Post-Fertilization Events in Angiosperms
After fertilization, the ovule develops into a seed, and the ovary transforms into a fruit. Several key processes occur, including embryogenesis, endosperm formation, and fruit development.
A. Development of Embryo and Seed
1. Embryogenesis (Formation of Embryo)
Embryogenesis is the process by which the zygote (2n) develops into a mature embryo.
It occurs inside the seed and involves cell division and differentiation.
The embryo consists of:
Radicle (develops into the root).
Plumule (develops into the shoot).
Cotyledons (seed leaves, store food).
Diagram: Development of Dicot and Monocot Embryos
(Illustration of dicot (e.g., Pea) and monocot (e.g., Maize) embryos showing radicle, plumule, and cotyledons.)
2. Structure of a Seed
A seed is the mature ovule after fertilization.
It contains:
Seed coat (protective outer covering).
Embryo (future plant).
Endosperm (nutritive tissue in some seeds).
Dicot vs. Monocot Seed Differences:
| Feature | Dicot Seed (e.g., Bean, Pea) | Monocot Seed (e.g., Maize, Wheat) |
|---|---|---|
| Cotyledons | Two | One |
| Endosperm | Absent in mature seed (used up during development) | Present in mature seed (stores food) |
| Example | Pea, Gram, Bean | Maize, Rice, Wheat |
Diagram: Structure of Dicot and Monocot Seeds
(Illustration showing seed coat, cotyledons, radicle, plumule, and endosperm in dicot and monocot seeds.)
B. Endosperm Formation
The endosperm provides nutrients to the developing embryo.
It is formed by the fusion of one male gamete (n) with two polar nuclei (n + n) → Triploid endosperm (3n).
Types of Endosperm Formation:
| Type | Description | Example |
|---|---|---|
| Nuclear Endosperm | Free nuclei divide without cell wall formation, later forming a cellular structure. | Coconut (liquid endosperm), Maize |
| Cellular Endosperm | Cell walls form after every nuclear division, leading to a fully cellular endosperm. | Datura, Petunia |
| Helobial Endosperm | Partly nuclear and partly cellular; an initial division produces two cells, one grows faster. | Asphodelus |
Diagram: Types of Endosperm Formation
(Illustration showing nuclear, cellular, and helobial endosperm development.)
C. Fruit Formation
After fertilization:
The ovary develops into a fruit.
The ovule becomes the seed.
The fruit protects the seed and aids in dispersal.
Types of Fruits:
| Type | Definition | Examples |
|---|---|---|
| Simple Fruit | Develops from a single ovary of a single flower. | Mango, Tomato, Pea |
| Aggregate Fruit | Develops from multiple ovaries of a single flower. | Strawberry, Raspberry |
| Multiple (Composite) Fruit | Develops from ovaries of multiple flowers in an inflorescence. | Pineapple, Jackfruit |
Diagram: Types of Fruits with Examples
(Illustration showing simple, aggregate, and multiple fruit types.)
Conclusion
The post-fertilization events ensure the successful development of the embryo, seed, and fruit. Endosperm formation nourishes the embryo, while fruit formation helps in seed dispersal, ensuring the continuity of plant species.