Q: With a neat labeled diagram describe the parts of a mature angiosperm embryosac. Mention the role of synergids.
A: Embryosac or female gametophyte in many angiosperms is formed from a single functional megaspore.
This kind of development is called monosporic development.
The single megaspore divides by three nuclear (mitotic) divisions to produce 8 nuclei which become 7 celled later.
A typical angiosperm embryosac is thus 8 nucleated and 7 celled.
The eight nuclei organize into three regions: Egg apparatus, Antipodals and Central cell.
The egg apparatus is present at the micropylar end and contains one egg cell (female gamete) and two synergids with filiform apparatus.
Three antipodal cells are present at the chalazal end. These are the vegetative cells of the embryosac and degenerate before or after fertilization.
The large central cell has two polar nuclei.
Role of synergids:
The synergids guide the movement of pollen tube into them. They also direct the movement of one male gamete towards the egg cell for fertilization.