(a) Sectional view of human ovary:

(i) Primary follicle: It is a layer of granulosa cells which surrounds the primary oocyte.

(ii) Tertiary follicle: It is the transformed form of the secondary follicle which has a fluid-filled cavity called antrum.

(iii) Graafian follicle: It is the matured form of the tertiary follicle.

(iv) Corpus luteum: It is formed in the luteal phase during which the remaining parts of the Graafian follicle transform and form corpus luteum.

(b) Corpus luteum is responsible for the secretion of the hormone progesterone, which is essential for the maintenance of the endometrium.

OR

(a) Diagram of Pistil showing pollen tube growth in angiosperm:

(i) Stigma: It is located at the exposed end of the style, and it functions as the receptive surface for pollen grains.

(ii) Male gametes: It fuses with the egg nucleus to form the diploid zygote.

(iii) Micropyle: A small opening at the tip of integuments in flower.

(iv) Ovule: They are attached to a cushion-like structure called Placenta.

(b) Micropyle is a minute opening in the ovule of a seed plant through which the pollen tube usually enters. Seed absorbs water through the micropyle and makes it available for the germinating seed. It also helps in diffusion of respiratory gases for the growing embryo.