Why are cells so small?

Cells are small in order to get pass barriers. In particular, it has a small surface area to volume racio, which in turn allows it to carry more materials.

Explanation:

If cells are way to massive, it will require much more more energy to move the cell, the cell would not be able to remove all of its waste, and it would not get enough nutrients to survive

Even under favorable conditions, each bacterial species will have its own doubling time. For example, aerobic bacteria generally grow very fast and may have a doubling time of 30 minutes or less. 

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