5. Bacteria containing a tuft of flagella that comes out from one pole is called ___.

(A) Lophotrichous

(B) Peritrichous

(D) Amphitrichous

Lophotrichous Bacteria Explained: Tuft of Flagella at One Pole

Introduction

Flagella are specialized locomotory organelles that enable many bacteria to move actively through liquid or semi-solid environments. This movement allows bacteria to locate nutrients, escape harmful substances, colonize new habitats, and establish infections in host organisms. Bacterial motility is therefore an essential factor contributing to survival, adaptation, and pathogenicity. The number and arrangement of flagella on the bacterial surface vary among different species and form an important basis for bacterial identification and classification.

Based on the distribution of flagella, bacteria are classified into several categories such as monotrichous, lophotrichous, amphitrichous, and peritrichous. Each arrangement provides distinct patterns of movement and reflects evolutionary adaptations to different ecological niches.

Correct Answer

Correct Option: (A) Lophotrichous

Detailed Explanation

The term lophotrichous is derived from the Greek word lopho, meaning “tuft.” A lophotrichous bacterium possesses a cluster or tuft of multiple flagella emerging from one pole of the bacterial cell. These flagella rotate together in a coordinated manner, enabling rapid swimming and efficient directional movement in liquid environments.

The arrangement of bacterial flagella is determined genetically and represents an important taxonomic characteristic. Lophotrichous bacteria are capable of moving efficiently toward favorable environmental conditions by a process known as chemotaxis. The coordinated rotation of multiple polar flagella provides greater propulsion than a single flagellum, allowing these bacteria to respond quickly to nutrient gradients or escape harmful chemicals.

It is important to distinguish lophotrichous bacteria from other flagellar arrangements. Monotrichous bacteria possess only a single flagellum at one pole, amphitrichous bacteria possess one flagellum or a tuft at both poles, and peritrichous bacteria possess numerous flagella distributed over the entire cell surface. Since the question specifically describes a tuft of flagella at one pole, the correct answer is lophotrichous.

Explanation of Each Option

Option (A): Lophotrichous

This option is correct. Lophotrichous bacteria possess a tuft of flagella arising from one pole of the cell. The coordinated movement of these flagella enables rapid and directed swimming.

Option (B): Peritrichous

This option is incorrect. Peritrichous bacteria possess numerous flagella distributed over the entire surface of the bacterial cell rather than at one pole.

Option (C): Monotrichous

This option is incorrect. Monotrichous bacteria possess only one flagellum at a single pole rather than a tuft of flagella.

Option (D): Amphitrichous

This option is incorrect. Amphitrichous bacteria possess flagella at both poles, either as single flagella or tufts.

Why Option (A) is Correct

The defining feature of lophotrichous bacteria is the presence of multiple flagella emerging together from one pole. This exactly matches the description given in the question.

Why the Other Options are Incorrect

Why Option (B) is Incorrect

Peritrichous bacteria have flagella surrounding the entire bacterial surface rather than forming a polar tuft.

Why Option (C) is Incorrect

Monotrichous bacteria possess only a single polar flagellum and therefore do not have a tuft.

Why Option (D) is Incorrect

Amphitrichous bacteria possess flagella at both ends of the bacterial cell, not exclusively at one pole.

Comparison of All Options

Option	Flagellar Arrangement	Correct or Incorrect
A	Tuft of flagella at one pole	Correct
B	Flagella distributed all over the cell	Incorrect
C	Single flagellum at one pole	Incorrect
D	Flagella at both poles	Incorrect

Types of Bacterial Flagellar Arrangement

Arrangement	Description	Example
Atrichous	No flagella	Klebsiella species
Monotrichous	Single flagellum at one pole	Vibrio cholerae
Lophotrichous	Tuft of flagella at one pole	Helicobacter pylori
Amphitrichous	One flagellum or tuft at both poles	Spirillum volutans
Peritrichous	Flagella distributed over the entire surface	Escherichia coli, Salmonella

Functions of Bacterial Flagella

Function	Importance
Motility	Enables bacterial movement
Chemotaxis	Movement toward nutrients and away from toxins
Colonization	Helps bacteria establish infection
Biofilm Formation	Facilitates surface attachment during early stages
Environmental Adaptation	Improves survival in changing environments

Structure of a Bacterial Flagellum

Component	Function
Filament	Long external structure composed of flagellin
Hook	Connects filament to basal body
Basal Body	Anchors the flagellum and functions as the rotary motor

Comparison of Important Bacterial Surface Structures

Structure	Main Component	Primary Function
Flagella	Flagellin	Motility
Pili	Pilin	Attachment and conjugation
Capsule	Polysaccharides	Protection against phagocytosis
Endospore	Calcium dipicolinate	Survival under adverse conditions

Biological Significance

Flagellar arrangement reflects the evolutionary adaptation of bacteria to different ecological environments. Lophotrichous bacteria benefit from multiple coordinated flagella that provide stronger propulsion and improved chemotactic responses. Efficient motility allows bacteria to locate nutrients, colonize host tissues, escape unfavorable conditions, and enhance their survival. Consequently, flagella are not only locomotory organelles but also important virulence factors in many pathogenic bacteria.

Final Answer