. Principles of modern biology. Biology. Fig. 9-2. Chloroplast of a corn plant: electronmicrograph with a total magnification of about 24,000. Chloro- phyll is restricted to the grana (one granum encircled). The form of a granum, in three dimensions, is suggestive of a stack of coins. The several grana are suspended in the chloroplast by strands of material, called stroma. (Courtesy of A. E. Vatter, University of Colorado, Medical Center.) of the granum (Fig. 9-3). Precise measure- ments of the thickness of each lamella and of the density of the components indicate that the layers of chlorophy
. Principles of modern biology. Biology. Fig. 9-2. Chloroplast of a corn plant: electronmicrograph with a total magnification of about 24,000. Chloro- phyll is restricted to the grana (one granum encircled). The form of a granum, in three dimensions, is suggestive of a stack of coins. The several grana are suspended in the chloroplast by strands of material, called stroma. (Courtesy of A. E. Vatter, University of Colorado, Medical Center.) of the granum (Fig. 9-3). Precise measure- ments of the thickness of each lamella and of the density of the components indicate that the layers of chlorophyll are regularly flanked. Fig. 9-3. Single granum at higher magnification (about 160,000). This reveals the lamellar structure. A thin layer of chlorophyll lies between the two mem- branes in each lamella, and the lamellar membranes appear to be made up of protein and lipid compo- nents. (Courtesy of A. E. Vatter, University of Colo- rado, Medical Center.) by layers of protein and of a speciali/ed lipid material. In any event, the fine structural or- ganization of the grana and of the other parts of the chloroplast provides an amazingly effective molecular mechanism for utilizing light energy. This mechanism permits chloro- phyll, working in partnership with various other enzymes and coenzymes, to transform and conserve light energy in the form of or- ganic compounds newly synthesized from in- organic forms of matter. Some Modern Developments. Since 1905, starting with the work of a British botanist, F. F. Blackman, it has been known that the synthesis of carbohydrates and other organic compounds by green plants must involve two separable kinds of reactions: (1) light reac- tions, an exceedingly rapid set of reactions that are energized by light; and (2) dark re- actions, a series of slower reactions that can proceed in the absence of light. But truly im- pressive progress in the field of photosyn-. Please note that these images are extracted from scanned page images that may h
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