Sexual Reproduction in Flowering Plants Notes Class 12

*As per the latest CBSE syllabus 2023-24, this chapter has been renumbered as Chapter 1 in NCERT*

CBSE Class 12 Sexual Reproduction in Flowering Plants: Sexual reproduction in flowering plants plays an important role in plant species from one geographic region to another. When male and female gametes of a plant fuse, the process is known as sexual reproduction. After fertilization, the ovule develops into a seed. 

Sexual reproduction in flowering plants notes Class 12 helps you learn about this process and how it contributes to the genetic diversity of plants. Also, find the Sexual Reproduction in Flowering Plants NCERT Solutions Class 12 here. You can find the CBSE Class 12 Sexual Reproduction in Flowering Plants Notes.

Sexual Reproduction in Flowering Plant

Flowers are the main part and play an important role in the sexual reproduction of plants. Sexual reproduction in plants occurs when the fusion of male and female gametes occurred. The male reproductive part of the flower is known as the androecium, and the female reproductive part is known as the gynoecium. These both can be present in the same flower or male in one and female part in another flower. Zygote is formed after the fusion of male and female gametes. Zygoted developed in seed which further developed in fruit.

Structure of Flower

The structure of flower consists of several key parts:

• Petals – Provide color and attract pollinators
• Sepals – Protect the flower bud before it blooms
• Stamen – Comprising the anther and filament, which produce pollen
• Pistil – Consisting of the stigma, style, and ovary, where seeds develop after pollination.

Each part of flower plays a vital role in the flower’s reproductive process, ensuring the continuation of plant species through pollination and seed formation.

Reproductive Structure of Flower

Two types of reproductive structures are present in the flower i.e., Androecium and Gynoecium.

Androecium

The androecium is the male reproductive part of the plant. The androecium consists of whorls of stamens. A stamen consists of the filament (long and slender stalk) and anther (the terminal bilobed structure). Each lobe is dithecous (2 thecae). Theca is separated by a longitudinal groove running lengthwise. The anther is a tetragonal structure consisting of 4 microsporangia/microsporangium located at the corners 2 in each lobe. The microsporangia develop further and become pollen sacs that are packed with pollen grain.

Pollen Grains

Pollen grain represents the male gamete and is spherical having a two-layered wall.

• Outer exine: Hard layer made of sporopollenin which is extremely resistant and can withstand high temperatures, acidic, alkaline conditions, and enzymes.
• Inner intine: It is a thin and continuous layer made up of cellulose and pectin.
• A mature pollen grain contains two cells.
  • Vegetative cell: It is bigger in size and reserves food and a large nucleus.
  • Generative cell: It is small in size and floats in the cytoplasm of the vegetative cell. It has a nucleus and it mitotically divides to form 2 male gametes.

Gynoecium

The gynoecium represents the female reproductive part of a flower. It consists of whorls of pistils. Each pistil has three parts.

• Stigma: It is a landing platform for pollen grains
• Style: It is a long slender part below the stigma
• Ovary: It is a basal swollen part of the pistil. Inside the ovary, there is a tissue called the placenta upon which ovules are developing. The number of ovules in the ovary may be one or many. The ovary has one or more cavities called locules.

Megasporangium/Ovule

The ovule is attached to the placenta by a stalk (Funicle). The junction where the body of the ovule and funicle fuse is called the hilum. Each ovule has one or two protective envelopes called integuments which cover the rest of the ovule except for a small opening called the micropyle.

Megasporangium Diagram

Opposite the micropyle end, is the Chalaza which represents the basal part of the ovule. The mass of cells that are enclosed within the integuments is called the nucleus. It contains reserved food materials. The embryo sac or female gametophyte is located within the nucleus.

Formation of Embryosac

The nucleus of the functional megaspore divides mitotically to form two nuclei which move toward the opposite pole and form 2 nucleate embryosac. Two more sequential mitotic nuclear divisions ensure leading to the 8 nuclei and 8 nucleate embryo sac each opposite end has a 4 nucleus group.

Distribution of the Cell Within the Embryo Sac

• 6 of the 8 nuclei get surrounded by the cell wall and the remaining two called polar nuclei are situated at the center.
• 3 of the 6 cells are grouped together at the micropylar pole and constitute the egg apparatus (it consists of 2 synergids and one egg cell). The synergids have Filiform apparatus which guides the pollen tubes into the synergid.
• The other 3 cells at the chalazal end are called the antipodals.
• Thus, a typical mature angiosperm embryo is 8 nucleates and 7 cells.

Pollination

Pollination is a course of moving the dust/pollen grains across the anther and the stigma of a similar flower of a plant or to various plants for the process of fertilization and the creation of seeds. The specialists engaged in moving the pollen grains are birds, wind, creatures, and water.

Autogamy (self-pollination)– It is the transfer of pollen grain from another to the stigma of the same flower. It requires the anther and stigma to lie closely. Plants like viola, oxalis, and commelina produce 2 types of flowers.

• Chasmogamous (Open flower) – Flowers with exposed anthers and stigma.
• Cleistogamous (close flower)- Flowers that do not open at all.
• Geitonogamy (Cross pollination) – It is the process of transfer of pollen grain from the anther of one flower to the stigma of another flower in the same plant. It requires a pollination agent.
• Xenogamy (cross-pollination)- It is the process of the transfer of pollen grain from anther to the stigma of a different plant. This brings a genetic difference.

Fertilization

After entering into synergids, the pollen tube releases 2 male gametes into the cytoplasm of the synergies.

Syngamy: One of the male gametes fused with the egg cell forms the zygote (2n) and develops into an embryo.

Male gamete (n) + Egg cell (n) —- Zygote (2n) —Embryo—Plant (2n)

Triple fusion: The other male gametes fuses with 2 polar nuclei to produce a triploid primary endosperm nucleus and develops into the endosperm.

Male gamete (n) + 2 polar nuclei (n+n) —primary endosperm nucleus (3n) –Endosperm (3n)

The fusion of syngamy and triple fusion that occur in the embryo sac is termed double fertilization.

Post-fertilization

Following double fertilization, the event of endosperm and embryo development, maturation of ovule into seed, and ovary into fruit are collectively termed post-fertilization events.

Endosperm

Endosperm cells are filled with reserved food materials. They are used for the nutrition of the developing embryo. Steps of endosperm development

• Step-1 Primary endosperm nucleus undergoes successive nuclear divisions to give rise to free nuclei. This is called a free nuclear endosperm.
• Step-2 Subsequently cell wall formation occurs and the endosperm becomes cellular. The tender coconut water is a free nuclear endosperm and the surrounding white kernel is the cellular endosperm.

CBSE Previous Year Question Papers

Learn from CBSE Previous Year Question Papers to boost your understanding and excel in your studies.

CBSE Class 12 Previous Year Question Paper for Biology (2022)	CBSE Class 12 Physics Previous Year Question Paper 2022
CBSE Previous Year Question Papers Class 10 Biology – 2023	CBSE Class 12 Chemistry Previous Year Question Paper 2022
CBSE Class 10 Previous Year Question Paper (Biology) – 2020	Previous Year Question Paper for CBSE Class 12 Biology – 2020

FAQs on Sexual Reproduction in Flowering Plants Notes Class 12

What are the 6 Steps of Sexual Reproduction in Flowering Plants?

Following are the 6 essential steps of sexual reproduction in plants – pollination, fertilization, seed development, fruit development, seed disperal, and germihnation.

Which Plant Dies after Flowering?

Plants that die after flowering are monocarpous flowers. Example: Alphonse De Candolle

What are the Sexual Reproduction in Flowering Plants Events?

Sexual reproduction in flowering plants involves pollination, fertilization, seed development, fruit development, seed dispersal, and germination, ensuring the continuation of the plant species.

Why Vegetative Reproduction is also Considered a Type of Asexual Reproduction?

Vegetative reproduction is a cycle during which new plants are obtained without the get-together of seeds or spores. It includes the engendering of plants through specific vegetative parts like the rhizome, sucker, tuber, bulb, and so on. 

What is the Sexual Reproduction in Flowering Plants Notes?

Sexual reproduction in flowering plants involves the fusion of male and female gametes to form seeds, facilitated by pollination, fertilization, and seed dispersal mechanisms, vital for genetic diversity and plant propagation.

Where can I Find the Class 12 Sexual Reproduction in Flowering Plants Notes?

You can find well crafted notes on sexual reproduction in flowering plants at the top of this article.

What is Meant by Pre-Fertilisation?

Pre-fertilization encompasses processes like pollination and gamete formation before actual fertilization occurs in plants, ensuring successful reproduction.

What is an Embryo Sac?

An embryo sac is the female gametophyte in angiosperms, containing the egg cell and synergids, crucial for fertilization and seed development.

What are the Important Features and Topics Covered in Class 12 Biology Revision Notes Chapter 2?

Class 12 Biology Notes on Chapter 2 Sexual Reproduction in Flowering Plant cover topics such as sexual reproduction in flowering plants, including flower structure, pollination mechanisms, fertilization processes, and seed formation, emphasizing key concepts and mechanisms in plant reproduction

What are the Benefits of Referring to NCERT Class 12 Revision Notes Biology Chapter 2?

Referring to NCERT Class 12 Biology Chapter 2 revision notes helps in comprehensive understanding, clarifying concepts, and reinforcing key topics for effective exam preparation.