. Biological effects of radiation; mechanism and measurement of radiation, applications in biology, photochemical reactions, effects of radiant energy on organisms and organic products. Radiation; Biology. 500 428 375 "*" Wcjve Lengths in mfi. Fig. 3.—Absorption curves in benzene of A, chlorophyll a; B, chlorophyll b. {Winterstein and Stein, 145.) Of primary importance is the question as to what pigments are of sig- nificance for the photosynthetic reaction. This question can be partially answered by a comparison of the absorption spectra of the photosyn- thetic organs and of the pig
. Biological effects of radiation; mechanism and measurement of radiation, applications in biology, photochemical reactions, effects of radiant energy on organisms and organic products. Radiation; Biology. 500 428 375 "*" Wcjve Lengths in mfi. Fig. 3.—Absorption curves in benzene of A, chlorophyll a; B, chlorophyll b. {Winterstein and Stein, 145.) Of primary importance is the question as to what pigments are of sig- nificance for the photosynthetic reaction. This question can be partially answered by a comparison of the absorption spectra of the photosyn- thetic organs and of the pigments themselves with the activity of different wave- lengths of light of the same incident intensity. In order to avoid the influence of the physical structure of the leaf on the determination of the absorp- tion spectra of leaf pigments many investigators have used extracts of the leaf pigments in organic solvents. In general these solutions show the same type of absorption curve as the leaves themselves, which are characterized by strong absorption in the red and violet and high transmission in the green. In acetone and alcohol extracts of leaves the absorption curves are shifted toward the violet as compared with the absorption curves of the living leaves, Fig. 1. The narrow absorption bands character- istic of pure chlorophyll solu- tions are not evident in the absorption curves of leaves. On the basis of chromato- graphic adsorption ex- periments the principal chloroplast pigments are: chlorophyll a, chlorophyll h, a- and /3-carotene, and the xanthophylls (144). The pig- ment content of leaves varies with the conditions under which the leaves are obtained. On the basis of percentage dry weight the amount of chlorophyll is greater for shade than for sun plants, whereas the amount of yellow. 700 800 500 600 Wave Length in mfi Fio. 4.—Absorption curves in ether of A, chloro- phyll o; B, chlorophyll b. (Zscheile, 153.) pigment is approximately the same (14
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