. Animal growth and development. Embryology; Growth; Biology; Growth; Embryology; Animals -- growth & development. 94 Growth and Form Other cells cannot convert N2 to NH3, but if given NH3 and pyruvic acid they can make alanine. Still other cells, which do not possess any of the enzymes that catalyze these reactions, must be supplied with alanine itself if they are to grow. The diversity of nutritional requirements results from the inability of cells to synthesize one or another protoplasmic constitu- ent. The S-Shaped Curve of Growth Figure 44 shows growth curves which, as you can see, ar
. Animal growth and development. Embryology; Growth; Biology; Growth; Embryology; Animals -- growth & development. 94 Growth and Form Other cells cannot convert N2 to NH3, but if given NH3 and pyruvic acid they can make alanine. Still other cells, which do not possess any of the enzymes that catalyze these reactions, must be supplied with alanine itself if they are to grow. The diversity of nutritional requirements results from the inability of cells to synthesize one or another protoplasmic constitu- ent. The S-Shaped Curve of Growth Figure 44 shows growth curves which, as you can see, are S-shaped. The abscissa is time—minutes, days, hours, years, depending on the organ- ism studied. The ordinate is growth and can describe the number of cells in a bacterial culture, the number of human beings on earth, the size or weight of a sunflower seedling or a rat, the size or weight of the heart or the brain. In other words, the ordinate is a measure of the growth of a population or a single organism or any of its parts and, when growing under optimal conditions, all show precisely this sort of growth curve. Many questions come to mind when we look at this curve. Why does growth start? Why does it stop? Why is the curve S-shaped? In this discussion of the factors affecting growth, we shall deal with Fig. 44a. The growth curve of the human population of the world. The circles indicate census totals, the solid line the mathematically fitted, smooth, S-shaped curve (after Pearl and Gould, from Allee, et Prin- ciples of Animal Ecology).. 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 Sussman, Maurice. Englewood Cliffs, N. J. , Prentice-Hall
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