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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.
Ocelli (the plural of ocellus) are a type of simple eye, or eyespot. They are photoreceptive, but very simple; differing from complex eyes with compound lenses, ocelli cannot morph the sensation of light into a complete image, and are utilized to sense movement and the absence and presence of light.
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 ]
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.
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
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. The size of the pupil, which controls the amount of light entering the eye, is adjusted by the iris' dilator and sphincter muscles.
The basic light-processing unit of eyes is the photoreceptor cell, a specialized cell containing two types of molecules bound to each other and located in a membrane: the opsin, a light-sensitive protein; and a chromophore, the pigment that absorbs light. Groups of such cells are termed "eyespots", and have evolved independently somewhere ...