. Principles of modern biology. Biology. The route from the 3-carbon PGA to the 5- carbon ribulose phosphate is very indirect, however. It involves the formation of a num- ber of interesting intermediaries, including 4-carbon (tetrose) and 7-carbon (heptose) sugars, as combinations and recombinations occur in the metabolic vortex. It is a cycle in the sense that the same intermediaries keep appearing over and over again. But only part of the PGA is cycled back to replenish the supplies of ribulose diphosphate. The rest goes into the building of glucose, amino acids, and other molecules essenti
. Principles of modern biology. Biology. The route from the 3-carbon PGA to the 5- carbon ribulose phosphate is very indirect, however. It involves the formation of a num- ber of interesting intermediaries, including 4-carbon (tetrose) and 7-carbon (heptose) sugars, as combinations and recombinations occur in the metabolic vortex. It is a cycle in the sense that the same intermediaries keep appearing over and over again. But only part of the PGA is cycled back to replenish the supplies of ribulose diphosphate. The rest goes into the building of glucose, amino acids, and other molecules essential to the life of the cell—as is shown in Figure 9-6. As will be explained later (p. 181), a few bacteria can synthesize glucose from COo and HL,0 at the expense of energy, derived not from light, but from the oxidation of certain inorganic compounds. This process of chemo- synthesis is of very limited occurrence, how- ever. Almost all organic matter, which sup- ports the life of this planet, comes into being as a result of the photosynthetic powers of the green plants. Considerably more than a billion tons a day of assorted carbohydrates, proteins, lipids, and other organic com- Nutrition of Green Plant Cells - 167 pounds are produced by green plants, al- though about 90 percent of this huge pro- duction comes from primitive, mainly uni- cellular algae in the sea. OTHER ASPECTS OF PLANT NUTRITION Nutrition among green plants is much sim- plified by the fact that a plant does not need to take in any preformed organic foods. All the foods are simple crystalloidal substances, present practically everywhere, and conse- quently they can be absorbed directly from the environment. Thus plants generally do not possess any digestive system, and the holophytic mode of nutrition does not in- clude any processes ingestion, digestion, and egestion. Accordingly, nutrition in typical plants begins with the process of absorption. Absorption in Unicellular and Colonial Plants. Virtually all
Size: 1566px × 1595px
Photo credit: © The Book Worm / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookcollectionbiodiversity, booksubjectbiology
