1. Why are cells so small??

2. The Size Of Cells.
As cells increase in size, their volume increases more rapidly than their surface area.
Small cells have a large Surface area to volume ratio (large surface area relative to a small volume)

3. What Is The Advantage Of Having A Large SA:Volume ratio?
This means that more of the surface of the cell is in contact with it’s surroundings.
This allows for a greater rate of diffusion of gases and nutrients in and out of the cell

4. Prove It!
In a cube with sides of 1cm, each face has an area of 1cm x 1cm = 1cm2
Since the cube has 6 faces, the total surface area is 6cm2
The volume of the cube is 1x1x1=1cm3
The surface area:volume ratio is 6:1
S:A Volume

5. Prove It!
A cube with sides of 2cm will have a surface area of 2x2x6=24cm2
And a volume of 2x2x2=8cm3
The surface area to volume ratio 24:8 = 3:1
S.A. Volume

6. Conclusion
So as the cube increases in size, the SA:Volume ratio decreases.
Therefore as a cell increases in size, its ability to diffuse nutrients in and wastes out will decrease.
This is why cells are small