Question

Name the parts marked as 'A' and 'B' in the given diagram. Write in detail the changes that take place in a flower when the product of 'B' reaches 'A' till a fruit is formed.

Answer 1

Flower Structure

• Part A: Stigma – The stigma is the receptive tip of the pistil, where pollen grains are received.
• Part B: Anther – The anther is the part of the stamen responsible for producing and releasing pollen grains.

Anther Product:

The anther (B) produces pollen grains, which are the male reproductive cells in plants.

From Pollination to Fruit

1. Pollination

Pollination is the transfer of pollen grains from the anther (B) to the stigma (A).

2. Pollen Germination

Upon reaching the stigma, a pollen grain absorbs nutrients and begins to germinate, forming a pollen tube.

3. Pollen Tube Growth

The pollen tube grows through the style and reaches the ovule in the ovary, allowing male gametes to travel.

4. Fertilization

• One male gamete fuses with the egg cell → Zygote (syngamy)
• Another male gamete fuses with polar nuclei → Primary Endosperm Nucleus
• This is known as double fertilization (unique to angiosperms)

5. Post-Fertilization Changes

• Zygote → Embryo: The zygote undergoes mitosis, developing into an embryo
• Ovule → Seed: The ovule matures into a seed, developing a protective seed coat
• Ovary → Fruit: The ovary wall enlarges to form the fruit (pericarp)
• Other floral parts: Sepals, petals, stamens, and style typically wither and detach

Flower Anatomy Summary

• A – Stigma: Receives pollen grains
• B – Anther: Site of pollen grain production (microsporangium)

Post-Pollination Events

• Pollen-stigma interaction and recognition
• Pollen tube growth through the style
• Double fertilization:
  • Zygote formation (2n)
  • Endosperm formation (3n)
• Embryo development and fruit maturation