Neuron is the longest cell present in the human body. It is branched and elongated whereas, onion cells or cheek cells are too short in size as compared to neurons. Although if we consider the difference between cheek and onion cells then onion cells have cell wall whereas, cheek cells do not have a cell wall. Onion cells will be having large-sized vacuoles positioned in a center whereas, cheek cells have small-sized vacuoles in either side of cell.