Question

a single cell can perform all the function then why do we need many cells?

Answer 1

many times our body is attacked by different viruses... which are many in number... which can damage our cell... so as many cells we have,, the probability of living safe life will be more.. as cell is fundamental basic unit of life..

Answer 2

I m not a biology student but remember there are many types of cell unicellular and multicellular bt our body has very complex structure as compared to unicellular organism like amoeba so one cell is not capable of maintaining body function and will die soon so many cells are required to do the same function.At last I want to say that our body complexity had made us multicellular