Cells Living in Cells

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Enzyme: a protein that changes the speed of chemical reactions.

Unicellular: living things that only have one cell such as bacteria... more

Endosymbiosis: Living Together

When two or more species share a close physical interaction, we call this a symbiosis.  We share symbioses with many different species. For example, living in our guts are millions and millions of bacteria cells. They live inside us in a symbiotic relationship, from which we both benefit. We benefit from our gut bacteria because they have enzymes that can digest food particles that we cannot. Our gut bacteria benefit from us as they get a place to live (our gut), and a share of some of the nutrients from the food we eat.


Endosymbiosis is a special kind of symbiosis. It’s when one organism lives within the cells or tissues of another. Endosymbioses are very common among unicellular organisms. In the video above, you can see a unicellular organism called Paramecium bursaria (eukaryotic). Within it are many green spheres. Those green spheres are completely separate organisms; they're green algae cells (also eukaryotic) called Chlorella

The algae are living endosymbiotically within the paramecium. The algae help the paramecium to survive by sharing with it some of the energy they produce by harvesting sunlight. The paramecium provides a safe, mobile home for the algae to live in. 

Video by Sally Warring. Additional images via Wikimedia Commons. Plant cells with chloroplasts by Des_Callaghan.

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Bibliographic details:

  • Article: Endosymbiosis: Living Together
  • Author(s): Sally Warring
  • Publisher: Arizona State University School of Life Sciences Ask A Biologist
  • Site name: ASU - Ask A Biologist
  • Date published: February 24, 2016
  • Date accessed: March 27, 2023
  • Link: https://askabiologist.asu.edu/endosymbiosis-living-together

APA Style

Sally Warring. (2016, February 24). Endosymbiosis: Living Together. ASU - Ask A Biologist. Retrieved March 27, 2023 from https://askabiologist.asu.edu/endosymbiosis-living-together

American Psychological Association. For more info, see http://owl.english.purdue.edu/owl/resource/560/10/

Chicago Manual of Style

Sally Warring. "Endosymbiosis: Living Together". ASU - Ask A Biologist. 24 February, 2016. https://askabiologist.asu.edu/endosymbiosis-living-together

MLA 2017 Style

Sally Warring. "Endosymbiosis: Living Together". ASU - Ask A Biologist. 24 Feb 2016. ASU - Ask A Biologist, Web. 27 Mar 2023. https://askabiologist.asu.edu/endosymbiosis-living-together

Modern Language Association, 7th Ed. For more info, see http://owl.english.purdue.edu/owl/resource/747/08/

Chloroplasts found in plant and algae cells evolved from cyanobacteria that were able to live in other cells unharmed.

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