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Unformatted text preview: shape of the pigment molecules. This process leads to electrical changes in the receptor membrane that in turn lead to the propagation of a nerve signal. In some animals, such as the earthworm, photoreceptors are scattered over the skin. Usually, however, photoreceptors are clustered together to form an eye. Primitive eyes detect only the presence or absence of light. In the more advanced vertebrate eye, there are two types of receptors: rods and cones. Rods are elongated and sensitive to low levels of illumination. This vision is colorless and has poor definition. Rods are predominant in nocturnal animals, for which increased sensitivity is important. Cones are sensitive to high levels of illumination and produce a sharp picture. Unlike rods, cones contain more than one type of photopigment, each sensitive to different wavelengths of light. Cones provide color vision....
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This note was uploaded on 01/27/2012 for the course BIOLOGY BSC1005 taught by Professor Rodriguez during the Winter '09 term at Broward College.
- Winter '09