Biconcave discs appear in the study of cell biology, as an approximation to the shape of certain cells, including red blood cells.
Mathematical model
A biconcave disc can be described mathematically by
where z(r) is the height of the surface as a function of radius r, D is the diameter of the disc, and a0, a1, a2 are coefficients describing the shape. The above model describes a smooth surface; actual cells can be much more irregular.
Biology
Erythrocytes (also known as Red Blood Cells) are in the shape of a biconcave disc. An erythrocyte is also known as a red blood cell and transports oxygen to and from tissues.[1][2]