Simulation · Biology · Class 12
Building the embryo sac
"Building the embryo sac" is a free, interactive Class 12 Biology simulation for NEET, built on the lesson "The embryo sac" in Sexual Reproduction in Flowering Plants. Move the slider one step at a time. Watch the number of nuclei, and notice when (and only when) walls appear. Monosporic development: 1 functional megaspore, 3 free-nuclear mitoses, then walls. The mature embryo sac is 7-celled and 8-nucleate, with the egg apparatus at the micropylar end.
From the lesson The embryo sac in Sexual Reproduction in Flowering Plants. Change the values and watch what happens.
Building the embryo sacBiology · Class 12
The idea behind it
NCERT §1.2.2
- In most flowering plants only one of the four megaspores is functional; the other three degenerate. Forming the embryo sac from a single megaspore is called monosporic development.
- The functional megaspore's nucleus divides by mitosis into two nuclei that move to opposite poles (2-nucleate embryo sac). Two more mitotic divisions give the 4-nucleate and then the 8-nucleate stage.
- These three divisions are strictly free-nuclear: the nuclei divide without walls forming right after. Walls are laid down only after the 8-nucleate stage, organising the mature embryo sac.
- Six nuclei are walled off into cells. At the micropylar end, three cells form the egg apparatus: two synergids and one egg cell. At the chalazal end are three antipodal cells.
- The remaining two nuclei, the polar nuclei, lie in the large central cell just below the egg apparatus.
- Synergids carry special thickenings at their micropylar tip, the filiform apparatus, which guides the pollen tube into a synergid.
- So the typical mature angiosperm embryo sac is 8-nucleate but 7-celled: 3 antipodals + 2 synergids + 1 egg + 1 central cell with 2 polar nuclei.
Questions
2 answers
- What does the "Building the embryo sac" simulation show?
- Move the slider one step at a time. Watch the number of nuclei, and notice when (and only when) walls appear.
- Is this simulation free?
- Yes. It is free and runs in the browser on a phone or a laptop. It belongs to the lesson "The embryo sac" in Sexual Reproduction in Flowering Plants (Class 12 Biology).
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