Explain double fertilisation?

Question

Answer

Double fertilization is a characteristic feature of flowering plants. In the process of double fertilization out of the two sperm nucleus, one sperm nucleus fuses with the egg nucleus to form an embryo ( process is called syngamy) and another fuses with polar nuclei to form endosperm ( process is called triple fusion). Since two kinds of fusion—syngamy and triple fusion—take place, the process is known as double fertilisation...

Answer

Double fertilization is a complex fertilization mechanism of flowering plants. This process involves the joining of a female gametophyte with two male gametes. It begins when a pollen grain adheres to the stigma of the carpel, the female reproductive structure of a flower.

Answer

Double fertilization - Sexual Reproduction in Flowering Plants, Biology, Class 12

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Answer

Double fertilization is a unique reproductive process that occurs in flowering plants (angiosperms). It involves the fusion of two sperm cells with two different female gametes, resulting in the formation of a zygote and endosperm. This process is crucial for the successful development of seeds in angiosperms.

The Process of Double Fertilization:

1. Pollination: Pollination is the first step in double fertilization. It involves the transfer of pollen grains from the anther (male reproductive structure) to the stigma (female reproductive structure) of a flower. This can occur either through self-pollination (transfer of pollen from the same flower or plant) or cross-pollination (transfer of pollen from a different flower or plant).

2. Gamete Formation: Inside the anther, diploid cells called microsporocytes undergo meiosis to produce four haploid microspores. Each microspore then develops into a pollen grain, which contains a tube cell and two sperm cells. In the ovule, a diploid cell called the megasporocyte also undergoes meiosis to produce four haploid megaspores. However, only one megaspore survives and develops into the female gametophyte.

3. Pollen Tube Formation: After pollination, the pollen grain lands on the stigma and germinates, forming a pollen tube. The tube cell of the pollen grain elongates and grows down through the style, towards the ovule, guided by chemical signals.

4. First Fertilization: As the pollen tube reaches the ovule, it enters through a small opening called the micropyle. One of the two sperm cells inside the pollen tube fuses with the egg cell (female gamete) located in the embryo sac, forming a diploid zygote. This is known as the first fertilization, and it results in the formation of the embryo, which will develop into the new plant.

5. Second Fertilization: Simultaneously, the second sperm cell fuses with two polar nuclei (two other female gametes) present in the embryo sac. This fusion forms a triploid nucleus, which undergoes mitosis to produce the endosperm. The endosperm serves as a nutrient-rich tissue that nourishes the developing embryo.

Significance of Double Fertilization:

- Ensures efficient utilization of resources: Double fertilization allows angiosperms to produce both the embryo and the endosperm, which ensures efficient utilization of resources and increases the chances of successful seed development.

- Provides nourishment to the developing embryo: The endosperm, produced through the second fertilization, provides essential nutrients to the developing embryo, promoting its growth and development.

- Promotes genetic diversity: The fusion of two different sperm cells with two female gametes results in the formation of a genetically diverse offspring. This genetic diversity enhances the adaptability and survival of angiosperms in various environments.

In conclusion, double fertilization is a unique reproductive process in flowering plants that involves the fusion of two sperm cells with two different female gametes. This process ensures the development of both the embryo and the endosperm, providing nourishment and genetic diversity, which are crucial for the successful reproduction and survival of angiosperms.

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