Examples of unicellular organisms

What are unicellular organisms

Organisms constituted by a single cell , in general they are called microorganisms and they are living beings that fulfill all the vital functions such as growing, reproducing , feeding , reacting to stimuli from the environment, etc. As examples we have bacteria , some microscopic algae , some protozoan fungi , etc.

Unicellular organisms have colonized practically all the environments of the planet , and they have evolved  biochemically versatile and structurally complex. However, the cell has an important limitation of size. The small size is an imposition for the cell. An increase in size means that the surface in contact with the external environment is smaller in relation to the volume, and this leads to problems when obtaining nutrients and eliminating waste, even for an efficient communication internal . An alternative to the increase in cell size has been the grouping of cells to form larger organisms (multicellular organisms). Initially in a simple association of cells, and finally in an organized, hierarchical and highly specialized society of cells.


We also consume dietary supplements based on algae, for example, or we apply cosmetic products that are obtained from them.

All living beings  present different degrees of complexity in terms of their internal structure or organization, which is why we have:

  • Superior organisms :  They are characterized by presenting organs and tissues , the latter are composed of numerous specialized cells , and the cells of different tissues have some differential characteristics.
  • Lower organisms :  They are much simpler in structure , to such an extent that sometimes they are composed only of an undifferentiated cell: these organisms are known as unicellular organisms.

In the latter, all vital functions depend on that single cell , which can be prokaryotic (with free nuclear material in the cytoplasm) or eukaryotic (with the nuclear material encased in the nuclear membrane). That single cell self-regulates and directs all vital functions.



Obviously unicellular organisms cannot be seen with the naked eye (since a cell is always something very small), but with microscopes.

The fact of being such small individuals supposes a series of advantages:

  • The high surface / volume ratio , which facilitates contact with the external environment and, therefore, nutrition.
  • Having cell compartments very close , which contributes to their typical accelerated metabolism and the rapid rate of reproduction that characterizes them.


In general they reproduce by bipartition (cell division), some can also present budding and sporulation phenomena , all these processes are based on mitosis.

Many unicellular beings are grouped forming colonies . In the case of bacteria , which are unicellular, outside the cell there is an additional structure called the wall, which has important functions.

We can find unicellular organisms in three of the five kingdoms in which living beings are divided:

  • Monera : Kingdom represented by bacteria and in which all its members are unicellular.
  • Protista : Only some members are.
  • Fungi : Only the yeasts are unicellular


41 examples of unicellular bacteria:

1. Acetobacter aurantius
2. Acinetobacter baumannii
3. Actinomyces Israelii
4. Agrobacterium radiobacter
5. Agrobacterium tumefaciensAzotobacter vinelandii
6. Anaplasma
7. Bacillus anthracis
8. Bacillus brevis
9. Bacillus cereus
10. Bacillus fusiformis
11. Bacillus licheniformis
12. Bacillus megaterium
13. Bacillus mycoides
14. Bacillus stearothermophilus
15. Bacillus subtilis

16. Enterococcus avium
17. Enterococcus durans
18. Enterococcus faecalis
19. Enterococcus faecium
20. Enterococcus galllinarum
21. Enterococcus maloratus
22. Stayyereyofhia mioms
23. Streptococcus agalactiae
24. Streptococcus avium
25. Streptococcus bovis
26. Streptococcus cricetus
27. Streptococcus faceium
28. Streptococcus faecalis
29. Streptococcus ferus
30. Streptococcus gallinarum
31. Streptococcus lactis
32. Streptococcus mitior
33. Streptococcus mitis
34. Streptococcus oralis
35. Streptococcus pneumoniae
36. Streptococcus pyogenes
37. Streptococcus rattus
38. Streptococcus salivarius
39. Streptococcus sanguis
40. Smreptococcus mutans
41. Streptococcus sobrinus

26 examples of unicellular organisms protozoa:

1. Apostomatia
2. Astomatia
3. Chonotrichia
4. Choreotrichia
5. Colpodea
6. Haptoria
7. Heterotrichea
8. Hymenostomatia
9. Hypotrichia
10. Karyorelictea
11. Litostomatea
12. Nassophorea
13. Oligohymenophorea
14. Oligotrichia
15. Peniculy
16. Peritrichia
17. Phyllopharyngea
18. Phyllopharyngia
19. Plagiopylea
20. Prostomatea
21. Rhynchodia
22. Scuticociliatia
23. Spirotrichea
24. Stichotrichia
25. Suctoria
26. Trichostomatia

5 examples of unicellular algae:

1. Chrysophytes
2. Noctiluca
3. Dinoflagellates
4. Eugleophytes
5. Diatoms.

5 examples of unicellular fungi:

1. Cladosporium
2. Penicillium
3. Alternaria
4. Aspergillus
5. Mucor

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