Question

Arrange the formation of the following cells in the ovary in the sequential order:
i) Ovum
ii) Primary follicle
iii) Primary oocytes
iv) Graafian follicle

• A. ii), i), iv), iii)
• B. iii), ii), i), iv)
• C. iii), ii), iv), i)
• D. i), ii), iii), iv)

Answer 1

Answer: (C)

In an ovary, there are millions of oocytes. An oocyte is not the same thing as a germ cell. The germ cells develop in the fetal ovary and before birth begin meiosis, and then freeze right at the start of the first meiotic division. These cells are stopped in prophase I of meiosis I, and are called primary oocytes. They lie within the ovaries surrounded by other cells, the follicular cells. The primary oocyte plus its follicular cells comprise the primary follicle.
At puberty, each oocyte enters meiosis again, just before it is ready to be ovulated. This means some oocytes can remain dormant for up to 50 years. FSH and LH act on a primary follicle in the ovaries, promoting its development into a secondary follicle.
The secondary follicle will continue to develop, and eventually forms a mature ovarian follicle called a tertiary, or Graafian, follicle. Once this mature follicle has developed, the further rise in oestrogen leads to a surge in LH (and some FSH), which stimulates ovulation.
The ovum (surrounded by its zona pellucida and cumulus of granulosa cells) will burst out of the follicle, ovulated and free to travel towards the uterus, hoping to meet a sperm cell on the way.