. Biology and man. Biology; Human beings. HOW DIFFUSION TAKES PLACE If we throw balls of different sizes at a tennis net, we may expect most of the smaller balls to go through the net, and all or most of the larger ones to be stopped. In much the same way, we imagine, some of the rapidly moving molecules of dissolved substances pass through the pores of an osmotic membrane, while larger molecules move through in smaller numbers or not at all pens in roots and in other parts of living things if we think of this work as the action of the rapidly moving molecules. But there is still the problem o
. Biology and man. Biology; Human beings. HOW DIFFUSION TAKES PLACE If we throw balls of different sizes at a tennis net, we may expect most of the smaller balls to go through the net, and all or most of the larger ones to be stopped. In much the same way, we imagine, some of the rapidly moving molecules of dissolved substances pass through the pores of an osmotic membrane, while larger molecules move through in smaller numbers or not at all pens in roots and in other parts of living things if we think of this work as the action of the rapidly moving molecules. But there is still the problem of understanding how roots work, since they seem to be raising water against gravity, and they seem, at any rate, to be taking more out of the soil than they might be giving off. The cell walls of the root, and of practically all plant parts, consist of cellulose, a substance that does not dissolve in water, but does absorb water in the same way as glue or gelatin. Now, we must imagine that wherever there is water, substances dissolved in it will diffuse in it. When the cellulose walls of root-hair cells are saturated with water, the molecules of dissolved substances diffuse through this water. This kind of "diffusion through a membrane" is called osmosis, from a Greek word meaning "to push". We conceive osmosis to be taking place through the walls of all cells, those of animals as well as those of plants. Since the liquid or solution inside the root hair is different from the soil water surrounding the cell, we should expect that some of the substances would be diffusing into the cell, and other substances moving out of the cell. 86. 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 Gruenberg, Benjamin C. (Benjamin Charles), 1875-1965; Bingham, N. Eldred (Nelson Eldred), 1901-. Boston, New
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