Class 12 Biology Chapter 1: Sexual Reproduction in Flowering Plants | Notes, Summary, Important Questions & PYQs | Toppers Hub

Class 12 Biology Chapter 1 Notes – Sexual Reproduction in Flowering Plants (New NCERT 2025-26)

Introduction

The ability to reproduce is one of the most fascinating characteristics of living organisms. In plants, flowering plants (angiosperms) reproduce sexually — a process that ensures variation and evolution.

Chapter 1 of the Class 12 Biology textbook (New NCERT 2025-26), titled “Sexual Reproduction in Flowering Plants,” introduces the structure, processes, and significance of reproduction in higher plants.

This chapter is very scoring in the CBSE Board exam, typically carrying 5–6 marks, and is also important for NEET Biology.

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Chapter Overview

Feature	Details
Chapter Name	Sexual Reproduction in Flowering Plants
Unit	Reproduction
Subject	Biology
Class	12 (CBSE / NCERT)
Weightage	5–6 marks
Main Topics	Flower structure, Pollination, Double Fertilization, Seed & Fruit formation

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1. Sexual Reproduction in Angiosperms

Flowering plants reproduce sexually through the formation of male and female gametes, pollination, fertilization, and development of seeds and fruits.
The flower is the reproductive unit where all sexual processes occur.

Key Functions of the Flower

• Stamen (Androecium): Male reproductive organ; produces pollen grains.
• Carpel (Gynoecium): Female reproductive organ; produces ovules.
• Petals & Sepals: Protect reproductive parts and attract pollinators.

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2. Structure of the Flower

A typical flower has four whorls arranged concentrically:

1. Calyx – Outer green sepals, protective.
2. Corolla – Colorful petals, attract pollinators.
3. Androecium – Stamens (male reproductive part).
4. Gynoecium – Carpels (female reproductive part).

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3. Pre-Fertilization Events

Pre-fertilization events include gametogenesis (formation of gametes) and pollination (transfer of pollen).

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A. Male Reproductive Part – The Stamen

Each stamen has:

• Anther: Bilobed, each with two microsporangia (total four).
• Filament: Supports the anther.

Inside the microsporangium, pollen grains are produced through microsporogenesis.

Microsporogenesis

• The microspore mother cell (MMC) divides meiotically to form four haploid microspores → pollen grains.
• Each pollen grain is two-celled:
• Vegetative cell (large, with nucleus and cytoplasm)
• Generative cell (divides later to form two male gametes)

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B. Female Reproductive Part – The Carpel (Pistil)

A carpel consists of:

• Stigma: Receives pollen.
• Style: Tube for pollen tube passage.
• Ovary: Contains one or more ovules.

Ovule Structure

• Each ovule has nucellus, integuments, and embryo sac.
• The embryo sac is the female gametophyte.

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Megasporogenesis

• The megaspore mother cell (MMC) in the ovule undergoes meiosis, producing four haploid megaspores.
• Out of these, three degenerate, and one functional megaspore forms the embryo sac.

Embryo Sac Structure

• Consists of seven cells and eight nuclei:
• Three antipodals (at chalazal end)
• Two synergids + one egg cell (at micropylar end)
• Two polar nuclei (in the center)

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4. Pollination

Pollination is the transfer of pollen grains from the anther to the stigma of a flower.

Types of Pollination

Type	Description	Example
Self-pollination (Autogamy)	Pollen from the same flower	Pea
Geitonogamy	Pollen from another flower on same plant	Maize
Cross-pollination (Xenogamy)	Pollen from different plant	Papaya

Agents of Pollination

1. Wind (Anemophily) – Grass, maize.
2. Water (Hydrophily) – Vallisneria.
3. Insects (Entomophily) – Rose, sunflower.
4. Animals/Birds (Zoophily) – Bats, birds.

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5. Double Fertilization (Unique to Angiosperms)

Discovered by Nawaschin (1898).

Process:

1. Pollen germination: Pollen lands on stigma → forms pollen tube.
2. Pollen tube carries two male gametes to the embryo sac.
3. First male gamete fuses with egg cell → forms zygote (syngamy).
4. Second male gamete fuses with two polar nuclei → forms triploid endosperm (triple fusion).

➡️ Syngamy + Triple Fusion = Double Fertilization
➡️ It is unique to flowering plants.

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6. Post-Fertilization Events

After double fertilization:

Structure	Develops Into
Zygote	Embryo
Triploid primary endosperm nucleus	Endosperm
Ovule	Seed
Ovary	Fruit

Seed Formation

• Monocot seeds: One cotyledon (Maize).
• Dicot seeds: Two cotyledons (Pea).

Fruit Formation

• After fertilization, ovary transforms into fruit and ovules into seeds.
• The outer wall of ovary becomes the pericarp (fruit wall).

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7. Apomixis and Polyembryony

Apomixis

Formation of seeds without fertilization.
Example: Citrus, Mango.

Polyembryony

Formation of more than one embryo in a single seed.
Example: Citrus.

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8. Summary Notes (Quick Revision)

• Flower = Reproductive organ of angiosperms.
• Microsporogenesis → formation of pollen grains.
• Megasporogenesis → formation of embryo sac.
• Pollination = Transfer of pollen from anther to stigma.
• Double fertilization = Syngamy + Triple fusion.
• Endosperm nourishes the embryo.
• Ovary → Fruit; Ovule → Seed.
• Apomixis & polyembryony → variations of sexual reproduction.

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Important Questions (CBSE & NEET Focus)

1 Mark Questions

1. Define double fertilization.
2. Name the male and female reproductive units of a flower.
3. What is apomixis?
4. How many nuclei are present in the embryo sac?
5. Name the parts of carpel.

2–3 Marks Questions

6. Differentiate between microsporogenesis and megasporogenesis.
7. What is the significance of pollination?
8. Explain the process of triple fusion.
9. Describe the role of endosperm.
10. What are the advantages of cross-pollination?

5 Marks / Long Answer Questions

11. Explain the process of double fertilization in flowering plants with a labeled diagram.
12. Describe the post-fertilization changes that occur in an angiosperm flower.
13. Compare self-pollination and cross-pollination.

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Previous Year Questions (PYQs)

Year	Question	Marks
2025 (Sample)	Describe double fertilization. Why is it unique to angiosperms?	5
2024	Differentiate between apomixis and sexual reproduction.	3
2023	Explain structure of a typical angiosperm ovule.	3
2022	What are synergids? State their role in fertilization.	2
2021	What happens to the ovary and ovule after fertilization?	2

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Key Definitions

Term	Definition
Microsporogenesis	Formation of microspores (pollen grains) from microspore mother cell.
Megasporogenesis	Formation of megaspore from megaspore mother cell.
Double Fertilization	Fusion of one male gamete with egg and another with two polar nuclei.
Endosperm	Triploid tissue that nourishes the embryo.
Apomixis	Formation of seeds without fertilization.
Polyembryony	Development of multiple embryos in one seed.

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Tips for Exam Success

• Revise all NCERT diagrams: structure of anther, ovule, embryo sac, and double fertilization.
• Use keywords like “syngamy,” “triple fusion,” “endosperm.”
• Practice labeled diagrams for visual questions.
• Write definition + example for every short answer.
• Solve previous year questions and CBSE sample papers.

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Frequently Asked Questions (FAQs)

Q1. Why is double fertilization called unique to angiosperms?
Because it involves two fusions — one forms zygote and the other forms endosperm — a feature not seen in any other group of plants.

Q2. What is the role of endosperm?
Endosperm nourishes the developing embryo with nutrients like starch and proteins.

Q3. What is the function of synergids?
Synergids guide the pollen tube toward the egg cell for fertilization.

Q4. Which part of flower forms fruit?
The ovary forms the fruit, while the ovules become seeds.

Q5. Give one example each of monocot and dicot seed.
Maize – monocot; Pea – dicot.

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Final Summary for Revision

• Sexual reproduction in plants occurs in flowers.
• Microsporogenesis → pollen grain; Megasporogenesis → embryo sac.
• Pollination transfers pollen to stigma.
• Double fertilization = Syngamy + Triple fusion.
• Post-fertilization: Zygote → Embryo → Seed → Fruit.
• Apomixis & polyembryony = variations of reproduction.

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Conclusion

“Sexual Reproduction in Flowering Plants” is the foundation of plant reproduction biology. Understanding this chapter thoroughly helps students perform well in CBSE Board exams and builds strong conceptual clarity for NEET Biology.
Focus on processes, diagrams, and terminologies — they hold the key to full marks.

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