Back in the late 70-ies of the XIX century in the retina of animalrsquo;s eyes and then in humanrsquo;s scientists have discovered the light-sensitiv

Visual pigments (opsins: rhodopsin and iodopsin)

Back in the late 70-ies of the XIX century in the retina of animal’s eyes and then in human’s scientists have discovered the light-sensitive pigments, which become discolored in the light. The rods contain rhodopsin (from Greek “a rose” and “a vision”), and cones — iodopsin (diagram 175). Both pigments are high molecular weight compounds that consist of oxidized vitamin A — retinal and opsin protein.

In the darkness rhodopsin and iodopsin are in an inactive form. Under the influence of light, they decompose (“fade”) and switch to the active form: retinal cleaves from the opsin. As a result, the photoreceptors excite. A nerve impulse occurs. In the darkness the visual pigments recover due to the merge of vitamin A (retinal) with opsin. Lack of vitamin A in the diet causes frustration of chopsticks and a violation of dusky view — the "night blindness": human almost cannot see anything in the evening, and the day sight is functioning normally. That is why it is important to eat foods containing vitamin A. Taken from http://worldofschool.org

Diagram 175. The photosensitive pigment rhodopsin (a) and its transformations (b) under the action of light and in darkness
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  • What is the day and the dusky vision?