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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.
The eyespot is located near the cell equator. It is composed of a carotenoid-rich granule layer in the chloroplast which act like a light reflector. [6] The main function of the eyespot is the phototaxis, which consist of the movement (with the flagella) related to a light stimulus. [7]
It possesses an eyespot, a small area highly sensitive to light, [41] [42] which triggers the two flagella differently. [43] Those responses are adaptive, on a timescale matched to the rotational period of the cell body, [ 44 ] [ 45 ] [ 46 ] and allow cells to scan the environment and swim toward light. [ 47 ]
Euglena is a genus of single cell flagellate eukaryotes.It is the best known and most widely studied member of the class Euglenoidea, a diverse group containing some 54 genera and at least 200 species.
It has forward and backwards movement, as well as changes in its direction. Additionally, E. gracilis contains a light-sensitive eyespot, or stigma, which enables it to exhibit phototaxis by moving towards light sources for photosynthesis. The cell also possesses a contractile vacuole responsible for osmoregulation, helping maintain proper ...
The retina adapts to change in light through the use of the rods. In the dark, the chromophore retinal has a bent shape called cis-retinal (referring to a cis conformation in one of the double bonds). When light interacts with the retinal, it changes conformation to a straight form called trans-retinal and breaks away from the opsin.
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The secondary eyes have a reflector at the back of the eyes. The light-sensitive part of the receptor cells is next to this, so they get direct and reflected light. In hunting or jumping spiders, for example, a forward-facing pair possesses the best resolution (and even some telescopic ability) to help spot prey from a distance.