The generative cell of a two-celled pollen divides in the pollen tube but not in a three-celled pollen. Give r

NCERT Exemplar · Q47

Q. The generative cell of a two-celled pollen divides in the pollen tube but not in a three-celled pollen. Give reasons.

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Concept understanding — Male And Female Gametophyte

Let’s start with something you already know. Think of a plant like a mango tree. It produces flowers, and those flowers eventually turn into mangoes. How does that happen? The flower is the plant’s reproductive organ, and inside it, two tiny but crucial structures are made: the male gametophyte and the female gametophyte. These are not the “male” and “female” parts of the flower themselves (like the stamen and pistil) — they are the microscopic, single-generation cells that actually carry the genetic material to form the next plant.

The everyday intuition

Imagine you are baking a cake. The male gametophyte is like the packet of dry yeast — it’s small, mobile, and needs to be added to the mixture. The female gametophyte is like the bowl of flour, eggs, and sugar — it’s larger, stationary, and provides the environment where the yeast works. Without the yeast reaching the bowl, no cake rises. Without the bowl, the yeast has nothing to act on. In a flower, the male gametophyte (pollen grain) must travel to the female gametophyte (embryo sac) for fertilisation to happen.

The precise meaning

In NCERT biology, the male gametophyte is the pollen grain. It develops inside the anther (the top part of the stamen). A mature pollen grain contains two cells: a tube cell and a generative cell. The tube cell will grow a long tube down the style of the pistil, and the generative cell will divide to form two sperm cells. So the male gametophyte is not the whole stamen — it’s the tiny, single-celled (or two-celled) structure that carries the male genetic material.

The female gametophyte is the embryo sac. It develops inside the ovule, which is located in the ovary of the pistil. The embryo sac is a seven-celled, eight-nucleate structure (though you don’t need to memorise numbers for a prose subject — just know it’s a small, organised sac). It contains the egg cell (the female gamete) and other cells that help in fertilisation and nourishment. The female gametophyte is not the whole pistil — it’s the microscopic sac inside the ovule.

Important

The male gametophyte (pollen grain) is haploid — it has only one set of chromosomes. The female gametophyte (embryo sac) is also haploid. When they fuse during fertilisation, they form a diploid zygote, which grows into the seed. This is why both are called “gametophytes” — they produce gametes (sperm and egg).

Why it matters …

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The generative cell in two-celled pollen divides in the pollen tube because it is shed before this division occurs, while in three-celled pollen, the generative cell has already divided into two male gametes before shedding.

To understand why the generative cell behaves differently in two-celled versus three-celled pollen, we must first grasp the fundamental structure and purpose of a pollen grain. A pollen grain represents the male gametophyte in flowering plants. Its primary role is to deliver the male gametes to the ovule for fertilisation.

At maturity, a pollen grain typically contains two main cells:

Vegetative cell (or tube cell): This is a larger cell with abundant food reserves and an irregularly shaped nucleus. Its primary function is to form the pollen tube, which grows through the stigma and style to reach the ovule.
Generative cell: This is a smaller cell that floats in the cytoplasm of the vegetative cell. Its role is to divide and produce the male gametes.

The difference between two-celled and three-celled pollen lies in the developmental stage at which the pollen grain is shed from the anther.

Two-Celled Pollen

In approximately 60% of angiosperms, pollen grains are shed at a "two-celled stage." This means that when the pollen is released from the anther, it contains:

One large vegetative cell.
One smaller generative cell.

Upon landing on a compatible stigma, the pollen grain absorbs moisture and nutrients, causing the vegetative cell to enlarge and emerge as a pollen tube. As the pollen tube grows through the stigma and style, the generative cell, which is carried along within the pollen tube, undergoes a mitotic division. This division produces two non-motile male gametes. These two male gametes are then delivered to the embryo sac for the process of double fertilisation.

Note

The division of the generative cell into two male gametes is a mitotic division, ensuring that the genetic material of the gametes is identical to that of the generative cell.

Three-Celled Pollen

In the remaining 40% of angiosperms, pollen grains are shed at a "three-celled stage." In these plants, the generative cell divides mitotically to form two male gametes before the pollen grain is shed from the anther. Therefore, when this type of pollen is released, it already contains:

One large vegetative cell.
Two male gametes. …

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Q.The generative cell of a two-celled pollen divides in the pollen tube but not in a three-celled pollen. Give reasons.

Two-Celled Pollen

Three-Celled Pollen

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