## How does the amount of surfacearea affect the size of a cell

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### Re: How does the amount of surfacearea affect the size of a cell

It affects its ability to function.

Consider this: a sphere - let's pretend that it's a cell.

As the sphere (cell) grows its volume (inside) expands at a faster rate than its surface area (which is the shape of the sphere on the outside). Its continual growth makes diffusion inefficient and so things like food, oxygen, and wastes take much longer to leave the cell. Also, all of that volume would take up a larger amount of room in the body. Cells with small volume, and large surface area make for an efficient system without taking up more room than possible.

"...as a cell gets bigger there will come a time when its surface area is insufficient to meet the demands of the cell's volume and the cell stops growing." (http://staff.jccc.net/pdecell/cells/cellsize.html)

Now consider this: Flattening the sphere. This causes the surface area to increase faster than the volume. Why is this good? Because the more surface area allows for efficient diffusion: oxygen, food, water, and wastes can go through the cell at a faster rate allowing it to carry out its function at a faster rate, and at a workable size.

Consider this: a sphere - let's pretend that it's a cell.

As the sphere (cell) grows its volume (inside) expands at a faster rate than its surface area (which is the shape of the sphere on the outside). Its continual growth makes diffusion inefficient and so things like food, oxygen, and wastes take much longer to leave the cell. Also, all of that volume would take up a larger amount of room in the body. Cells with small volume, and large surface area make for an efficient system without taking up more room than possible.

"...as a cell gets bigger there will come a time when its surface area is insufficient to meet the demands of the cell's volume and the cell stops growing." (http://staff.jccc.net/pdecell/cells/cellsize.html)

Now consider this: Flattening the sphere. This causes the surface area to increase faster than the volume. Why is this good? Because the more surface area allows for efficient diffusion: oxygen, food, water, and wastes can go through the cell at a faster rate allowing it to carry out its function at a faster rate, and at a workable size.

- stereologist
- Garter
**Posts:**8**Joined:**Sat Dec 13, 2008 12:20 pm

### Surface area issues

Be careful here, surface area and volume are of different units. Observing which numbers are increasing faster or whatever is comparing apples and oranges.

You can also get yourself into trouble trying to do ratios.

It is best to fix one of the values and watch what happens when the other changes. For example, fix the volume and then see what different shapes offer for a surface area.

To see some confusion divide the volume of the sphere by the surface area of the sphere. The result is r/3. Now do the same for a cube remember to use 2s for the length of the edge so that we can compare 'radius' to 'radius' and not 'radius' to diameter.

(2s)^3/(6(2s^2)) = 2s/6 = s/3

This looks like the volume to surface area of spheres and cubes is the same. But spheres are supposed to have the best ratio.

What went wrong?

You can also get yourself into trouble trying to do ratios.

It is best to fix one of the values and watch what happens when the other changes. For example, fix the volume and then see what different shapes offer for a surface area.

To see some confusion divide the volume of the sphere by the surface area of the sphere. The result is r/3. Now do the same for a cube remember to use 2s for the length of the edge so that we can compare 'radius' to 'radius' and not 'radius' to diameter.

(2s)^3/(6(2s^2)) = 2s/6 = s/3

This looks like the volume to surface area of spheres and cubes is the same. But spheres are supposed to have the best ratio.

What went wrong?

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