Roles of structures found in bacteria cells

The cell wall - A physical barrier that protects against mechanical damage and excludes certain substances

The capsule - Protects bacterium from other cells and helps groups of bacteria to stick together for further protection

Cell surface membrane - Acts as a differentially permeable layer which controls the entry and exit of chemicals

Flagellum - Aids movement of bacterium because its rigid, corkscrew shape and rotating base help the cell spin through fluids

Circular DNA - Possesses the genetic information for the replication of bacterial cells

Plasmid - Possesses genes that aid the survival of bacteria in adverse conditions, e.g. produces enzymes which break down anti bodies.

Flagellum - There may be more than one and is used for locomotion (only certain species)

Nuclear material - Comprises a large circle of DNA

Cytoplasm - jelly like contains enzymes and other soluble materials

Ribosomes - Smaller than in eukaryotic cells

Capsule - A mucilaginous layer of slime (Only certain species)

Cell wall - Made of polypeptides and polysaccharides

Cell surface membrane

Plasmid - Small circular piece of DNA (Only certain species)

Vibrio cholerae is transmitted by ingestion of water or more rarely food thats been contaminated with faecal material containing this pathogen. Once ingested:

Almost all vibrio cholerae bacteria ingested by humans are killed by the acidic conditions in stomach. Some survive especially of P.H is above 4.5

When surviving bacteria reach small intestine they use their glagella to propel themselves in corkscrew like fashion through mucus lining of intestinal wall.

They then start producing toxic protein which has 2 parts. The first binds to specific carbohydrate receptors on cell surface membrane. As only epithelial cells of small intestine have these specific receptors, it explains why cholera toxin only affects this region of the body.

Other toxic part enters epithelial cells which causes ion channels of cell surface membrane to open, so chloride ions that are normally contained within the epithelial cells flood into the lumen of the intestine.

Loss of chloride ions from epithelial cells raises their water potential while the increase of chloride ions in the lumen of the intestine lowers its water potential.

Water flows from cells into the lumen.

Loss of ions from epithelial cells establishes concentration gradient. Ions therefore move by diffusion into epithelial cells from surrounding tissues including the blood. This establishes a water potential gradient that causes water to move by osmosis from blood and other tissues into the intestine.

Its this loss of water from the blood and other tissues, into the intestine, that causes the symptoms of cholera.

Just drinking water is ineffective because water isnt being abosrbed from intestine. In the case of cholera, water is being lost from cells.Drinking of water does not replace the electrolytes (ions) that are being lost from the epithelial cells of the intestine.

Rehydration solution needs to contain:

Water - To rehydrate the tissues

Sodium - Replace sodium ions lost from epithelium of the intestine and to make optimum use of the alternative sodium glucose carrier protein.

Glucose - Stimulate the uptake of sodium ions from intestine and provide energy

Potassium - Replace lost potassium ions and stimulate appetite

Electrolyes - Such as chloride and citrate ions, help prevent electrolyte imbalance.