What do organisms have based on their functions?

Unicellular organisms, cells perform all the basic actions and functions required for living like nutrition, respiration, reproduction etc.

In multicellular organisms, cells divide their tasks on the basis of "DIVISION OF LABOUR" to specialize in certain functions besides respiration etc. Like conduction in neurons, excitation in muscles, RBC production by bone marrow etc.

The problem here is that according to aufbau principle before 3d orbital 4s subshell comes.after filling 3p orbital with electrons you have 4 electrons left, you place two in 4s with opposite spin and the other two in 3d in any of its two orbitals of total five orbitals with the same spin.