Photosynthetically active radiation the predominance of chlorophyll is autumn, when chlorophyll is degraded (because it contains N and Mg) but the accessory pigments are not (because they only contain C, H and O) and remain in the leaf producing red, yellow and orange leaves. In land plants, leaves absorb mostly red and blue light in the first layer of photosynthetic cells because of Chlorophyll absorbance. Green light, however, penetrates deeper into the leaf interior and can drive photosynthesis more efficiently than red light. Because green and yellow wavelengths can transmit through chlorophyll and the entire leaf itself, they play a crucial role in
Photosystem I when they become photoexcited. Antenna molecules can absorb all wavelengths of light within the visible spectrum. The number of these pigment molecules varies from organism to organism. For instance, the cyanobacterium "Synechococcus elongatus" ("Thermosynechococcus elongatus") has about 100 chlorophylls and 20 carotenoids, whereas spinach chloroplasts have around 200 chlorophylls and 50 carotenoids. Located within the antenna complex of PSI are molecules of chlorophyll called P700 reaction centers. The energy passed around by antenna molecules is directed to the reaction center. There may be as many as 120 or as few as 25 chlorophyll molecules per P700. The P700 reaction center