Cells160-page2

Cells160-page2 - The overall limit to cell size seems to be...

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Cell - 2 Cell Organization and Cell Dimensions Most cells are very small – smaller than we can see with our unaided eye. While the benefits of a cellular organization seem fairly clear, we must look more closely at how a cell functions to understand why most cells are very small, and why multicellular organisms are comprised of many, many microscopic cells, rather than just a few enormous ones. Each cell needs to perform a number of functions while maintaining a pretty constant internal environment. Cells must exchange materials with the external environment, and undergo any number of chemical reactions, each with specific chemical requirements, in order to stay alive and do their jobs. The more things needed in a cell, the more exchanges have to occur through the membrane. If the volume of a cell becomes too large, there is not enough membrane surface area to accomplish all that needs to be done.
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Unformatted text preview: The overall limit to cell size seems to be this surface area/volume ratio. As the volume of a cell increases, the cell has proportionally less surface to exchange nutrients, gases and wastes with its environment to sustain the increasing volume. Within the cytoplasm, materials move by diffusion, a passive physical process that can work only for short distances. A large volume would inhibit the rate of movement too much for cells to function. However, cells with minimal metabolic needs can have larger volumes. Some exceptions are: The yolk of a bird is a single cell. Some nerve cells run from the spine to the toes of mammals (although the diameter is small and they are microscopic, maintaining a good surface area to volume ratio.) Some green algae, such as Caulerpa and Acetabularia (Kingdom, Protista) have huge cells, and often are multinucleate....
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