Embryo sac is monosporic when it develops from

Options

A. one of the four megaspores of a megaspore mother cell
B. three megaspores of a megaspore tetrad
C. wo functional megaspores
D. the megaspore mother cell where meiosis has occurred but cytokinesis does not take place

Answer

### Step-by-Step Solution:

1. **Understanding the Embryo Sac**: The embryo sac is a structure that develops within the ovule of flowering plants and is crucial for reproduction. It contains the female gametes.

2. **Definition of Monosporic**: A monosporic embryo sac develops from a single functional megaspore. This means that out of the four megaspores produced after meiosis, only one will develop into the embryo sac.

3. **Formation of Megaspores**: The process begins with a megaspore mother cell (megasporangium) undergoing meiosis. This meiotic division results in four haploid megaspores.

4. **Selection of Functional Megaspore**: Out of the four megaspores formed, typically only one megaspore survives and becomes functional. The other three megaspores degenerate.

5. **Development of the Embryo Sac**: The functional megaspore then undergoes mitotic divisions to form the embryo sac. This structure will eventually contain the egg cell and other cells necessary for fertilization.

6. **Conclusion**: Therefore, the embryo sac is considered monosporic when it develops from one of the four megaspores produced by the megaspore mother cell.

7. **Correct Answer**: The correct option is **A**: one of the four megaspores of a megaspore mother cell.