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Schematic representation of a Euglena cell with red eyespot (9) Schematic representation of a Chlamydomonas cell with chloroplast eyespot (4). The eyespot apparatus (or stigma) is a photoreceptive organelle found in the flagellate or (motile) cells of green algae and other unicellular photosynthetic organisms such as euglenids.
Euglena divide longitudinally, beginning at the front end of the cell, with the duplication of flagellar processes, gullet and stigma. Presently, a cleavage forms in the anterior , and a V-shaped bifurcation gradually moves toward the posterior , until the two halves are entirely separated.
Euglena gracilis is a freshwater species of single-celled alga in the genus Euglena. It has secondary chloroplasts , and is a mixotroph able to feed by photosynthesis or phagocytosis . It has a highly flexible cell surface, allowing it to change shape from a thin cell up to 100 μm long to a sphere of approximately 20 μm.
They are insufficient for vision, as they cannot distinguish shapes or determine the direction light is coming from. Eyespots are found in nearly all major animal groups, and are common among unicellular organisms, including euglena. The euglena's eyespot, called a stigma, is located at its anterior end. It is a small splotch of red pigment ...
The stigma is located laterally, in a fixed plane relative to the cilia, but not directly adjacent to the basal bodies. [62] [63] The fixed position is ensured by the attachment of the chloroplast to one of the ciliary roots. [64] The pigmented stigma is not to be confused with the photoreceptor.
The stigma is located laterally, in a fixed plane relative to the cilia, but not directly adjacent to the basal bodies. [42] [43] The fixed position is ensured by the attachment of the chloroplast to one of the ciliary roots. [44] The pigmented stigma is not to be confused with the photoreceptor.
The red eyespot of a euglena filters light for the photoreceptor so that only certain wavelengths of light are able to reach the photoreceptor, allowing the euglena to “steer” itself by moving toward light in different intensities in different areas of its photoreceptor. Key: 1. Microtubules that make up the pellicle (see 9.) 2.
Euglenales consists mostly of freshwater organisms, in contrast to its sister Eutreptiales which is generally marine. Cells have two flagella, but only one is emergent; the other is very short and does not emerge from the cell, so cells appear to have only one flagellum. [3]