Choose the correct statement from the following: (a) Cleistogamous flowers always exhibit autogamy (b) Chasmogamous flowers always exhibit geitonogamy (c) Cleistogamous flowers exhibit both autogamy and geitonogamy (d) Chasmogamous flowers never exhibit autogamy

Choose the correct statement from the following: (a) Cleistogamous flowers always exhibit autogamy (b) Chasmog

NCERT Exemplar · Q11

Q. Choose the correct statement from the following:

(a) Cleistogamous flowers always exhibit autogamy

(b) Chasmogamous flowers always exhibit geitonogamy

(d) Chasmogamous flowers never exhibit autogamy

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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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Cleistogamous flowers, which never open, are obligatorily self-pollinating within the same flower, a process known as autogamy.

Flowering plants have evolved diverse strategies to ensure successful pollination, the transfer of pollen grains from the anther to the stigma. These strategies often involve adaptations in flower structure and timing, leading to different types of pollination mechanisms. Broadly, pollination can be categorized into self-pollination (autogamy and geitonogamy) and cross-pollination (xenogamy). The structure of the flower itself plays a crucial role in determining which of these mechanisms are possible or even guaranteed.

Two distinct types of flowers based on their opening mechanism are chasmogamous and cleistogamous flowers. Understanding their characteristics is key to discerning their pollination patterns.

Chasmogamous Flowers

These are the more common type of flowers that open and expose their anthers and stigma to the environment. Because they are open, chasmogamous flowers offer opportunities for various forms of pollination:

Autogamy (Self-pollination within the same flower): If the anthers and stigma of a chasmogamous flower mature at the same time and are positioned in a way that allows pollen from the anther to fall onto the stigma of the same flower, autogamy can occur.
Geitonogamy (Pollination between different flowers on the same plant): Pollen from the anther of one chasmogamous flower can be transferred to the stigma of another flower on the same plant. This is genetically similar to autogamy but ecologically requires a pollinating agent (like wind or insects).
Xenogamy (Cross-pollination between different plants): Pollen from a chasmogamous flower on one plant can be transferred to the stigma of a flower on a different plant of the same species. This is true cross-pollination, leading to genetic variation.

Note

Chasmogamous flowers, by being open, are exposed to external factors like pollinators and wind, making their pollination outcomes more variable. They can facilitate self-pollination or cross-pollination depending on the plant's specific adaptations and the presence of pollinators.

Cleistogamous Flowers

In contrast to chasmogamous flowers, cleistogamous flowers are unique because they do not open at all. They remain closed throughout their development. Within these closed flowers, the anthers and stigma are located very close to each other.

When the anthers dehisce (release pollen) inside the closed flower bud, the pollen grains invariably fall directly onto the stigma of the same flower.
This mechanism ensures that only self-pollination occurs. There is no possibility for pollen from another flower (even on the same plant) to reach the stigma, nor can pollen from a cleistogamous flower be transferred to another flower.

Important

Cleistogamous flowers are obligately autogamous. This means they always exhibit autogamy, guaranteeing seed set even in the absence of pollinators. This is an evolutionary adaptation to ensure reproduction under conditions where pollinators might be scarce or unreliable. Examples of plants exhibiting both chasmogamous and cleistogamous flowers include Viola (common pansy), Oxalis, and Commelina.

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