Ans. Fertilization in humans occurs when a sperm cell penetrates and fuses with an egg cell. This typically happens in the fallopian tubes. The sperm cell, which is motile, travels through the female reproductive tract and reaches the egg cell. The sperm then releases enzymes that help it penetrate the protective layers surrounding the egg. Once the sperm enters the egg, the nuclei of the sperm and egg fuse together, combining their genetic information to form a zygote.