Embryo sac

Definition

The embryo sac is the female gametophyte of flowering plants, which contains the egg cell and is essential for sexual reproduction. It develops within the ovule and plays a crucial role in the processes of fertilization and seed development. The structure of the embryo sac is intricately linked to reproductive development, as it houses the necessary cells that will participate in forming the next generation of plants.

5 Must Know Facts For Your Next Test

1. The embryo sac typically contains seven cells, including one egg cell, two synergids, three antipodal cells, and one central cell with two polar nuclei.
2. It develops from a single megaspore through a process known as megagametogenesis, which involves mitotic divisions and cellular differentiation.
3. The successful fertilization of the egg cell by sperm cells occurs within the embryo sac, leading to the formation of a zygote and eventually a seed.
4. The embryo sac is crucial for double fertilization, a unique process in angiosperms where one sperm fertilizes the egg while another fuses with two polar nuclei to form triploid endosperm.
5. The arrangement and formation of the embryo sac can vary among different plant species, showcasing diverse adaptations for reproduction.

Review Questions

• Explain how the structure of the embryo sac contributes to its function in plant reproduction.
  • The structure of the embryo sac is specifically designed to facilitate its role in plant reproduction. It contains seven cells that have distinct functions; for instance, the egg cell is crucial for fertilization, while synergids help guide pollen tubes to ensure successful sperm entry. The arrangement of these cells allows for efficient interactions during fertilization and also supports double fertilization, which is essential for forming both the zygote and the nutrient-rich endosperm.
• Discuss the process of megasporogenesis and its importance in forming the embryo sac.
  • Megasporogenesis is vital because it leads to the formation of megaspores from which the embryo sac develops. This process occurs in the ovule and involves meiosis, resulting in typically four megaspores, though usually only one survives to develop into the mature embryo sac. Understanding this process highlights how integral it is to ensure that the female gametophyte is correctly formed to allow for successful fertilization and subsequent seed development.
• Evaluate how double fertilization influences seed development and plant evolution.
  • Double fertilization is a key evolutionary adaptation in flowering plants that has significant implications for seed development. In this process, one sperm fertilizes the egg cell to create a zygote while another sperm fuses with two polar nuclei to form triploid endosperm. This endosperm provides essential nourishment to the developing embryo, enhancing seed viability and success. The efficiency of this reproductive strategy has allowed angiosperms to diversify and thrive in various environments, shaping their evolution.

Related terms

Ovule:

The structure within a seed plant that develops into a seed after fertilization and contains the embryo sac.

Megasporogenesis: The process by which megaspores are produced in plants, leading to the formation of the embryo sac.

Synergids: Two specialized cells located near the egg cell in the embryo sac that play a role in guiding pollen tubes for successful fertilization.