Question

Student to attempt either option (A) or (B): (A) What is meant by ‘right’ and ‘wrong’ type of pollen when pollen lands on the stigma? A two-celled right type pollen has landed on the stigma. Explain the events taking place till fertilization in angiosperms. Why is pollen pistil interaction said to be dynamic?
OR
(B)

• Give the schematic representation of oogenesis in human females indicating chromosome number at each step.
• In which part of the female reproductive system do the following events take place?
  
  • I. Formation of corpus luteum
  • II. Maturation of tertiary follicle
  • III. Fertilisation
  • IV. Implantation

Hint:

In angiosperms, double fertilization is a unique event. Oogenesis and reproductive processes are tightly regulated spatially in the female reproductive tract.

Answer 1

(A)

• ‘Right’ type of pollen is compatible with the stigma and initiates pollen germination; ‘wrong’ type is incompatible and does not germinate.
• After a compatible (right) pollen lands, it germinates to form a pollen tube through which male gametes travel.
• The tube grows through the style, enters the ovule via the micropyle, and releases two male gametes.
• One male gamete fuses with the egg (syngamy), the other with two polar nuclei (triple fusion), resulting in double fertilization.
• Pollen-pistil interaction is dynamic as the pistil selects suitable pollen and promotes or inhibits pollen tube growth accordingly.

OR
(B)

1. Oogenesis schematic:

• Oogonium (2n) → Primary oocyte (2n) → Secondary oocyte (n) + First polar body (n) → Ovum (n) + Second polar body (n)

1. Location of events:

• I. Corpus luteum – Ovary
• II. Tertiary follicle maturation – Ovary
• III. Fertilisation – Fallopian tube
• IV. Implantation – Uterus