From among the situations given below, choose the one that prevents both autogamy and geitonogamy. (a) Monoeci

NCERT Exemplar · Q13

Q. From among the situations given below, choose the one that prevents both autogamy and geitonogamy.

(a) Monoecious plant bearing unisexual flowers

(b) Dioecious plant bearing only male or female flowers

(d) Dioecious plant with bisexual flowers

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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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A dioecious plant bearing only male or female flowers prevents both autogamy (self-pollination within the same flower) and geitonogamy (pollination between different flowers on the same plant) because each plant produces only one sex of flower, making self-pollination impossible.

To understand why, we need to first be clear about what autogamy and geitonogamy mean. Autogamy is self-pollination within the same flower — pollen lands on the stigma of the same flower. Geitonogamy is pollination between two different flowers on the same plant — pollen from one flower reaches the stigma of another flower on the same individual. Both are forms of self-pollination, and both are genetically equivalent to self-fertilisation because the pollen and ovule come from the same parent plant.

Now, consider each option.

A monoecious plant bearing unisexual flowers (option A) has separate male and female flowers on the same plant. This prevents autogamy because no single flower has both male and female parts. But geitonogamy is still possible — pollen from a male flower can easily reach the stigma of a female flower on the same plant. So this option fails to prevent both.

A monoecious plant with bisexual flowers (option C) has flowers that contain both stamens and carpels. Here, autogamy is possible — pollen from the same flower can land on its own stigma. Geitonogamy is also possible between different flowers on the same plant. So this option prevents neither.

A dioecious plant with bisexual flowers (option D) is a contradiction in terms. Dioecy means male and female flowers occur on separate plants. If a plant has bisexual flowers, it cannot be dioecious. This option is biologically impossible, so it is not a valid situation. …

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Q.From among the situations given below, choose the one that prevents both autogamy and geitonogamy.

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