Question

A typical angiosperm embryo sac at maturity is

• A. 8-nucleate and 8-celled
• B. 8-nucleate and 7-celled
• C. 7-nucleate and 8-celled
• D. 7-nucleate and 7-celled

Answer 1

The Correct Option is B

The question is asking about the structure of a typical angiosperm embryo sac at maturity. Let's explore the structure in detail to understand why the answer is "8-nucleate and 7-celled".

Explanation 

The mature embryo sac of an angiosperm is an essential part of the plant's reproductive system and is involved in the development of seeds. It develops from a single megaspore through a process called megagametogenesis. Here is a step-by-step breakdown of how the embryo sac is formed and its structure at maturity:

1. Initially, a single diploid megaspore mother cell undergoes meiosis to produce four haploid megaspores.
2. Out of the four megaspores, typically only one survives, while the others degenerate. This surviving megaspore undergoes three rounds of mitotic division, resulting in eight nuclei.
3. These eight nuclei are organized into seven distinct cells inside the embryo sac:
   • Three cells at the micropylar end: These include one egg cell and two synergids, forming the egg apparatus.
   • Three antipodal cells: These are located at the chalazal end of the embryo sac.
   • One central cell: It contains two polar nuclei that are fused in many cases to form a single diploid nucleus.

Therefore, the mature embryo sac consists of a total of seven cells but contains eight nuclei (three antipodal cells, three cells of the egg apparatus, and the central cell with two nuclei).

Conclusion

Considering the above structure, the typical angiosperm embryo sac at maturity is best described as 8-nucleate and 7-celled. This matches with the correct answer given in the options.