Photochemistry of Vision

Photochemistry of Vision

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Radiation can only affect matter if absorbed by it. Within the broad range of 300-1000 nm, which we call qthe visibleq, light quanta are energetic enough to produce excited electronic states in the atoms and molecules that absorb them. In these states the molecules may have quite different properties from those in their dormant condition, and reactions that would not otherwise occur become possible. About 80 % of the radiant energy emitted by our sun lies in this fertile band, and so long as the sun's surface temperature is maintained at about 6000Ad C this state of affairs will continue. This and the transparency of our atmosphere and waters have allowed the generation and evolution of life. Before life began the atmosphere probably also transmitted much of the solar short-wave radiation, but with the rise of vegetation a new product - oxygen - appeared and this, by a photochemical reaction in the upper atmosphere, led to the ozone layer that now protects us from the energetic qshort-waveq quanta that once, perhaps, took part in the generation of life-molecules. Light is an ideal sensory stimulus. It travels in straight lines at great speed and, consequently, can be made to form an image from which an animal can make qtrueq, continuous and immediate assessments of present and impending events.... European red (see Sciurus vulgaris) a€“ flying (see Glaucomys volans) a€” grey ( see Sciurus carolinensis) a€“ ground (see Citellus) 339a€“342 ... 514 Stiles- Helmholtz line element 595, 596 Stizostedion vitreum (walleye) 270 Streptopelia risoria (ringneck dove) 618 Strix (owl) ... Temperature, low (see Low temperature) Temperature tolerance, fishes 441 Template curve (see Nomogram) Tench (see Tinca sp.)anbsp;...

Title:Photochemistry of Vision
Author: Herbert J.A. Dartnall
Publisher:Springer Science & Business Media - 2012-12-06

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