Biology · Class 12 Science

Ch 1Sexual Reproduction in Flowering Plants — Class 12 Biology, concept-first.

Sexual reproduction is what makes flowering plants worth admiring the way we do — every flower's scent, colour, and shape exists to serve that one purpose, not for our benefit.

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Key concepts

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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.

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Chapter contents

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Introduction

Sexual reproduction is what makes flowering plants worth admiring the way we do — every flower's scent, colour, and shape exists to serve that one purpose, not for our benefit.

1.1

Flower – A Fascinating Organ of Angiosperms

People have valued flowers for as long as human history goes back — not just biologically, but aesthetically, socially, religiously, and culturally.

1.2

Pre-Fertilisation: Structures and Events

Long before a flower is even visible on a plant, the decision to flower has already been made — hormonal and structural changes trigger the differentiation of the floral primordium, which develops int…

1.2.1

Stamen, Microsporangium and Pollen Grain

The stamen is the male reproductive unit of a flower. It consists of two parts: a long, slender stalk called the filament, and a terminal, generally bilobed structure called the anther.

1.2.2

The Pistil, Megasporangium (Ovule) and Embryo Sac

The pistil is the female reproductive unit of the flower. A flower may have a single pistil (monocarpellary) or multiple pistils (multicarpellary).

1.2.3

Pollination

Flowering plants produce male and female gametes — the pollen grain and the embryo sac, respectively. Neither of these gametes can move on its own.

1.3

Double Fertilisation

After the pollen tube enters one of the synergids, it releases its two male gametes into the synergid's cytoplasm.

1.4

Post-Fertilisation: Structures and Events

Once double fertilisation is complete, the zygote and the primary endosperm nucleus (PEN) begin the transformation of the ovule into a seed and the ovary into a fruit.

1.4.1

Endosperm

The endosperm is the nutritive tissue that supports the developing embryo. Its development actually begins before the embryo starts to form.

1.4.2

Embryo

The embryo develops at the micropylar end of the embryo sac, precisely where the zygote is located. Most zygotes do not divide immediately after fertilisation — they wait until a certain amount of end…

1.4.3

Seed

The seed is the final product of sexual reproduction in angiosperms. It is a fertilised ovule, and seeds are always formed inside fruits.

1.5

Apomixis and Polyembryony

Most flowering plants reproduce sexually — pollen meets ovule, double fertilisation happens, and a seed forms with a unique genetic mix. But nature has a few shortcuts.

Summary

- Structure of a flower: The male reproductive unit is the stamen (anther + filament); the female unit is the pistil/carpel (stigma, style, ovary).

Exercises

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Exemplar Problems

Higher-order thinking / exemplar-style practice problems.

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Sample & Board Papers

Sample papers and previous-year board questions for this subject.

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Q1(a) Describe any two devices in a flowering plant which prevent both autogamy and geitonogamy. (b) Explain the events upto double fertilisat…Preview