Question

If an egg cell were treated with EDTA, a chemical that binds calcium and magnesium ions,

(A) the acrosomal reaction would be blocked.

(B) the fusion of sperm and egg nuclei would be blocked.

(C) the fast block to polyspermy would not occur.

(D) the fertilization envelope would not form.

Short answer

(A)The option “the acrosomal reaction would be blocked” is incorrect.

(B)The option “the fusion of sperm and egg nuclei would be blocked” is incorrect.

(C)The option “the fast block to polyspermy would not occur” is incorrect.

(D)The option “the fertilization envelope would not form” is correct.

Step-by-step solution

Role of calcium and magnesium in the egg cell.

Calcium is a macro element since it is a necessary component for developing good-quality eggshells in eggs. They, like other nutrients, must be ingested in sufficient amounts and as part of a well-balanced diet.

Explanation of option ‘(A)’

The acrosomal reaction occurs after capacitation of the sperm, caused by a Ca++ influx. This process is important for fertilization as it helps the sperm enter the zona of the egg. The absence of Ca++ influx can block this process.

Thus, the acrosomal reaction will not be blocked by the reaction of EDTA with the egg cell.

Therefore, the given option is incorrect.

Explanation of option ‘(B)’

The process of fertilization occurs when the sperm fuses the egg nucleus. The sperm fuses the corona radiata and enters the egg nucleus. The fusion causes the release of Ca2+ signal from the egg that blocks other sperms to bind the egg.

Thus, the fusion of sperm and egg will not be blocked by the reaction of EDTA with the egg.

Therefore, the given option is incorrect.

Explanation of option ‘(C)’

The fast block to polyspermy is activated when the egg changes its electric potential. The ionic concentration of the egg changes and is different from the external environment. The fast block occurs when one sperm has already fused the egg.

Thus, the fast block to polyspermy can occur if treated with EDTA.

Therefore, the given option is incorrect.

Explanation of option ‘(D)’

If the fertilizing egg cell is treated with EDTA, the fertilization envelope will not form. The cortical granules bring in heavy carbohydrates and water to build a tight fertilization sheath around the egg.

Thus, if treated with EDTA, the fertilization envelope does not form.

Therefore, the given option is correct.