Euglena - part plant, part animal

Cells with a nucleus are called true cells, or eukaryotes, which can be further subdivided into kingdoms like plant and animal. Plant cells and animal cells are different in their components and structure, but some organisms does not fit as neatly into these little boxes and can be tricky to place on ‘the tree of life’. One of these is the single celled organism euglena.

Euglena with clearly visible red eyespots

Euglenas are part animal and part plant. They get their green coloration from chloroplasts and are thereby able to acquire food by photosynthesis like plants. But euglenas are also able to acquire nutrients from their environment, like animals. So, this organism drifts around between kingdoms, and is sometimes even placed in its own little corner of the phylogenetic tree. However, what we do know is that euglenas are flagellates, which mean they have a thin and long whip-like appendage, a flagellum, used for movement. In the front of the cell is a red spot. This is a very primitive eye, enabling the organism to sense light direction and intensity. This comes in very handy when trying to find the optimal place for photosynthesis and utilize its chloroplasts.

These organisms like nutrient rich waters, but if conditions become unfavorable they are able to transform into a resting cyst called a palmelloid stage. This looks like a ball because the cell swells up. In this stage the cell loses its flagellum and starts to produce large amounts of mucus. This mucus encases the cell and protects it until conditions improve.

In the clip below you are able to see active as well as cyst stages of euglena.

Euglenas at different magnifications illuminated with different techniques. 

10x, 20x, 40x, & 60x - modified brightfield, simple brightfield, and darkfield