-cell groups, in chains, in clusters, or in eight-cell cubes.
b. During cell division, these cells stay together. The bacteria’s form is altered by the plane of cell division.
c. Cocci have a gram-positive cell wall with a thick peptidoglycan layer or a gram-negative cell wall with a thin peptidoglycan layer.
d. According to the arrangement of cells, the cocci are again divided into the following subtypes:

1. Monococcus – It is a bacterial species that consists of a single cell.

2. Diplococcus
i. When two bacterial cells form a pair, this configuration occurs (joined together).
ii. Some cells in this arrangement may be spherical, while others may be flattened, elongated, or bean-shaped.
iii. Examples: Streptococcus pneumoniae.

3. Streptococcus
i. In this type, the bacteria are organised in long chains here.
ii. These bacteria belong to the Streptococcaceae family, which is characterised by Gram-positive bacteria and a lack of motility.
iii. Streptococcus pneumonia, Streptococcus pyogenes, and Streptococcus mutans are some examples.

4. Tetrads
i. Tetrad bacteria are organised in a group of four cells that remain connected during cell division and development in the attachment.
ii. When the cells split into two planes, this pattern occurs.
iii. Aerococcus, Pediococcus, and Tetragenococcus are some examples.

5. Staphylococcus
i. Bacteria organised in grape-like clusters make up this kind of arrangement.
ii. This is caused by cell division in both planes and is characterised by immotile and Gram-positive organisms.
iii. Staphylococcus haemolyticus, Staphylococcus capitis, Staphylococcus aureus, and other bacteria are examples.

6. Sarcinae
i. The bacterial cells form an eight-cell cluster in this configuration.
ii. This happens when the cells divide in a perpendicular plane.
iii. The fact that these organisms are strictly anaerobic in nature.
iv. Sarcina lutea, Sarcina aurantiaca, and Sarcina ventriculi are other examples.

Morphology of Bacteria: Size, Shape and Arrangement (3)

Fig: Arrangements of Cocci

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B.Bacilli (Rod-shaped)

These are rod-shaped cells that, like cocci, can exist alone or in association with other cells. Bacilli bacteria were among the earliest to emerge, and their form is considered to be less favourable than that of other bacteria.

Arrangement of Bacilli

1. Bacillus
i. Bacilli are bacteria that are rod-shaped and exist as solitary cells.
ii. These bacteria are facultative anaerobes that may generate endospores
iii.Salmonella enterica subsp., Bacillus cereus and Salmonella choleraesuis are some examples.

2. Diplobacilli
i. Diplobacilli, like Diplococci, is found in pairs.
ii. The two cells do not divide and develop in an associated configuration after cell division.
iii. Coxiella burnetii, Klebsiella rhinoscleromatis, and Moraxella bovis are some examples.

3. Streptobacilli
i. Bacteria in this category are arranged in chains.
ii. This happens when a single chain of cells divides.
iii. Streptobacillus moniliformis, Streptobacillus felis, Streptobacillus Levaditi, and Streptobacillus hongkongensis are examples of streptobacilli.

4. Coccobacilli
i. As the name indicates, Coccobacilli is similar to both cocci and bacilli.
ii. Because they are smaller, they look stumpy.
iii. Chlamydia trachomatis, Gardnerella vaginalis, and Haemophilus influenzae are some of the examples.

5. Palisades
i. Palisades are bacilli bacteria that have a picket fence-like shape due to a bend at the site of division during cell division.
ii. They have the appearance of Chinese characters.
iii. Example – Corynebacterium diphtheria.

Morphology of Bacteria: Size, Shape and Arrangement (4)

Fig: Arrangements of Bacilli


This group of microorganisms includes bacteria that are either helical-shaped or curved or comma-shaped. The bacterium might have a corkscrew-like spiral or be slightly bent.

1. Vibrio
i. These are the comma-shaped bacteria that are slightly bent.
ii. Vibrio mytili, Vibrio anguillarum, Vibrio parahaemolyticus, and Vibrio cholera are some examples.

Morphology of Bacteria: Size, Shape and Arrangement (5)

Fig: Vibrio

2. Spirochetes
i. Spirochetes are spiral bacteria that have a helical shape.
ii. These organisms are flexible and have an axial filament which helps in motility. These filaments are a key feature that distinguishes spirochetes from other bacteria.
iii. These filaments travel the length of the bacterium, aiding in the twisting of the bacteria’s motility.
iv. Examples include Leptospira interrogans, Treponema pallidum, etc.

Morphology of Bacteria: Size, Shape and Arrangement (6)

Fig: Spirochetes

3. Spirilla (Helical-shaped/Corkscrew form)
i. Spirochetes have a similar structure to these bacteria, although they are more rigid.
ii. They, too, have a flagellum, but unlike spirochetes, they lack the endoflagella.
iii. Helicobacter pylori, Campylobacter jejuni, and Spirillum winogradskyi are some of the examples.

Morphology of Bacteria: Size, Shape and Arrangement (7)

Fig: Spirillum

Other Shapes and Arrangements

Some of the other shapes and arrangements are as follows:
1. Filamentous Bacteria
i. These are filament-shaped bacteria that are thin, long, and are filamentous.
ii. They can split into mycelium-like branches that look like strands of hair or spaghetti.
iii. Actinomycetes are a good example.

2. Appendaged Bacteria
i. Appendaged bacteria are bacteria that generate a distinct structure, such as pillus or fimbriae.
ii. These bacteria are more virulent when compared to the other bacteria that do not form these appendages.
iii. Example – Neisseria gonorrhoea.

3. Club-shaped Rod Bacteria
i. One side of these bacteria is thinner than the other.
ii. Corynebacterium is a well-known representative of this group.

4. Box-shaped/ Rectangular Bacteria
i. Bacteria with a box-like form or that are rectangular in shape.
ii. Box-shaped bacteria have a rectangular form that resembles the shape of a box.
iii. Example – Haloarcula marismortui.

5. Triangular-shaped Bacteria
i. This group includes bacteria that are triangular in shape.
ii. Example: Haloarcula.

6. Pleomorphic Bacteria
i. The bacteria that belong to this group does not have or possess a specific shape.
ii. They can alter the shape, although they appear to have a distinct morphology in pure cultivation.
iii. Examples: Mycoplasma.

7. Star-shaped Bacteria
i. The bacteria that look like stars or are star-shaped are included in this group of bacteria.
ii. Examples: Stella humosa.

8. Stalked Bacteria
i. These are the bacteria that possess a stalk on one end of the cell.
ii. Examples: Caulobacter crescentus.


Bacteria are unicellular organisms that are prokaryotic in nature. Through this article, we understood that bacteria comes in various sizes and shapes. There are many pathogenic bacteria that are responsible for different diseases in living organisms. There are some bacteria that do not have any shape and are considered pleomorphic like organisms.

The form of a bacterium cell is determined by its morphology, which also determines its virulence. The peptidoglycan (murein) in the bacterial cell wall is a polymer of sugars that alternates \({\text{N}}\)-acetylglucosamine (NAG) connected to \({\text{N}}\)-acetylmuramic acid (NAM) and amino acids in a peptide chain.

Attempt Mock Tests


Q.1. What are the three different types of bacterial morphology?
Ans: The three different types of bacterial morphology are cocci, bacillus and spiral.

Q.2. What are the two main classifications of bacteria?
Ans: The two main classifications of bacteria are gram positive-bacteria and gram-negative bacteria.

Q.3. What do you mean by morphology?
Ans: Morphology is the study of the shape and structure of organisms.

Q.4. What are the main characteristics of bacteria?
Ans: Some of the main characteristics of a bacteria are as follows:
i. Organelles that are membrane-bound are absent in bacteria.
ii. These are single-celled microorganisms that are typically small in size and are visible under a microscope.
iii. They have a cell wall, i.e., composed of peptidoglycanand may be distinguished using the gram staining technique.

Q.5.What is the most common type of bacteria?
Ans: The most common type of bacteria is Escherichia coli.

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We hope this detailed article on the Morphology of Bacteria helps you in your preparation. If you get stuck do let us know in the comments section below and we will get back to you at the earliest.


Morphology of Bacteria: Size, Shape and Arrangement? ›

There are three basic shapes of bacteria: coccus

A coccus (plural cocci) is any bacterium or archaeon that has a spherical, ovoid, or generally round shape. Bacteria are categorized based on their shapes into three classes: cocci (spherical-shaped), bacillus (rod-shaped) and spiral (of which there are two types: spirillum and spirochete). › wiki › Coccus
, bacillus
A bacillus ( PL bacilli), also called a bacilliform bacterium or often just a rod (when the context makes the sense clear), is a rod-shaped bacterium or archaeon. Bacilli are found in many different taxonomic groups of bacteria. › wiki › Bacillus_(shape)
, and spiral
. Based on planes of division, the coccus shape can appear in several distinct arrangements: diplococcus, streptococcus, tetrad, sarcina, and staphylococcus. The bacillus shape can appear as a single bacillus, a streptobacillus, or a coccobacillus.

What is the morphology shape and arrangement of bacteria? ›

Bacteria have characteristic shapes (cocci, rods, spirals, etc.) and often occur in characteristic aggregates (pairs, chains, tetrads, clusters, etc.). These traits are usually typical for a genus and are diagnostically useful.

What is the size of bacteria morphology? ›

Bacteria cell is 10 times smaller than the human cell. The diameter of a bacteria cell is ~1µm (10-6 m) The outer covering of a bacteria cell is the cell wall, which is rigid and provides structural integrity.

What are the 3 basic morphological shapes of bacterial cells? ›

The three basic shapes of bacteria are bacillus (rod-shaped), coccus (spherical-shaped), and spirillum (spiral-shaped). This simple model allows students to build the three shapes of bacteria in a short period of time.

What determines the arrangement of bacterial cells? ›

The apparent shape of a bacterium is determined by the geometry of its growing cell wall (1–4). Recently, a number of prokaryotic cytoskeletal proteins, such as FtsZ, MreB, and crescentin, have been shown to be important for shaping the bacterial cell (4–7).

What is the morphology of bacteria? ›

The term morphology comes from the Greek for form and means the form and structure of living organisms. The morphology of bacteria describes the external appearance of bacterial cells including shape, arrangement, and size.

What is the morphology of a bacteria? ›

The morphology and arrangement of bacteria are often a key factor in identifying their species. Their direct examination under the light microscope enables the classification of these Bacteria and Archaea . Generally, the basic morphologies are spheres (coccus) and round-ended cylinders or rod shaped (bacillus).

What is the size of a bacterial cell? ›

An average-size bacterium—such as the rod-shaped Escherichia coli, a normal inhabitant of the intestinal tract of humans and animals—is about 2 micrometres (μm; millionths of a metre) long and 0.5 μm in diameter, and the spherical cells of Staphylococcus aureus are up to 1 μm in diameter.

What are the different types of arrangement of bacteria? ›

In fact, structure of bacteria has two aspects, arrangement and shape. So far as the arrangement is concerned, it may Paired (diplo), Grape-like clusters (staphylo) or Chains (strepto). In shape they may principally be Rods (bacilli), Spheres (cocci), and Spirals (spirillum).

What is the size range of bacteria? ›

Most bacteria are 0.2μm (micron) in diameter and 2−8μm (micron) in length. Bacterial cells are about one-tenth the size of eukaryotic cells.

What are the three arrangements of bacteria? ›

There are three basic shapes of bacteria: coccus, bacillus, and spiral. Based on planes of division, the coccus shape can appear in several distinct arrangements: diplococcus, streptococcus, tetrad, sarcina, and staphylococcus. The bacillus shape can appear as a single bacillus, a streptobacillus, or a coccobacillus.

What influences bacterial shape and arrangement? ›

Specifically, cell shape is driven by eight general considerations: nutrient access, cell division and segregation, attachment to surfaces, passive dispersal, active motility, polar differentiation, the need to escape predators, and the advantages of cellular differentiation.

Why do bacteria have different arrangements? ›

Simply put, bacteria with different shapes present different physical features to the outside world, and these features help cells cope with and adapt to external conditions.

How are bacteria classified by size? ›

Bacteria are microscopic with a wide range of sizes from 0.2 μm to 100 μm. Cocci are generally of 0.2 to 1.0 μm. Bacilli are generally of 1.0 μm 5 μm in length and 0.5 to 1.0 μm in diameter. Spirochetes are generally 20 μm in length and 0.1 to 1.0 μm in diameter.

What are the sizes in colony morphology? ›

Morphology of Bacterial Colony
  • Surface Appearance – Can be smooth, rough/granular, dull, shiny or wrinkled.
  • Size – A representative bacterial colony's diameter can be measured in millimetres and can be categorised as large (>1 mm), medium (=1 mm), small (<1 mm) and pinpoint (<0.5 mm).

What are the 5 types of morphology of bacteria? ›

Morphology of Bacteria- Sizes, Shapes, Arrangements, Examples
  • Bacterial Size.
  • Bacterial Shape. Cocci. Bacilli (Rod-shaped) Spiral.
  • Arrangements of Cocci. Coccus. Diplococci. Tetrad. ...
  • Arrangement of Bacilli. Bacillus. Diplobacilli. ...
  • Arrangement of Spiral. Vibrio. Spirochetes. ...
  • Other Shapes and Arrangements.
  • References.
  • Sources.
May 3, 2023

What is the shape of a bacterial cell? ›

Bacteria have distinct cell body shapes, ranging from spheres (cocci) to rods (bacilli) of various curvatures and helicities and to more exotic shapes, such as stars, formed by elaboration of prosthecae through polar growth.

How do you describe cell morphology? ›

Cell morphology describes the shape, structure, form, and size of cells.

What are the 5 characteristics of bacteria? ›

Five characteristics of bacteria include being unicellular, prokaryotic, microscopic, lacking a nucleus, and having a plasma membrane.

What is the size and shape of a cell? ›

Considering an animal cell, we can generalize the shape of a cell as round (spherical) or irregular. Plant cells are much more rigid and rectangular in shape. The size of a cell can be as small as 0.0001 mm (mycoplasma) and as large as six to twelve inches (Caulerpa taxifolia).

What is bacterial arrangement? ›

Morphology. Microbiologists can also identify bacteria through their colony morphology, or the appearance and characteristics of the bacterial colony. While arrangement refers to the groupings of individual cells, morphology describes the appearance of groups of bacteria, or colonies.

What is arrangement of bacteria in chain called? ›

Pairs of cocci are called diplococci; rows or chains of such cells are called streptococci; grapelike clusters of cells, staphylococci; packets of eight or more cells, sarcinae; and groups of four cells in a square arrangement, tetrads.

What is morphology in microbiology? ›

morphology, in biology, the study of the size, shape, and structure of animals, plants, and microorganisms and of the relationships of their constituent parts. The term refers to the general aspects of biological form and arrangement of the parts of a plant or an animal.

What are the different types of cell arrangement? ›

The basic types of arrangement are single (one), diplo (pair), tetrad (four, square), sarcina (eight, cube), staphylo arrangement (cluster), and strepto- arrangement (sheets, chains). So, Staphylococcu would appear as a cluster of round cells, like grapes, when viewed under a microscope.

What are 3 characteristics of the structure of most bacteria? ›

There are three notable common traits of bacteria, 1) lack of membrane-bound organelles, 2) unicellular and 3) small (usually microscopic) size.

What is the smallest form of bacteria called? ›

Smallest Bacteria : Mycoplasma gallisepticum. Mycoplasma gallisepticum is a parasite bacteria with the size from 0.2 to 0.3 micrometer is known to be smallest bacteria.

What is the shape and arrangement of the E coli cell? ›

The bacterium Escherichia coli is rod-shaped, and a unit cell keeps regular dimensions of about 1.5 µm long and 0.5 µm wide. The rod-shaped cell is composed of two parts: a cylinder in the center and caps at both ends. The length of the cylinder corresponds to the length of the rod cell.

What are the 4 types of bacteria shapes? ›

Bacteria are classified into five groups according to their basic shapes: spherical (cocci), rod (bacilli), spiral (spirilla), comma (vibrios) or corkscrew (spirochaetes).

What factors affecting shape and size of bacterial colonies? ›

Two of the main factors that affect bacterial growth in a laboratory are media nutrient density and media hardness, the latter being a result of agar concentration. Bacteria form distinct morphotypes based on these factors, and there are usually sharp transitions between morphotypes [2].

What are the characteristics of shapes of bacteria? ›

Individual bacteria can assume one of three basic shapes: spherical (coccus), rodlike (bacillus), or curved (vibrio, spirillum, or spirochete). Considerable variation is seen in the actual shapes of bacteria, and cells can be stretched or compressed in one dimension.

What is shape and arrangement of staphylococci? ›

Structure. Staphylococci are Gram-positive cocci about 0.5 – 1.0 μm in diameter. They grow in clusters, pairs and occasionally in short chains. The clusters arise because staphylococci divide in two planes.

What shape and arrangement is spiral bacteria? ›

Spirilla (sing. spirillum) shapes are curved-shaped bacteria which can range from a gently curved shape to a corkscrew spiral. Many spirilla are rigid and able to move. The length of rod-shaped bacteria is over 2–100 μm.

What are the factors influencing bacteria shape and arrangement? ›

Specifically, cell shape is driven by eight general considerations: nutrient access, cell division and segregation, attachment to surfaces, passive dispersal, active motility, polar differentiation, the need to escape predators, and the advantages of cellular differentiation.

What are the types of bacteria based on arrangements? ›

Classification of Bacteria:
  • On the basis of arrangement and the number of flagella, the bacteria can be classified into four groups.
  • These are monotrichous , amphitrichous, lophotrichous, and peritrichous.

What is the size shape and arrangement of E coli? ›

The bacterium Escherichia coli is rod-shaped, and a unit cell keeps regular dimensions of about 1.5 µm long and 0.5 µm wide. The rod-shaped cell is composed of two parts: a cylinder in the center and caps at both ends.

What is the arrangement of bacilli? ›

Bacilli usually divide in the same plane and are solitary, but can combine to form diplobacilli, streptobacilli, and palisades. Diplobacilli: Two bacilli arranged side by side with each other. Streptobacilli: Bacilli arranged in chains. Coccobacillus: Oval and similar to coccus (circular shaped bacterium).

What is an example of a square shaped bacteria? ›

Haloquadratum (common abbreviation: Hqr.) is a genus of archaean, belonging to the family Haloferacaceae. The first species to be identified in this group, Haloquadratum walsbyi, is unusual in that its cells are shaped like square, flat boxes.


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