MOVEMENTS OF MATERIALS INTO AND OUT OF THE CELL 59 



to pass into the blood which carries it all over the body. When this 

 blood, rich in dissolved food, reaches the cells of your finger there is 

 again an unequal distribution of molecules of digested food — within 

 the cells of your finger there is less food than in the blood. Hence, 

 diffusion again causes the movement from an area of greater concen- 

 tration to an area of lesser concentration which is within the cell. 

 Within the cell, diffusion continues and distributes the food to all parts 

 of the protoplasm. In case there are adjoining cells which are not in 

 contact with the blood, the food will continue to diffuse from cell to 

 cell until the concentration is equalized in all. 



Once within the cell the various amino acids may again be recon- 

 structed into proteins which form an integral part of your protoplasm. 

 The simple sugar may be changed into the more complex glycogen for 

 storage. Fatty compounds may be formed from the fatty acids and 

 glycerol which diffuses through the membrane. Thus, the protoplasm 

 is constructed — first food materials are broken down to a size small 

 enough to diffuse through the cell membranes, and then these small 

 particles may be reconstructed into more complex compounds within 

 the cell. It is through enzymes that these various changes are accom- 

 plished. We produce enzymes in our digestive organs which break the 

 food down, and there are enzymes within the cells of our bodies that 

 cause reconstruction of these products of digestion. 



When waste products are generated within a cell, they must be in 

 a soluble form which can pass out through the cell membrane. Carbon 

 dioxide, which is produced when food is used within the cell with an 

 energy release, accumulates so that there is more of this compound 

 within the cell than there is in the surrounding blood. Hence, it will 

 diffuse into the blood, but when this blood reaches the lungs it is richer 

 in carbon dioxide than the air in the lungs and we have a diffusion from 

 a liquid into a gas. When proteins are used for energy there will be 

 certain nitrogen-containing wastes that also accumulate in the cell. By 

 diffusion these pass out into the blood and are removed from the blood 

 by the kidneys. 



Now what about the movement of water into and out of cells through 

 osmosis? If we place some red blood cells in plain water, they will be- 

 gin swelling and in a short time will burst from the internal pressure. 

 The protoplasm of the cells contains substances in solution, but plain 

 water has none. Hence, through osmosis water begins moving into the 

 cell and the cell begins to swell until the outer membrane gets so tight 

 that it bursts. If we place red blood cells in water with 0.87 per cent 

 salt dissolved in it, they will remain normal — the passage of water into 

 and out of the cell will be equal because the dissolved minerals within 



