Bacteria REVIEW

Bacteria Bacteria are single-celled organisms Are present in air, water and on most solid materials Bacterial cells are very small and can only be seen with the aid of a microscope.

Bacterial Shapes When observed under a microscope the cells can be seen to differ in shape and in conformation of groups of cells. Cells are either spherical or rod-shaped Spherical bacteria are called cocci Those that are rod shaped are called bacilli. This is the first basis for differentiating between bacterial cells.

Rod-shaped & Spherical Bacteria Bacteria are also classified according to cell cluster formation: Diplococci        * two cocci cells paired Staphylococci  * a number of cells clustered together Streptococci    * a number of cells arranged in a chain

Bacterial characteristics Some bacteria are capable of locomotion by means of flagellae long, hair-like appendages growing out of the cell Some rod-shaped bacteria contain spores These are formed when the cells are faced with adverse conditions, such as high temperature once suitable conditions are reestablished the spores germinate to form new cells.

Bacterial Components Close examination of the simple cell reveals that it is composed of the following components : Cell wall-this gives the cell its shape and retains the constituents Cell membrane-used for filtering in food constituents and discharging waste products Nucleoid-where the genetic material of the cell is stored; Cytoplasm- a semiliquid proteinaceous substance which contains starch, fat and enzymes.

The cell membrane is semipermeable and allows the cell to feed by osmosis i.e. the exchange of water between the cytoplasm of a living cell and the surrounding watery material. Only small molecules can pass in and out of the cell e.g. with a sugar solution on one side of a semipermeable membrane and water on the other, water will diffuse in, diluting the sugar solution. The sugar molecules cannot pass out so a hydrostatic pressure, known as osmotic pressure, develops. Bacteria can feed by selective intake of nutrients dissolved in water. They can also take in nutrients against the normal osmotic flow active transport.