Surface area to volume ratio
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surface area to volume ratio limits cell size organelles are needed for specific cellular functions.
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In this topic, you will learn that: ✚
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Cells can be many different shapes and sizes, but very few are large enough to be seen by the human eye without the aid of a microscope. For cells to stay alive, their cytoplasm must exchange nutrients and waste with the external environment. This exchange occurs across the plasma membrane. Prokaryotic cells are much smaller than eukaryotic cells because they do not contain specialised organelles for specific tasks. Eukaryotic cells have compartmentalised organelles with specific roles so that the cell can carry out cellular processes efficiently.
FIGURE 1 The irregular shape of this unicellular organism (called a desmid) maximises the surface area to volume ratio.
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Surface area and volume
Biologists compare the surface area to volume ratio (SA:V) of cells when they compare cell size. Surface area refers to the surface area of the plasma membrane, the area surrounding the cell that is exposed to the external environment. Volume refers to the space taken up by the internal contents or cytoplasm. As a cell grows, both the surface area and the volume of the cell increase; however, the cell volume increases more than the surface area. This means that the bigger the cell, the more difficult it is for the cell to exchange nutrients and waste between the centre of the cell and the external environment. Small cells have a larger surface area to volume ratio than large cells. As a result, small cells are better at taking in nutrients and removing waste than large cells. The surface area to volume ratio limits how big a cell can grow.
surface area
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the total area of the plasma membrane that diffusion occurs across
volume
the total amount of space in a contained area
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BIOLOGY FOR VCE UNITS 1 & 2
OXFORD UNIVERSITY PRESS
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