How does light affect the distribution of Euglena sp. and Tetrahymena pyriformis

(1) Milton Academy, Milton, Massachusetts
Cover photo for How does light affect the distribution of <em>Euglena sp.</em> and <em>Tetrahymena pyriformis</em>

The broad range of energy sources utilized by organisms to obtain organic molecules from their environment include plants, animals, and sunlight. Differences in migration patterns and anatomy can often be attributed to these differing energy sources across organisms. To evaluate the distribution patterns of organisms Euglena sp. (Euglena) and Tetrahymena pyriformis (T. pyriformis) both organisms were treated with light. Euglena is a genus of more than 1,000 species consisting of single-celled flagellates that primarily live in freshwater and saltwater, and T. pyriformis is a single-celled, ciliated eukaryote that typically inhabits fresh water. Tubes filled with either T. pyriformis or Euglena were exposed to three different treatments: entirely to light, entirely to darkness, or exposed on one half to light and the other half to darkness. Results show that Euglena exhibited a phototactic response to light, as there was a statistically significant 17 organism increase on the side exposed to light and an 8 organism decrease on the side exposed to darkness after the 30-minute period. T. pyriformis did not show any significant redistribution after exposure to any of the treatments. Due to T. pyriformis’s heterotrophic nature and Euglena’s autotrophic nature, these findings were most likely the result of characteristics that aid Euglena as autotrophs and are absent in T. pyriformis. Specifically, Euglena have a red eyespot that locates areas of light and chloroplasts. Red eyespots and chloroplasts are two of the many photosynthetic organelles that facilitate the process of photosynthesis in areas of light, making lighted areas optimal for the survival of Euglena in comparison to areas of darkness.

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