# Why are cells so small?

In this video, I use diffusion cubes to show why cells are so small. A small cell with a large surface area to volume ratio can efficiently move materials into the cell.

Diffusion is a type of passive transport that cells use in order to move materials like oxygen and carbon dioxide into and out of the cell. The common phrase used with diffusion is " high to low is the only way to go." Objects will flow from an area of high concentration to an area of low concentration without the use of energy. Cells use diffusion and osmosis in order to move materials like oxygen and glucose into the cell.
A cell with a larger surface area to volume ratio is more efficient at moving material than a cell with a smaller ratio.

How do you calculate the surface area to volume ratio of a rectangle?
First, calculate the surface area of each side ( 6 total) and add these together.
Calculate the volume using length x width x height
Divide surface area by volume.

Here is my recipe for the diffusion blocks
gelatin
Ammonia
Phenolphthalein

The more gelatin you use the more rigid your diffusion blocks will be.

If you soak the diffusion cubes in vinegar then the phenolphthalein will turn pink when it comes in contact with the vinegar which allows you to see the rate of diffusion.
When the vinegar comes in contact with the ammonia a base is created and the Phenolphalein turn pink.
The diffusion cubes are a fun way to watch diffusion occur.

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