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  1. Organisms are composed of cells. Some of them are composed of a single cell which are called unicellular organisms while others, like us, composed of many cells, and  are called multicellular organisms.
  2. So organisms with a single cell are Unicellular organisms. Unicellular organisms grow by cell division.
  3. In unicellular organisms, all functions like digestion, respiration and reproduction are performed by a single cell.
  4. Bacteria are unicellular organisms and they are prokaryotic. They do not have a membrane bound nucleus and membrane bound organelles.
  5. Unicellular organisms like bacteria, unicellular algae or Amoeba, reproduction is synonymous with growth, i.e., increase in number of cells.
  6. The archaea are a group of unicellular organisms as they survive under extremely harsh environmental conditions
  7. Most protists are unicellular organisms.
  8. Unicellular organisms reproduce asexually by cell division or binary fission of the parent cell.
  9. In unicellular organisms, the primary change that occurs following cell division is cell enlargement.

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