Final answer:
A secondary oocyte becomes an ovum only after fertilization, when it completes meiosis II by releasing the second polar body and fuses with sperm to form a zygote. If fertilization does not take place, it disintegrates without becoming an ovum.
Step-by-step explanation:
Is a Secondary Oocyte an Ovum?
During the process of oogenesis, the transition from a primary oocyte to a secondary oocyte occurs as a result of hormonal triggers, specifically a surge of luteinizing hormone just prior to ovulation. At this point, the primary oocyte completes meiosis I, yielding a haploid secondary oocyte and a smaller polar body which typically disintegrates. It is essential to note that a secondary oocyte is not yet an ovum. The secondary oocyte, once released from the ovary during ovulation, will begin meiosis II but arrests at the metaphase II stage. It remains in this state unless fertilization occurs.
Fertilization is the critical event that prompts the completion of meiosis II in the secondary oocyte, resulting in the formation of a second polar body and a haploid ovum (ootid), which then combines with the haploid sperm to form a zygote with a full set of chromosomes. Hence, it is only after the release of the second polar body, following sperm entry, that the secondary oocyte can be rightfully termed an ovum. If fertilization does not occur, the secondary oocyte disintegrates, never having become a mature ovum.