In the typical monosporic (Polygonum type) development of the female gametophyte in angiosperms, which of the four megaspores remains functional?

Answer and explanation

Correct answer: D. The single chalazal megaspore, while the three micropylar megaspores degenerate

  1. Step 1: A single diploid megaspore mother cell (MMC) in the ovular nucellus undergoes meiosis to form a linear tetrad of four haploid megaspores.
  2. Step 2: In the vast majority of angiosperms (Polygonum type), the three megaspores situated toward the micropylar end degenerate and are reabsorbed.
  3. Step 3: The single megaspore situated toward the chalazal end remains functional and undergoes three successive free-nuclear mitotic divisions to form the 8-nucleate, 7-celled embryo sac.
Answer
The single chalazal megaspore, while the three micropylar megaspores degenerate
Why not the others: 'The single micropylar megaspore...' reverses the spatial polarity of functional megaspore survival; 'All four megaspores divide mitotically...' describes tetrasporic embryo sacs (e.g., Fritillaria), which are not the standard monosporic type; 'The two middle megaspores...' describes bisporic development, not the typical Polygonum type.

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