Final answer:
The apical surface is found on top of the cells, while the basal surface is found underneath. Epithelial cells have different structures and functions on these surfaces.
Step-by-step explanation:
The surface that is found on top of the cells is called the apical surface, while the surface found underneath is called the basal surface.
Epithelial cells, which cover the surfaces of organs and tissues, have a distinct polarity, with different structures and functions on the apical and basal surfaces. The apical surface is involved in functions such as absorption and secretion, while the basal surface is responsible for anchoring the cells to the underlying tissue.
For example, in the skin, the apical surface of the epidermal cells is exposed to the external environment, while the basal surface is attached to the underlying connective tissue through the basal lamina and the reticular lamina, forming a basement membrane.