Paramecium Cells

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Paramecium cells are large unicellular organisms. They are part of the eukaryotic family, thus meaning that they have membrane-bound organelles.

Paramecium is free living ciliated Protozoa, its cell body is surrounded by cilia.  THere are two main functions of these cilia.  Firstly they allow paramecium to move around its freshwater habitat.  Secondly, they are also used to waft small bacteria and algaes into the gullet (a large invagination in the cell membrane) where they are endocytosed and assymilated into the cell. All waste excess is exctreted via the anal pore.

Paramecium also use trichocysts which protrude from the cell as a defence mechanism to help protect themselves from predators.[1]

A Paramecium cell has two nuceli, the germinal nucleus also known as the micro-nucleus is involved in sexual processes. Fundamentally the transfer of genetic information; meiosis is conducted as this nucelus. The somatic nucleus, also known as the macro-nucleus participates in the process of transcription and ensures expression of genetic information.

Paramecium lives in a freshwater environment which in the abscence of contractile vacuoles would burst this is caused by the osmotic uptake of water, by a process known as osmoregulation [2]. Near to the cell surface membrane, contractile vacuoles have canals and these take up water from the cytoplasm and carry it to the vacuole. The pore opens and the vacuole contracts expelling the water. Within close proximity of the contractile vacuoles are many mitochondria and this is due to the face that the organelles require ATP as its source of energy.

The Paramecium cell reproduces by a process called conjugation [3] and asexual fission.   Asexual fission creates two genetically identical daughter cells.

Paramecium has action potentials not unlike those that occur in neurons.  However, in Paramecium, calcium ions enter the cell through voltage gated channels and cause the rapid depolarisation of the membrane[4] and generate an action potential, rather than the sodium ions (as in neurones). The repolarising phase is due to the closing of the calcium ion channels and the opening of the potassium ion channels [5].

The length of a typical paramecium varies from 100 μm to 300 μm [6]. They can be found in freshwater areas, like riveres, ponds and lakes [7].

Paramecium cells are capable of regulated exocytosis when triggered by an external stimulus. This exocytosis is similar to the release of neurotransmitters by the presynaptic membrane at a synapse. However instead of using it for signalling and depolarising the postsynaptic membrane, it is used as a defence mechanism against predators [8][9].


  1. Beale, Geoffrey (2008) Paramecium Genetics and Epigentics CRC Press, Taylor and Fancis Group, Pg 23
  2. Beale, Goffey and Preer, John R. Jr. (2008) Paramecium Genetics and Epigenetics CRC Press, Taylor and Francis Group.
  3. L.Prescott, J.Hardley and D.Klein Microbiology 6th Edition New York:McGraw-Hill
  4. Hinrichsen, R. and Schultz, J. (1988) “Paramecium: a model system for the study of excitable cells” Trends in Neurosciences, vol 11, no. 1, pp. 28
  5. Eckert, R. and Brehm, P. (1979) Ionic Mechanisms of Excitation in Paramecium. Annual Review of Biophysics and Bioengineering. 8, 353-383
  6. Brock Biology of Micro-organisms 12th Edition, Madigan Dunlap Clark, Pg 69
  7. Holtzman E, Novikoff A (1984) Cells & Organelles, 3rd edition, USA, CBS College Publishing
  8. Genoscope (2007) Paramecium tetraurelia: Paramecium, a model ciliate
  9. Wincker P (1st November 2006) Nature 444 171-178 Global trends of the whole-genome duplications revealed by the ciliate Paramecium tetraurelia 29th November 2012
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