Скачать или смотреть Double Fertilization in Angiosperms : A journey Through Pollen Explained In Hindi

Double Fertilization in Angiosperms : A journey Through Pollen Explained In Hindi
Double fertilization is a unique and complex process of fertilization that occurs exclusively in angiosperms, or flowering plants. It involves two separate fusion events, which are crucial for the formation of both the embryo and the nutritive tissue that supports its development.

The Process of Double Fertilization
The process begins with the pollination of a flower, followed by the germination of the pollen grain.

1. Pollen Germination and Pollen Tube Growth:
When a pollen grain lands on the stigma of a compatible flower, it germinates and forms a pollen tube. This tube grows down through the style and into the ovary, a process guided by chemical signals from the ovule.

2. The Male Gametes:
The pollen grain contains a vegetative cell and a generative cell. The generative cell divides to produce two sperm cells, which are the male gametes. These two sperm cells travel down the pollen tube towards the ovule.

3. Entry into the Ovule:
The pollen tube enters the ovule through a small opening called the micropyle. It then discharges the two sperm cells into the embryo sac (also known as the female gametophyte), which is a seven-celled, eight-nucleate structure containing the female gametes and other specialized cells.

4. The Two Fertilization Events:
Once inside the embryo sac, the two sperm cells participate in two distinct fertilization events:

First Fertilization (Syngamy): One of the sperm cells fuses with the egg cell (the female gamete). This fusion forms a diploid zygote (2n). The zygote will then undergo mitosis to develop into the embryo, which will eventually become the new plant.

Second Fertilization (Triple Fusion): The second sperm cell migrates and fuses with the two polar nuclei located in the central cell of the embryo sac. This fusion forms a triploid (3n) primary endosperm nucleus. This nucleus will then divide and differentiate into the endosperm, a nutrient-rich tissue that provides food and energy to the developing embryo.

The Significance of Double Fertilization
The unique nature of double fertilization provides several key advantages for angiosperms:

Synchronized Development: The formation of the embryo and the endosperm happens simultaneously. This ensures that the food source is available immediately to support the embryo's growth, maximizing the efficiency of energy and resource use.

Parental Investment Control: By forming the endosperm only after fertilization, the plant avoids wasting resources on an unfertilized ovule. This is more efficient compared to gymnosperms (like conifers), where the nutritive tissue is formed before fertilization, regardless of whether a fertilization event occurs.

Genetic Diversity: Both the embryo and the endosperm are genetically distinct from the parent plant, with the embryo being a combination of genes from both parents and the endosperm having a unique triploid genome.

Embryo and Endosperm Relationship: The endosperm can be a crucial source of nutrition for the embryo throughout its development. In some plants (like rice and corn), the endosperm remains in the mature seed as a primary food source. In others (like beans), the endosperm's nutrients are absorbed by the embryo's cotyledons, which then act as the food storage for the developing seedling.

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