Absorption & Action Spectra
- Chloroplasts contain several different photosynthetic pigments within photosystems embedded in the thylakoid membranes
- Different pigments absorb light of different wavelengths
- Chlorophylls absorb wavelengths in the blue-violet and red regions of the light spectrum, reflecting green light and appearing green in colour
- Carotenoids absorb wavelengths of light mainly in the blue-violet region of the spectrum, reflecting yellow and orange light
- Carotenoids often remain in leaves after the breakdown of chlorophyll in the autumn, giving some leaves their yellow, orange, and red autumn colours
Examples of Photosynthetic pigments Table
| Pigment group | Name of pigment | Colour of pigment |
| Chlorophylls | Chlorophyll a | Blue-green |
| Chlorophyll b | Yellow-green | |
| Carotenoids | β Carotene | Orange |
| Xanthophyll | Yellow |
- The amount of light at different wavelengths absorbed by a particular pigment gives that pigment's absorption spectrum (plural spectra)
- Because each type of pigment absorbs light at different wavelengths the absorption spectrum of each pigment is different
Different photosynthetic pigments absorb light of different wavelengths, giving different absorption spectra
- A plant's rate of photosynthesis varies depending on the wavelengths of light available
- The changing rate of photosynthesis at different wavelengths is known as an action spectrum
- Action spectra are very closely correlated to the absorption spectra of the different pigments
- Having several different pigments with different absorption spectra allows plants to photosynthesise under a wider variety of light wavelengths; this extends the action spectra of plants and maximises rates of photosynthesis
Plant action spectra are closely related to the absorption spectra of the different photosynthetic pigments
