Final answer:
A defect in the movement of human sperm towards the egg is likely due to a problem with the flagellum (A. Flagellum), which is the structure responsible for the motility of the sperm.
Step-by-step explanation:
If a human sperm is unable to move through the female body to reach the site of the egg, the sperm could have a defect in which of the following structures? The correct answer is A. Flagellum.
The structure responsible for the sperm's motility is the flagellum, commonly referred to as the tail. This flagellum is powered by ATP produced by tightly packed mitochondria located in the mid-piece of the sperm. Together, these allow the sperm to swim towards an egg in the female reproductive tract. A defect in the flagellum would mean the sperm cannot propel itself forward effectively, thereby making it unable to reach the egg.
Other structures such as the nucleus, which contains the haploid genetic material, the cell membrane, and the cytoplasm, are essential for other functions but are not the primary factors affecting the sperm’s ability to move.