Biology - Human Reproduction Question with Solution | TestHub
Which of the following cells is NOT enclosed by zona pellucida?
Options:
Answer:
Solution:
According to the NCERT, during oogenesis, the tertiary follicle changes into the mature Graafian follicle. At this stage, the secondary oocyte forms a new non-cellular membrane called the zona pellucida around it.
The primary oocyte is present in the earlier stages of follicular development (primordial, primary, secondary, and early tertiary follicles) and is not enclosed by the zona pellucida.
The first polar body is formed after the completion of meiosis I and is extruded into the perivitelline space, which is the space between the plasma membrane of the secondary oocyte and the zona pellucida. Thus, it is enclosed by the zona pellucida.
The true ovum is formed after the secondary oocyte completes meiosis II upon fertilization. The zona pellucida remains intact around the ovum and the developing embryo until the blastocyst stage (when hatching occurs) to prevent polyspermy and ectopic implantation.
Therefore, the primary oocyte is the only cell among the given options that is not enclosed by the zona pellucida.
Answer: Primary oocyte
