The quality of the cells depends on the ability of the individual cells to activate the different cell sections that are responsible for certain functions.  For example, changes in the cell surface, the metabolic flow and signal transmission within the individual cell are prerequisites for the sperm to recognise an egg cell, penetrate it and ultimately cause it to fuse. New studies also indicate that some of these functions paradoxically only serve to block the penetration of other sperm into the egg cell found. All of these known mechanisms make it understandable, which is why only the examination of these sperm functions allows a true assessment of the fertilization ability of a sperm cell or an ejaculate.