Question

Как происходит двойное оплодотворение у цветковых растений? ПРОШУ ПОМОГИТЕ

Answer 1

Ответ:

ответ

Объяснение:

Суть двойного оплодотворения заключается в том, что один из спермиев сливается с яйцеклеткой (оплодотворяет ее) с образованием зиготы (диплоидна), из которой развивается зародыш. Второй спермий сливается с центральной клеткой (эта клетка к моменту слияния уже диплоидна) с образованием эндосперма (триплоиден) - запасного питательного вещества. После оплодотворения с течением времени из семязачатков образуются семена.

Answer 2

Double Fertilization in Flowering Plants

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 both a zygote and endosperm. Let's explore the process in more detail.

The Male Gametophyte

In flowering plants, the male gametophyte is called pollen. It develops within the anther, which is part of the flower's reproductive structure called the stamen. Each pollen grain contains two sperm cells.

The Female Gametophyte

The female gametophyte, also known as the embryo sac, develops within the ovule, which is located within the flower's ovary. The embryo sac contains two female gametes: the egg cell and the central cell.

Pollination

Pollination is the transfer of pollen from the anther to the stigma, which is part of the flower's female reproductive structure called the pistil. This can occur through various means, such as wind, water, or animal pollinators.

Double Fertilization Process

1. Pollen Tube Formation: After pollination, the pollen grain germinates on the stigma and forms a pollen tube. The pollen tube grows down through the style, a long tube-like structure connecting the stigma and ovary.

2. Entry of Pollen Tube into the Ovule: The pollen tube continues to grow and eventually reaches the ovule. It enters through a small opening called the micropyle.

3. Delivery of Sperm Cells: Once inside the ovule, the pollen tube releases the two sperm cells. One sperm cell fertilizes the egg cell, forming a zygote, which will develop into the embryo. This is the process of syngamy.

4. Fusion with the Central Cell: The second sperm cell fuses with the central cell of the embryo sac. This fusion results in the formation of endosperm, a nutrient-rich tissue that provides nourishment to the developing embryo. This process is called triple fusion because it involves the fusion of two sperm cells with two different female gametes.

Significance of Double Fertilization

Double fertilization is a unique feature of flowering plants and has several important functions:

1. Embryo Development: The fertilized egg cell develops into an embryo, which eventually grows into a new plant.

2. Endosperm Formation: The fusion of the second sperm cell with the central cell leads to the formation of endosperm. Endosperm provides nutrients to the developing embryo and is essential for seed development and germination.

3. Prevention of Polyploidy: Double fertilization ensures that the ploidy levels of the embryo and endosperm are balanced. The embryo is diploid (2n), while the endosperm is triploid (3n). This prevents polyploidy, which can lead to developmental abnormalities.

4. Efficient Resource Allocation: The endosperm serves as a nutrient reserve for the developing embryo, ensuring its proper growth and development.

In conclusion, double fertilization is a unique reproductive process in flowering plants. It involves the fusion of two sperm cells with two different female gametes, resulting in the formation of both a zygote and endosperm. This process ensures the successful development of the embryo and efficient resource allocation for the growing plant.