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

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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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