Colour vision in humans relies on three types of cones in...

Colour vision in humans relies on three types of cones in the retina of the eye, and these absorb light at wavelengths of about 445,530 and $565 \mathrm{nm} .$ (a) To what colours do these wavelengths correspond? (b) Do you expect plots of absorbance against wavelength for each absorption to be sharp or broad? Give reasons for your answer. (c) The colour vision of the honeybee (Apis mellifera) depends on three visual pigments which absorb at 344,436 and $556 \mathrm{nm} .$ To which regions of the spectrum do these wavelengths correspond?

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Key Concepts

Colour Vision Mechanism

Colour vision is the ability to perceive differences in wavelength due to the presence of multiple types of photoreceptor cells in the retina, each sensitive to different wavelength ranges. This mechanism allows animals to differentiate and interpret various colours based on the relative stimulation of these receptors.

Photoreceptor Absorption Spectra

The absorption spectra of photoreceptors are typically broad rather than narrow, meaning each type of photoreceptor responds to a range of wavelengths rather than an isolated single wavelength. This broadness is due to the molecular structure of the photopigments and the interactions among multiple vibrational and electronic transitions within the molecules.

Comparative Visual Systems in Different Species

Different species have evolved visual systems adapted to their specific environmental needs, leading to variations in the types and peak absorption wavelengths of photoreceptors. For instance, while one species might have pigments peaking at wavelengths that cover what humans perceive as blue, green, and red, another may extend sensitivity into ultraviolet ranges, thereby enabling them to see patterns or signals not visible to the human eye.

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