. Principles of modern biology. Biology. Nutrition of Green Plant Cells - 159 mediary stages. Nevertheless it was many years before even this much information be- came available. The first inkling that photosynthesis lib- erates free oxygen came in 1772, from the work of Priestley. Priestley showed that a mouse under a sealed bell jar can continue breathing more or less indefinitely, provided that a green plant is also placed under the jar. Within another ten years, Ingenhousz, a Dutch physician, had shown that light must be available if this experiment is to work, and that only the green part
. Principles of modern biology. Biology. Nutrition of Green Plant Cells - 159 mediary stages. Nevertheless it was many years before even this much information be- came available. The first inkling that photosynthesis lib- erates free oxygen came in 1772, from the work of Priestley. Priestley showed that a mouse under a sealed bell jar can continue breathing more or less indefinitely, provided that a green plant is also placed under the jar. Within another ten years, Ingenhousz, a Dutch physician, had shown that light must be available if this experiment is to work, and that only the green parts of a plant are effective. In 1804 de Saussure found that the weight gained by a plant growing in a sealed atmosphere was distinctly greater than the weight of the carbon dioxide lost by the at- mosphere. Thus de Saussure concluded that water (as well as carbon dioxide) must be an essential ingredient in the photosynthetic re- action. During the rest of the nineteenth century, the quantitative aspects of the over- all reaction were established by the work of many investigators. Chlorophyll and Chloroplasts. One of the most essential enzymes in photosynthesis is a chlorophyll-protein complex, which is often referred to, rather loosely, as chloro- phyll. The nonprotein part, chlorophyll proper, which can be extracted from leaves by ether and similar solvents, proves to be a green pigment with a rather compli- cated molecular structure (Fig. 9-1). Struc- turally, the chlorophyll-protein complex tends to resemble hemoglobin, the red pro- tein pigment of blood, except that a magne- sium, rather than an iron, atom occupies a central position in the pigment part of the molecule; and attached peripherally there is a long-chain alcohol, phytol. In addition to chlorophyll, the cells of higher plants con- tain two other pigments: the deep orange xanthophyll (p. 596) and the bright yellow carotene (p. 350); and the cells of blue-green and red algae (p. 600) possess the accessory pigments
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