Thermodynamics and Cell Shapes

Why are protoplasts (cells devoid of cell wall) spherical? Why are most of the unicellular organisms (prokaryotes and eukaryotes) spherical? A sphere is a form which provides maximum surface area for absorption and interaction. In this form a cell remains at the lowest possible energy. In tissues, cells acquire different fops like polygonal, rectangular, irregular etc. Here the concern is to accommodate maximum number of cells in minimum area, so that complete functions are being taken care of.