The nucleus of a functional megaspore divides by mitosis three times in a row…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
The nucleus of a functional megaspore divides by mitosis three times in a row. Every nucleus divides in each round.
- How many nuclei are there after two rounds?
- How many divisions of nuclei take place in all, from the first nucleus to the 8-nucleate stage?
- How many cells are in the mature embryo sac?
Need a reminder? The key ideaShow
An ovule has one megaspore mother cell (MMC), which is diploid. The MMC divides by meiosis into four haploid megaspores. In most plants, one is functional and three degenerate. The functional megaspore divides by mitosis three times, with no walls, to make 8 nuclei. The mature embryo sac has 7 cells: the egg, 2 synergids, 3 antipodals and the central cell with 2 polar nuclei.
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Given. Three rounds of mitosis, starting with nucleus.
Plan. Double the nuclei in each round. Count the divisions in each round.
Step 1. After two rounds. , so nuclei.
Step 2. The divisions. Round one has division, round two has , and round three has . That is divisions.
Step 3. The cells. After the 8-nucleate stage, walls form. There are cells at the micropylar end, at the chalazal end and the central cell, so cells.
Answer: nuclei; divisions; cells.
Check. Each division adds one nucleus. From to nuclei needs divisions.
Watch out. Three rounds are not three divisions. There are seven divisions of single nuclei.
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