Question: Explain the monosporic development of embryo sac in the ovule of an angiosperm.
The correct answer is –
The development of the embryo sac in the ovule of an angiosperm plant is a complex process that involves the formation of several cells through mitotic division. Monosporic development is a type of embryo sac development that occurs in about 70% of angiosperm species.
The process of monosporic development of the embryo sac can be divided into several stages:
- Megaspore mother cell (MMC): The process begins with the formation of a megaspore mother cell (MMC) within the ovule. The MMC undergoes meiosis to produce four haploid cells.
- Functional megaspore: Three of the four cells produced by meiosis degenerate, and only one of them develops into a functional megaspore.
- Mitotic division: The functional megaspore undergoes three rounds of mitotic division, resulting in the formation of eight haploid nuclei, which are enclosed in a single cell.
- Cell differentiation: The eight nuclei undergo differentiation to form three distinct cell types: the egg cell, two synergids, and three antipodal cells.
- Polar nuclei fusion: The two polar nuclei located at the center of the embryo sac fuse to form a diploid nucleus called the secondary nucleus.
The resulting structure is the mature embryo sac or female gametophyte, which is a seven-celled structure with eight haploid nuclei. The egg cell, which is located at one end of the embryo sac, is the female gamete that fuses with the male gamete during fertilization to form the zygote, which develops into the embryo.
In summary, the monosporic development of the embryo sac in the ovule of an angiosperm involves the formation of a single functional megaspore through meiosis, which then undergoes three rounds of mitotic division to form the mature embryo sac, containing the female gamete and supporting cells.
