Re: Why is it necessary for cells to be small?

You're right!!! Cells are quite small, so small that we can't see them with the naked eye. Here is a picture from a tutorial on cells at the University of Arizona that compares the size of different kinds of cells to other items:

Cells are constrained in their size because they have to exchange materials with the environment. These materials include water, gases, and nutrients. Cells pass these materials through their outer surface.

An object has a limited surface area. The diagram below shows how the ratio of surface area to volume decreases as an object becomes smaller. That is, the smaller an object, the more surface area it has in relationship to its volume.

You can understand this a bit better when you think about dissolving something in water. For instance, a sugar cube dissolves more slowly than regular sugar, and regular sugar dissolves more slowly than powdered sugar. The sugar cube has less surface area for its volume, and it takes more time to dissolve.

Animal and plant cells are bigger than bacteria because they have more sophisticated systems for transporting nutrients from the surface. This is described in detail at this site at Hillfield-Strathallan College.

It is also convenient for cells to be small, because having small cells allows multicellular organisms (like you) to tolerate some cell death. Imagine if your arm were one cell...what would happen if it was injured? When you get a wound or burn, some cells are damaged and die, but other cells around them can multiply (to a limited extent) and replace those that died. It wouldn't work well for you to lose an arm when you accidentally touched a hot burner!