. Embryology. Embryology; Embryology; genealogy. ENERGY SOURCES 253 Energy sources What is the energy source for the synthesis of raw materials into proto- plasm ? What substances are oxidized to carbon dioxide and water to provide the energy for the synthesis of the large molecules in a growing cell ? In the amphibian egg the amount of carbohydrate in the egg begins to decrease sharply at about the time of gastrulation (Fig. 165). This carbohydrate breakdown may furnish the energy for early development, just as carbohy- drate breakdown in a muscle furnishes the energy for muscular contraction
. Embryology. Embryology; Embryology; genealogy. ENERGY SOURCES 253 Energy sources What is the energy source for the synthesis of raw materials into proto- plasm ? What substances are oxidized to carbon dioxide and water to provide the energy for the synthesis of the large molecules in a growing cell ? In the amphibian egg the amount of carbohydrate in the egg begins to decrease sharply at about the time of gastrulation (Fig. 165). This carbohydrate breakdown may furnish the energy for early development, just as carbohy- drate breakdown in a muscle furnishes the energy for muscular contraction. As a matter of fact, the same types of enzymes which play a part in the break- down of carbohydrates in muscle are also present in the frog egg. Now the energy derived from the breakdown of carbohydrates may be used for several purposes. It is needed, first of all, for the synthesis of the protoplasm in the egg. Energy may also be necessary for the cell movements which take place during gastrulation. It is probably also used in the process of differentiation, because that process involves the formation of new com- pounds, presumably proteins. And finally, energy is also necessary for the maintenance of the embryo in a living condition. An embryo, like an adult, is constantly expending energy to keep its cells in the living condition. Carbohydrate breakdown is not the only source of energy. At about the time of hatching in the amphibian egg the lipids begin to be oxidized. If we analyze for the amount of fat in the egg we find that it stays fairly constant until just before hatching and then begins to be used up (Fig. 165). CASTRULATIO. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Barth, Lester G. (Lester George), 1905-1979. New York, Dryden Press
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