Question

Choose the incorrect statement from the following.

• A. In birds and mammals internal fertilisation takes place
• B. Colostrum contains antibodies and nutrients
• C. Polyspermy in mammals is prevented by the chemical changes in the egg surface
• D. In the human female, implantation occurs almost seven days after fertilisation

Answer 1

Answer: (C)

Internal fertilization is a type of fertilization in which there is union of an egg and sperm inside the body of a parent. Examples include reptiles, mammals, birds. Colostrum is the first form of milk that is produced by the mammary glands of mammals. It contains large numbers of $IgA$ antibodies and lymphocytes that help protect the mucous membranes of the infant. Polyspermy is a condition in which egg has been fertilized by more than one sperm. It is prevented by depolarization of the egg plasma membrane after the entry of first sperm. This depolarization prevents the entry of additional sperms. The fertilized ovum enters the uterine cavity $3-4$ days later. Implantation occurs almost $7$ to $10$ days after fertilization and $5$ to $6$ days after it has entered the uterine cavity.
Thus, the correct answer is 'Polyspermy is prevented by the chemical changes on the egg surface..'