Sexual Reproduction in Flowering Plants

Notes

1. Introduction

Sexual reproduction in flowering plants is the process by which new plants are produced through the fusion of male and female gametes. It results in the formation of seeds and fruits.

Importance

Produces genetic variation.

Ensures continuity of species.

Helps plants adapt to changing environments.

Forms healthy and vigorous offspring.

2. Stages of Sexual Reproduction

Sexual reproduction occurs in three stages:

A. Pre-fertilization Events

Gamete formation

Pollination

B. Fertilization

Fusion of male and female gametes

Double fertilization

C. Post-fertilization Events

Endosperm formation

Embryo development

Seed formation

Fruit formation

3. Flower – Reproductive Organ

Flower is the reproductive organ of angiosperms.

It consists of four whorls

Whorl Function

Calyx Protects flower bud

Corolla Attracts pollinators

Androecium Male reproductive part

Gynoecium Female reproductive part

4. Androecium (Male Reproductive Part)

Androecium consists of stamens.

Each stamen has:

Filament

Anther

Structure of Anther

Bilobed

Dithecous

Four pollen sacs (Microsporangia)

Each microsporangium contains:

Epidermis

Endothecium

Middle layers

Tapetum

Sporogenous tissue

5. Tapetum

Tapetum is the innermost layer of the anther.

Functions

Nourishes developing pollen grains.

Produces enzymes.

Helps in pollen wall formation.

Provides proteins to pollen grains.

Important Board Point: Tapetum is rich in nutrients.

6. Microsporogenesis

Formation of microspores from Microspore Mother Cell (MMC).

Process

Microspore Mother Cell (2n)

↓

Meiosis

↓

Four Haploid Microspores (n)

↓

Pollen Grains

7. Pollen Grain

Pollen grain is the male gametophyte.

Structure

Outer Wall → Exine

Made of Sporopollenin

Highly resistant

Inner Wall → Intine

Made of Cellulose & Pectin

Contains:

Vegetative Cell

Generative Cell

Generative cell divides to form two male gametes.

8. Pollen Viability

The ability of pollen grains to remain alive.

Examples:

Rice → 30 minutes

Wheat → Few hours

Rosaceae → Several months

9. Pollen Bank

Storage of pollen grains in liquid nitrogen.

Temperature:

−196°C

Importance:

Plant breeding

Hybrid seed production

10. Gynoecium (Female Reproductive Part)

Made up of carpels.

Each carpel has:

Stigma

Style

Ovary

Inside ovary are Ovules.

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