The most significant difference between primary and accessory pigments is that they absorb and give off light at different wavelengths.
When photons of light hit a leaf, they have a specific wavelength. Chlorophyll has a specific wavelength that it can absorb and give off light as. If chlorophyll was the only pigment a plant had, it could only use light that was of this particular wavelength. However, the presence of accessory pigments allows the plant to use light of all wavelengths.
Primary and accessory pigments also vary in color. Chlorophyll is green, while others are different. Carotenoids can be red, yellow or orange. Photosynthetic aquatic organisms like cyanobacteria also have phycobilins.
1. Primary pigments:
primary pigments In photosynthesis, pigments that emit electrons which directly drive the photosynthetic reactions.
In green plants there are two primary pigments,
both of which are forms of Chorophyll a: P680 and P700.
2. Accessory pigments:
a pigment in plants that can absorb light energy and pass the electrons along to the primary pigment which starts the process of photosynthesis.
In the flowering plants (angiosperms),
chlorophylls a and b provide the green color and absorb the light energy needed for photosynthesis.
However, other accessory pigments, such as yellow xanthophylls and orange carotenes are also present in the chloroplasts and collect additional light energy for photosynthesis.
All plants, algae, and cyanobacteria which photosynthesize contain chlorophyll "a".
A second kind of chlorophyll is chlorophyll "b", which occurs only in green algae and in the plant.
Carotenoids act as \"SHIELD PIGMENTS\" as they are located over the chlorophylls thus protecting them from photo-oxidation and photo-bleaching. (antioxidants)
Phycobilins are water-soluble pigments, and are therefore found in the cytoplasm, or in the stroma of the chloroplast. They occur only in Cyanobacteria and Rhodophyta.
Bonded to certain water-soluble proteins, ‘Phycobiliproteins’ then pass the light energy to chorophyll for photosynthesis.
The phycobilins are especially efficient at absorbing red, orange, yellow and green light, wavelengths which are not well absorbed by chlorophyll a. Organisms growing in shallow waters tend to contain phycobilins that can capture yellow/red light, while those at greater depth often contain more of the phycobilins that can capture green light, which is relatively more abundant there.
