What is Double Fertilisation in Angiosperms?
Double fertilisation is a special form of fertilisation that occurs in flowering plants (angiosperms). It involves the fusion of two male gametes (sperm cells) with different female reproductive components. This process ensures that both a zygote and an endosperm are formed, which are essential for the development of seeds.
In flowering plants, also known as angiosperms, reproduction involves a fascinating process called double fertilisation. This unique and crucial event helps plants develop seeds and fruits, ensuring the next generation of plants. In this article, we will break down the process of double fertilisation, its significance in plants, and why it is essential for the growth and development of seeds and fruits.
Key Steps in Double Fertilisation:
Pollination: Pollen grains carrying male gametes land on the stigma of the female flower.
Pollen Tube Formation: The male gametes travel through the style and enter the ovary.
Fertilisation: One sperm fertilises the egg cell, forming a zygote (2n). The second sperm fuses with two polar nuclei, forming the endosperm (3n).
This two-step fertilisation process is what we call double fertilisation in angiosperms. The zygote develops into an embryo, and the endosperm serves as a food reserve for the developing embryo.
Also Read: Pollination
The Process of Double Fertilisation in Angiosperms
Let's look at the step-by-step process of double fertilisation in plants:
Pollination: The first step in fertilisation is pollination, where pollen grains from the male part (anthers) are transferred to the female part (stigma) of the flower.
Germination of Pollen Grain: After pollination, the pollen grain germinates, forming a pollen tube that grows down the style toward the ovary. The pollen tube carries two sperm cells.
Fertilisation:
Syngamy: One of the sperm cells fuses with the egg cell in the ovule, forming a zygote.
Triple Fusion: The second sperm cell fuses with two polar nuclei in the central cell, forming the primary endosperm nucleus (PEN), a triploid (3n) structure.
Zygote and Endosperm Development: The zygote will develop into the embryo, while the PEN becomes the endosperm, nourishing the growing embryo inside the seed.
Significance of Double Fertilisation in Angiosperms
Double fertilisation plays a vital role in the reproductive success of flowering plants. Here are the key reasons why it is significant:
Efficient Resource Allocation: Double fertilisation ensures that the resources are used optimally for seed development. The formation of both a zygote and an endosperm ensures the embryo gets nourishment as it grows.
Seed Viability: The endosperm created during the process provides essential nutrients to the developing embryo, increasing seed viability and the plant's chance of survival.
Development of Fruits and Seeds: The fertilised ovule develops into a seed, and the ovary forms a fruit, both crucial for the plant's reproduction and dispersal.
Polyembryony: In some cases, double fertilisation may result in polyembryony, where multiple embryos are formed, increasing the plant's chances of successful reproduction.
Double Fertilisation Diagram
Here’s a simple double fertilisation diagram to help you visualise the process:
Pollen grain lands on the stigma.
The pollen tube grows through the style and into the ovary.
One sperm cell fertilises the egg cell, forming the zygote.
The second sperm cell fuses with the polar nuclei, forming the endosperm.
Unique Aspects of Double Fertilisation
Besides fertilising the egg to form the zygote and the polar nuclei to form the endosperm, double fertilisation has some unique aspects that are not seen in many other plant species, such as gymnosperms (conifers). The fusion of two male gametes ensures that both the embryo and the nutritive tissue (endosperm) are formed in the seed, which is vital for the proper growth of the seedlings after germination.
Conclusion
Double fertilisation in angiosperms is a fascinating process that ensures the development of viable seeds and fruits, ultimately leading to the successful reproduction of plants. Understanding its process, significance, and the formation of both zygote and endosperm helps us appreciate the intricacies of plant biology.
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FAQs on Double Fertilisation in Angiosperms: A Key to Plant Reproduction
1: What is double fertilisation?
Double fertilisation refers to the fusion of one female gamete (egg cell) with two male gametes (sperm cells), resulting in the formation of both a zygote (embryo) and an endosperm (food source).
2: Why is double fertilisation important in plants?
It plays a critical role in seed formation, polyembryony, and increasing seed viability by ensuring that both the embryo and the endosperm are formed, thus supporting the growth of the next generation.
3: What are the end products of double fertilisation?
The end products of double fertilisation are the diploid zygote and the triploid primary endosperm nucleus (PEN), which later develops into the endosperm that nourishes the growing embryo.
4: How does double fertilisation differ in gymnosperms?
Gymnosperms do not undergo double fertilisation because their reproductive structures are different from angiosperms. They lack ovaries, and pollination occurs via wind, not through the fusion of pollen grains with female gametes.
