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Twelve Standard >> Sexual reproduction in plants | Part - 1

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Formation Of Microsporogenesis and its process

 

Sexual reproduction in angiosperms involves the formation of male and female gametes through two processes: microsporogenesis and megasporogenesis. These processes occur within the reproductive structures of flowers, leading to the production of pollen grains (male gametes) and embryo sacs (female gametes), respectively.

Reproduction in plants

Microsporogenesis: Formation of Microspores (Pollen)

  1. Formation of Pollen Sac: Within the anther of the flower's stamen, microsporogenesis takes place. Each anther typically contains four pollen sacs, which are referred to as a tetrad.

  2. Diploid Mother Cells: Within each pollen sac, diploid cells called microsporocytes or pollen mother cells are present.

  3. Meiosis: Each microsporocyte undergoes meiosis, a specialized cell division process, resulting in the formation of four haploid microspores. Meiosis halves the chromosome number, ensuring that each microspore contains half the genetic material of the parent cell.

  4. Development of Pollen Grains: The microspores develop further and undergo significant structural changes, leading to the formation of pollen grains. The mature pollen grain consists of two cells: the generative cell and the tube cell.

  5. Outer Layers: The pollen grain is protected by the outer layers, collectively known as the exine and intine. The exine is made of a tough and resistant substance called sporopollenin, which helps protect the pollen grain during its dispersal.

  6. Release of Pollen: Once mature, the pollen grains are released from the anther and can be transported to the stigma of a flower (pollination) to fertilize the ovule.

Pollen Grain Structure and Composition:

  1. Exine: The outer layer of the pollen grain is called the exine. It is made of a tough and resistant substance known as sporopollenin. Sporopollenin protects the pollen grain from environmental stresses, such as desiccation and microbial attack, ensuring its viability during dispersal.

  2. Intine: Beneath the exine is the intine, which is the inner layer of the pollen grain. The intine is made up of a more delicate and flexible material.

  3. Generative Cell: The generative cell is one of the two cells present in the pollen grain's cytoplasm. It plays a crucial role in the process of double fertilization.

  4. Tube Cell: The second cell present in the pollen grain is the tube cell. After pollination, this cell elongates to form the pollen tube, which grows through the style of the flower to reach the ovary and deliver the generative cell and sperm cells to the embryo sac for fertilization.

Pollen Kit:

The term "pollen kit" is used to refer to the mature pollen grain along with its protective exine, the generative cell, and the tube cell. It represents the fully developed male gametophyte of the angiosperms.

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