The four nutritional categories found in bacteria are:

  1. Autotrophs: synthesize their own organic food.
  2. Saprotrophs: feed on dead organic matter.
  3. Symbionts: use food from other living organisms with which they are associated for mutual benefit.
  4. Parasites: absorb food from living organisms and cause harm to them.


Respiration in bacteria may be either aerobic (using oxygen for respiration) or anaerobic (respiration in the absence of oxygen).

Cellular respiration or breakdown of food to release energy occurs in mesosomes which are the inner extensions of the cell membrane.


Asexual Reproduction

Bacteria reproduce asexually by binary fission. Under favourable conditions, it takes about 20 minutes for one bacterium cell to divide into two by binary fission.

Sexual Recombination (Genetic Recombination)

Some bacteria show a primitive mode of sexual reproduction. It is different from sexual reproduction in higher forms. The steps are:

  • (a) Two conjugating (lie very close for transfer of genes) bacteria are held together by pili.
  • (b) A segment of DNA strand is transferred from one bacterium to another bacterium. F-factor (sex-factor) is transferred from male donor cell to female (recipient) cell.