Euglena is commonly studied in biology classes because it has both plant (it has chloroplasts and so can photosynthesise) and animal (it moves and can eat) characteristics. Depending on conditions, photosynthesis or eating can predominate. It is a single celled creature (a PROTIST) with a large flagellum that lives in fresh water. It is generally elongate but can change its shape quite dramatically during so-called euglenoid movement. It swims using its flagellum and can orientate itself with respect to gravity and light. It is a common laboratory species.
Euglena Structure: Euglena has a spiralised outer pellicle visible in this graphic as a helical surface reflection. At the anterior of the organism, the surface invaginates forming a canal which expands into a reservoir. Emerging from the reservoir is a long flagellum (there is a smaller secondary flagellum that does not reach the exterior). Attached to the major flagellum is the paraxonemal body which is light sensitive. Partially shading it (and in so doing providing orientation with respect to the light source) is the red eye spot or stigma. Near the reservoir lies the contractile vacuole which expels excess water into the reservoir (a process called osmoregulation). Chloroplasts are dotted througout the cell, their positions optimised to collect the most light. These chloroplasts were originally free living creatures that were incorporated in the distant past. The chloroplasts have characteristic pyrenoids. Starch is stored as paramylon. Paramylon reserves are shown as pale straw coloured bodies. There is a nucleus with a distinct nucleolus.
August 8th, 2012
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