The flagella is composed of the filament, hook and basal body. The hook and filament are composed of protein subunits called flagellin, which is synthesized within the cell. The filament extends outside the cell wall and is connected to the hook at the surface of the cell. The hook and basal body are embedded in the cellular envelope. 

Structure of the Flagella

There are two types of bacterial movements that are facilitated by flagella: 
- Running
- Tumbling

Directional Movement of Bacteria

There are many environmental signals bacteria sense that influence their movement in the form of a taxis. These taxes are: 
- Phototaxis
- Magnetotaxis
- Chemotaxis

Taxis Influencing Bacterial Movement 

The arrangement of the flagella is organized into four types:
- Monotrichous 
- Lophotrichous
- Amphitrichous 
- Peritrichous 

Arrangement of Flagella

Flagella are hair like filaments that extend from the cytoplasmic membrane to the external part of the cell. The flagella functions in cell motility. 

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- Cell Wall
- Plasma Membrane
- Cytoplasm
- Ribosomes
- Mesosomes
- Cytoplasmic Inclusions
- Nucleoid
- Capsule
- Flagella
- Pilus
- Fimbriae
- Plasmid DNA
- Endospore
- Inclusion Bodies

Bacterial Structures

Al-mohanna, Moshtaq & H., quine. (2016). MORPHOLOGY AND CLASSIFICATION OF BACTERIA. 

Morphology and Classification of Bacteria

The cell wall in bacterial cells is very rigid and provides a stable shape to the cell. It is essential for bacterial growth and division. It is important in preventing the cell from bursting from osmotic pressure changes.

Cell Wall

The cytoplasm consists of organic and inorganic solutes and free floating ribosomes. Chromosomal DNA and plasmids are located in this region.

Cytoplasm

Mesosomes store respiratory enzymes and aid in cellular reproduction. These vesicles are formed by the invagination of the plasma membrane into the cytoplasm. 

Mesosomes

Inclusions can store nutrients or gas needed for the cells metabolism or buoyancy. Inclusions are important in reducing build up of osmotic pressure as the cell accumulates compounds.

Cytoplasmic Inclusions

The capsule is the extracellular layer of the bacterial cell. Generally, they are composed of polysaccharides and proteins. The capsule may allow a bacteria to be more infectious by making it more difficult to be engulfed by white blood cells. 

Capsule

Flagella

This structure is found in both gram positive and gram negative bacteria. It is located under the cell wall and acts as a semipermeable barrier, controlling the flow of metabolites, between the cell wall and the cytoplasm. 

Plasma Membrane

Fimbriae are short bristle-like strands that extend from the bacteria by the hundreds. They are important in cell adhesion, infection, and colonization.

Fimbriae

The pilus is a appendage that extends to reach surfaces or other bacteria. The sex pilus is a specific pilus important in transferring DNA between bacterial cells.

Pilus

Prokaryotes do not have a nucleus. DNA and DNA-associated proteins are in the nucleoid region. It is a condensed area of DNA in the cell.

Nucleoid

Plasmids are circular, extrachromosomal DNA. Cells can have hundreds of plasmids. They can carry important genes for antibiotic resistance or conjugation.

Plasmid DNA 

Ribosomes are made up of RNA and proteins. They are responsible for translating mRNA into proteins. Ribosomes are present in the cytoplasm.

Ribosomes

Some bacteria are capable of forming endospores through the process of sporulation. The endospore contains that bacterial genome and keeps the bacterium in a dormant state. It is formed when the vegetative cell forms a septum and divides asymmetrically. This action separates the DNA forespore from the cell to eventually form the endospore. The bacterial forms the endospore when in environment is not suitable for growth. It also allows the bacterium to be dormant when exposed to harsh chemicals, radiation or low nutrients.

Endospores

Some bacteria are capable of forming inclusion bodies which are used for holding excess materials like nutrients or proteins. These cell structures decrease osmotic pressure in the cell by containing these compounds in inclusion bodies. 

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