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Question
With a neat, labelled diagram, describe the parts of a mature angiosperm embryo sac. Mention the role of synergids.
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Solution
After the 8-nucleate stage, cell walls are laid down leading to the organisation of the typical female gametophyte or embryo sac.
A mature embryo sac of angiosperm
Six of the eight nuclei are surrounded by cell walls and organised into cells. Three cells present towards the micropylar end grouped together, constitute the egg apparatus. The egg apperatus, in tum consists of two synergide and one egg cell. Three cells of the chalazal end are called the antipodals. The large central cell is formed by the fusion of 2-polar nuclal. Thus, a typical angiospermic embryo sac, at maturity consisis of eight nuclei and seven cells. This embryo sac is formed from, the single megaspore, so it is called monosporic embryo sac.
Role of synergids
The synergids have special cellular thickenings at the micropylar tip called filiform apparatus, which play an important role in guiding the pollen tubes into the synergid.
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