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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 main function of the eyespot is the phototaxis, which consist of the movement (with the flagella) related to a light stimulus. [7] The phototaxis is crucial for the alga and allows for localization of the environment with optimal light conditions for photosynthesis. [8] Phototaxis can be positive or negative depending on the light intensity ...
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 ...
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.
Retinylidene proteins, or rhodopsins in a broad sense, are proteins that use retinal as a chromophore for light reception. They are the molecular basis for a variety of light-sensing systems from phototaxis in flagellates to eyesight in animals. [1] Retinylidene proteins include all forms of opsin and rhodopsin (in the broad sense).
At the heart of a photosystem lies the reaction center, which is an enzyme that uses light to reduce and oxidize molecules (give off and take up electrons). This reaction center is surrounded by light-harvesting complexes that enhance the absorption of light. In addition, surrounding the reaction center are pigments which will absorb light. The ...
The blue-light sensitive ChR2 and the yellow light-activated chloride pump halorhodopsin together enable multiple-color optical activation and silencing of neural activity. [ 64 ] [ 65 ] Another interesting pair is the blue-light sensitive chloride channel Gt ACR2 [ 66 ] and the red-light sensitive cation channel Chrimson [ 67 ] which have been ...