Question

(i) Explain any four devices that flowering plants have developed to encourage cross-pollination. (ii) Why do plants discourage self-pollination?…

Accepted Answer

(a) (i) - Pollen release and stigma receptivity are not synchronized/ Either the pollen is released before the stigma becomes receptive or stigma becomes receptive much before the release of pollen. - Anther and the stigma are placed at different positions so that pollen cannot come in contact with the stigma of the same flower. - Self-incompatibility/genetic mechanism/prevention of self- pollen from fertilizing the ovules by inhibiting pollen germination or pollen tube growth in the pistil. - Production of unisexual flower. (ii) To prevent inbreeding depression/ to have more variations for better adaptation. OR (b) Menstrual cycle in a normal human female Phase Uterine event Ovarian event --- --- --- Proliferative phase/ Follicular phase Endometrium of the uterus regenerates through proliferation under the influence of estrogen follicles. Primary follicles in the ovary grow to become Graafian follicles under FSH. (Secretion of estrogens by the growing follicles). Luteal phase/ Secretory phase Maintenance of the endometrium (thickness) in the presence of progesterone. Ruptured Graafian follicle transforms into corpus luteum. (secretes large amounts of progesterone). Menstrual phase Breakdown of the endometrium lining of the uterus in the absences of progesterone from Corpus luteum. Primary follicles start maturing and developing in the ovary under the effect of FSH.

(a)
Explain any four devices that flowering plants have developed to encourage cross-pollination.
(ii)
Why do plants discourage self-pollination ? State any one reason.

Marking-scheme solution

More from Human Reproduction

Phase	Uterine event	Ovarian event
Proliferative phase/ Follicular phase	Endometrium of the uterus regenerates through proliferation under the influence of estrogen follicles.	Primary follicles in the ovary grow to become Graafian follicles under FSH. (Secretion of estrogens by the growing follicles).
Luteal phase/ Secretory phase	Maintenance of the endometrium (thickness) in the presence of progesterone.	Ruptured Graafian follicle transforms into corpus luteum. (secretes large amounts of progesterone).
Menstrual phase	Breakdown of the endometrium lining of the uterus in the absences of progesterone from Corpus luteum.	Primary follicles start maturing and developing in the ovary under the effect of FSH.