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

Naming the Parts

• Part A: Stigma – the receptive tip of the pistil that receives pollen grains.
• Part B: Anther – part of the stamen that produces and releases pollen grains.

Product of B:

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

Changes from Pollination to Fruit Formation

1. Pollination

Transfer of pollen grains from the anther (B) to the stigma (A).

2. Pollen Germination

On reaching the stigma, the pollen grain absorbs nutrients and begins to germinate by producing a pollen tube.

3. Growth of Pollen Tube

The pollen tube grows through the style and reaches the ovule in the ovary. Male gametes travel through the tube.

4. Fertilization

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

5. Post-Fertilization Changes

• Zygote → Embryo: Zygote undergoes mitosis to become an embryo
• Ovule → Seed: The ovule matures into a seed with a protective seed coat
• Ovary → Fruit: The ovary wall enlarges and forms the fruit (pericarp)
• Other floral parts: Sepals, petals, stamens, and style generally wither and fall off

Summary of Flower Anatomy

• A – Stigma: Receptive surface for 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