School of Life Sciences | Ask A Biologist

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Endosymbiosis

Endosymbiosis: Living Together

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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.
Plant cells with chloroplasts

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

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Plant cells with chloroplasts

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

Share to Google Classroom

Be part of Ask A Biologist

by volunteering, or simply sending us feedback on the site. Scientists, teachers, writers, illustrators, and translators are all important to the program. If you are interested in helping with the website we have a Volunteer page to get the process started.