# BIOL1006 Lecture Notes - Lecture 12: Cell Membrane, Prokaryote

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9 Aug 2016
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Lecture 12
Small size, in general, is necessary for all cells, whether
prokaryotic or eukaryotic.
First, we'll consider the area and volume of a typical cell.
Not all cells are spherical in shape, but most tend to
approximate a sphere.
You may remember from your high school geometry
course that the formula for the surface area of a sphere
is 4πr2, while the formula for its volume is 4/3πr3.
Thus, as the radius of a cell increases, its surface area
increases as the square of its radius, but its volume
increases as the cube of its radius.
As a cell increases in size, its surface area-to-volume
ratio decreases.
This same principle would apply if the cell had the shape
of a cube.
If the cell grows too large, the plasma membrane will not
have sufficient surface area to support the rate of
diffusion required for the increased volume.
In other words, as a cell grows, it becomes less efficient.
One way to become more efficient is to divide; another
way is to develop organelles that perform specific tasks.
These adaptations led to the development of more
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