Describe the process of oogenesis in humans. Draw a labelled sectional view of the ovary.
How to lay out the answer. Follow the frame, then write it in your own words.
1 · Define in one line. Oogenesis is the formation of a mature female gamete (ovum) in the ovary.
2 · Before birth. Oogonia form in the foetal ovary, enter prophase I and pause as primary oocytes; each is wrapped in granulosa cells as a primary follicle.
3 · Follicle growth after puberty. Primary follicle → secondary follicle (more granulosa layers and a theca) → tertiary follicle (antrum, theca interna and externa).
4 · Meiosis I and the Graafian follicle. The primary oocyte divides unequally into a secondary oocyte and a first polar body; the Graafian follicle forms and the zona pellucida appears.
5 · Ovulation and meiosis II. The Graafian follicle releases the secondary oocyte; meiosis II finishes only after sperm entry, giving the ovum and a second polar body.
6 · Draw the ovary. [Diagram: primary, secondary, tertiary and Graafian follicles, ovum, corpus luteum, blood vessels]
7 · Close in one line. So oogenesis gives one ovum per primary oocyte, unlike the four sperms from each primary spermatocyte.
Scoring tip: Mention the pause in prophase I and the unequal divisions. These two points separate a full-mark answer from an average one.
