A cell is the structural and functional unit of the body. Many cells together form the tissue. Many kinds of tissue together form an organ. Many organs together form a system. Many systems together form the human body. All human cells are diploid cells except the gametes, which are haploid cells. Largest human cell is ovum. Function of a cell is based on the kind of proteins present in it. Cell membrane and cytoplasm take up eosin and nucleus takes up hemetoxylin dye. Adipose cells appear pale, because lipid in the cell gets dissolved by xylene during the process of tissue preparation.