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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. It allows the cells to sense light direction and intensity and respond to it, prompting the organism to either swim towards the light (positive phototaxis ...
The posterior chamber constitutes the remaining five-sixths; its diameter is typically about 24 mm (0.94 in). An area termed the limbus connects the cornea and sclera. The iris is the pigmented circular structure concentrically surrounding the centre of the eye, the pupil, which appears to be black.
Eyespot (mimicry), a color mark that looks somewhat like an eye; Eyespot, a sensory organ of invertebrates; see simple eye in invertebrates; Eyespot, a type of eye in some gastropods, a part of sensory organs of gastropods; Eyespot apparatus, a photoreceptive organelle found in the flagellate (motile) cells unicellular photosynthetic organisms
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 ]
The structure of the mammalian eye owes itself completely to the task of focusing light onto the retina. This light causes chemical changes in the photosensitive cells of the retina, the products of which trigger nerve impulses which travel to the brain. In the mammalian eye, light enters the pupil and is focused on the retina by the lens.
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 ]
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The thin overgrowth of transparent cells over the eye's aperture, originally formed to prevent damage to the eyespot, allowed the segregated contents of the eye chamber to specialise into a transparent humour that optimised colour filtering, blocked harmful radiation, improved the eye's refractive index, and allowed functionality outside of water.