Food in a human...
What must cells be able to do?
...cells lining stomach release an enzyme to break down food molecules
...grab smaller molecules produced by digestion, move them inside
...release some of those molecules for other cells to use, too (e.g. muscles, brain)
...all cells re-configure those molecules to make human cell parts
There must be different cell types to do different functions, but they all have the same basic requirements.
Some essential cell types:
Digestive system to break down food
Transport system to move food molecules to other cells
Gas exchange system to deal with CO2 and O2
etc