Communication Topic 7: Visual Pigments. Biology in Focus, HSC Course Glenda Childrawi , Margaret Robson and Stephanie Hollis. DOT Point(s) . outline the role of rhodopsin in rods
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Biology in Focus, HSC Course
Glenda Childrawi, Margaret Robson and Stephanie Hollis
All rods have only one type of pigment, rhodopsin. They are not sensitive to different colours.
Cones contain one of three types of iodopsin pigments and are most sensitive to light in one of three wavelengths. These pigments result in cone cells being sensitive to:
However, the sensitivity of a particular cone cell allows it to detect light to some extent on either side of these peak sensitivities, giving it an overlap in some of the colours detected. ‘Red’ cones are actually more sensitive to yellow light (560-565nm) than to red light, but they respond to red light before any of the others do, therefore behave as red receptors.
By comparing the rate at which various receptors respond, as well as the overlap in colours detected, the brain is able to interpret these signals as intermediate colours..
The visual pigment rhodopsin, present in rods, consists of a protein molecule, opsin, combined with a simple, light absorbing part called retinal.
The main function of the photochemical pigments rhodopsin is to absorb light.
The split rhodopsin pigment is said to be ‘bleached’, but this change is temporary.
The signal is termed electrochemical because it involves both an electrical change in membrane and a chemical release of a neurotransmitter. The bipolar cell transmits the electrochemical signal to the ganglion cells which in turn carry the signal to the brain.
Retinal and opsin recombine with the help of enzymes. This allows a new image to be received. The presence of vitamin A is essential for these steps to occur.
-Students to complete DOT Point 4.6 Photoreceptor cells in mammals, insects and another animal