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प्रश्न
With a neat, labelled diagram, describe the parts of a mature angiosperm embryo sac. Mention the role of synergids.
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उत्तर
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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संबंधित प्रश्न
From among the sets of terms given below, identify those that are associated with the gynoecium.
From the statements given below choose the option that are true for a typical female gametophyte of a flowering plant.
- It is 8-nucleate and 7-celled at maturity
- It is free-nuclear during the development
- It is situated inside the integument but outside the nucellus
- It has an egg apparatus situated at the chalazal end
In an embryo sac, the cells that degenerate after fertilisation are ______.
Draw the diagram of a mature embryo sac and show its 8-nucleate, 7-celled nature. Show the following parts: antipodals, synergids, egg, central cell, polar nuclei.
Embryo sacs of some apomictic species appear normal but contain diploid cells. Suggest a suitable explanation for the condition.
Draw a diagram of the mature embryo sac of an angiospermic ovule and label any four parts in it.
During the development of the female gametophyte, the functional megaspore undergoes mitotic divisions without immediate cell wall formation. What are these divisions called?
Which cells or cell group at the micropylar end of the mature embryo sac constitute the egg apparatus?
The central cell of the mature embryo sac contains two polar nuclei. What is the ploidy level of the central cell after the two polar nuclei fuse?
How many nuclei contribute to the formation of the endosperm, and what is the resulting ploidy level of the endosperm?
The mature embryo sac is described as monosporic and of the Polygonum type. What does the term monosporic indicate about the origin of the embryo sac?
Based on the cell distribution table, which cell or group of cells contributes a haploid gamete nucleus during double fertilization?
What is the total number of haploid nuclei present in the 8-nucleate stage of the developing female gametophyte before cell walls are formed?
How many mitotic divisions are required to convert the haploid functional megaspore into the 8-nucleate stage?
In the mature embryo sac, which structure contains the filiform apparatus that aids in guiding the pollen tube?
