Class 12 Biology Project File Topic: Sexual Reproduction in Flowering Plants
Submitted by: [Your Name]
Class: XII – Science
Roll No.: ______
School Name: ______
Academic Year:** 2024–2025
Index
1. Introduction
2. Objectives
3. Flower Structure
4. Pre-fertilization Events
5. Pollination
6. Fertilization
7. Post-fertilization Changes
8. Seed and Fruit Formation
9. Significance of Sexual Reproduction
10. Conclusion
11. Bibliography
1. Introduction
Sexual reproduction in flowering plants, also known as angiosperms, is a highly organized and complex
biological process that ensures the continuation of plant species from generation to generation. This
type of reproduction involves the formation and fusion of male and female gametes, resulting in the
development of a zygote, which ultimately gives rise to a new plant. The reproductive process is carried
out in specialized structures called flowers, which contain both male (stamen) and female (carpel)
organs.
The process begins with the development of reproductive cells (gametogenesis), followed by
pollination, where pollen grains are transferred from the anther to the stigma. Once the pollen reaches
the stigma, fertilization occurs through the formation of a pollen tube that delivers the male gametes to
the female gametophyte. A distinctive feature of angiosperms is the occurrence of double fertilization,
which leads to the formation of both the embryo and the endosperm that nourishes it.
After fertilization, the ovary transforms into a fruit, and the ovules develop into seeds. These seeds
serve as the propagating units and contain the embryo that grows into a new plant under favorable
conditions. This method of reproduction is essential for genetic diversity, adaptability, and evolution
among plant species. It also plays a crucial role in agriculture, horticulture, and food production, as it
leads to the formation of fruits and seeds that are vital for human consumption.
1
2. Objectives
• To study the structure and function of reproductive organs in flowers.
• To understand the events before and after fertilization.
• To learn the mechanisms of pollination and types of pollinating agents.
• To explore the development of seed and fruit.
• To appreciate the importance of genetic variation in plants.
3. Flower Structure
Flowers are the reproductive structures of angiosperms. A complete flower has four whorls: - Calyx:
Outermost whorl; composed of sepals. - Corolla: Second whorl; made of petals, often brightly colored. -
Androecium: Male reproductive part consisting of stamens. Each stamen has an anther and filament. -
Gynoecium: Female reproductive part made up of one or more carpels. Each carpel contains an ovary,
style, and stigma.
Function of Flower Parts: - Anther produces pollen grains (male gametophytes). - Ovary contains
ovules where female gametophytes develop.
4. Pre-fertilization Events
a) Gametogenesis
• Microsporogenesis: Formation of microspores (pollen grains) inside anthers.
• Megasporogenesis: Formation of megaspores within the ovule.
b) Gamete Formation
• Male Gamete: Each pollen grain contains two nuclei; one is a generative nucleus which divides
to form two male gametes.
• Female Gamete: The functional megaspore undergoes mitotic divisions to form the embryo sac
containing the egg cell.
5. Pollination
Pollination is the transfer of pollen grains from the anther to the stigma. It is a crucial step for
fertilization.
Types of Pollination
• Autogamy: Self-pollination within the same flower.
• Geitonogamy: Transfer between different flowers of the same plant.
• Xenogamy: Cross-pollination between flowers of different plants.
2
Pollinating Agents
• Abiotic: Wind (anemophily), Water (hydrophily)
• Biotic: Insects (entomophily), Birds (ornithophily), Bats (chiropterophily)
Adaptations like nectar, scent, and colorful petals attract biotic agents.
6. Fertilization
Fertilization in flowering plants involves the fusion of male and female gametes. It takes place after
successful pollination.
Double Fertilization
• Pollen grain germinates on the stigma and forms a pollen tube.
• Tube enters the ovule through the micropyle.
• One male gamete fuses with the egg (syngamy) forming a zygote.
• The other fuses with two polar nuclei (triple fusion) forming the primary endosperm nucleus
(PEN).
This unique process is called double fertilization, a hallmark of angiosperms.
7. Post-fertilization Changes
• Zygote develops into an embryo.
• Ovule transforms into a seed.
• Ovary enlarges to become a fruit.
• Integuments form the seed coat.
• The endosperm may develop to nourish the growing embryo.
8. Seed and Fruit Formation
Seed
• Consists of an embryo (radicle, plumule, cotyledons), endosperm (in some seeds), and a
protective seed coat.
• Seeds are dispersed by wind, water, and animals.
Fruit
• Fruit is the mature ovary containing seeds.
• True fruits develop only from the ovary.
• False fruits involve other floral parts (e.g., apple).
3
9. Significance of Sexual Reproduction
• Produces offspring with genetic variation.
• Increases adaptability and survival of species.
• Essential for crop improvement and hybrid development.
• Helps in natural selection and evolution.
10. Conclusion
Sexual reproduction in flowering plants is a highly evolved process ensuring the perpetuation and
variation of plant species. From gamete formation to fruit development, each step is intricately
coordinated. Understanding this process is vital for biology students and crucial for advances in
agriculture and horticulture.
11. Bibliography
• NCERT Class 12 Biology Textbook
• Trueman’s Elementary Biology Vol 2
• Biologydiscussion.com
• YourBiologyNotes.com
• Class notes and lab manuals
