The gene that codes for the testis-determining factor (TDF) is found in or on the

A. Ca2+: prevents the entrance of any more sperm- While calcium ions play a role in the slow block to polyspermy, the fast block involves sodium ions.

B. Na+: prevents the entrance of more Na- The fast block to polyspermy involves sodium ions (Na+), but the depolarization of the egg membrane prevents the entrance of more sperm, not just more Na+.

C. Na+: prevents the entrance of Ca2+. The fast block prevents additional sperm from entering, not calcium ions.

D. Na+: prevents the entrance of any more sperm: The fast block to polyspermy involves the opening of sodium ion channels, leading to depolarization of the egg membrane. This depolarization prevents other sperm from binding to and penetrating the egg.

A. Penetrate the vagina: The acrosome does not play a role in penetrating the vagina. Its function is specifically related to the sperm's ability to penetrate the ovum, making this option incorrect.

B. Dissolve the stickiness of the semen: While enzymes do play a role in semen liquefaction, this is not the function of the acrosome. The acrosome is primarily involved in the process of fertilization, not semen modification.

C. Dissolve the mucosa of the uterus: The acrosome is not involved in dissolving the mucosa of the uterus. Its function is related to penetrating the barriers surrounding the ovum.

D. Penetrate barriers surrounding the ovum: The acrosome contains enzymes that break down the outer layers of the ovum (such as the zona pellucida), allowing the sperm to penetrate and fertilize the egg. This is the correct answer.