what is one reason why plants have accessory pigment molecules like chlorophyll b and carotenoids?
They have different absorption maxima to chlorophyll a and so these accessory pigments make light absorption more efficient by absorbing some wavelengths not absorbed by chlorophyll a and thus provide a greater input of light into the reaction centres.
Chlorophyll actually speaking does'nt give the green color to the plant.It reflects the green wavelength and hence the green color.There are other pigments present in the leaf like chlorophyll a , chlorophyll b,c,d and e.Chlorophyll a is the primary pigment.It reflects the green,red and blue wavelength.It consitutes the reaction center in the chloroplasts which absorbs all the light incident on the leaf which in turn facilitates photosynthesis.Then there is Xanthophyll and carotene.Xanthophyll is orange yellow in color.Carotene is orange in color.Xanthophyll and Carotene are called as the accessory pigments present in the leaf.They reflect the blue, red and violet wavelength.I hope this info is sufficient.
Pigments in plant biology are actually (as you may know) long-chain conjugated systems which absorb light at specific frequencies. This specificity is largely due to the morphological and physical features of each pigment molecule. Since Chlorophyll a only absorbs well at wavelengths of about 400-450 nm and 650-700 nm a plant empowered with only this photosynthetic molecule would have an extremely limited range of spectral absorption. This is where the accessory pigments come in. Chlorophyll b's absorption peaks at 450-500 nm and 600-650 nm and Xanthophyll's at around 400-530 nm, allowing for a much wider absorption range. Carotenes contribute to photosynthesis by transmitting the light energy they absorb from chlorophyll back into the energetic system. None of the pigments, absorb well in the green-yellow region which is largely responsible for the abundance of greens we see throughout nature. The five main pigments are: Chlorophyll a - a blue-green pigment Chlorophyll b - a yellow-green pigment Carotene - an orange pigment Xanthophyll - a yellow pigment Phaeophytin a - a gray-brown pigment Phaeophytin b - a yellow-brown pigment A good illustration of this concept can be found in this graph of Photosynthetically Active Radiation, illustrating the absorption peaks of all the molecules: upload.wikimedia.org/wikipedia/co...
