In the diagram given below, show the path of a pollen tube from the pollen on the stigma into the embryo sac. Name the components of egg apparatus.
Following compatible pollination, the pollen grain germinates on the stigma to produce a pollen tube through one of the germ pores. The contents of the pollen grain ( 2 mole nuclei) move into the pollen tube. Pollen tube grows through the tissues of the stigma and reaches the ovary.
After reaching the ovary, pollen tube, enters the ovule through the micropyle and then enters the embryo sac by passing into one of the synergids through the filiform apparatus. It leads to the degeneration of that synergid.
The pollen tube breaks to release its contents (2 male nuclei). Out of the two male gametes one fuses with egg and the other fuses with central cell and fertilise.
$$ \text { Longitudinal section of a flower showing path of pollen tube growth } $$
The component cells of the egg-apparatus in an embryo sac include, two synergids, one egg cell and the filiform apparatus.
$$ \text { A diagrammatic representation of the mature embryo sac } $$
Name the parts of pistil which develop into fruit and seeds.
Pistil is the female reproductive organ that receives pollen to fertilise the egg located in ovary. A pistil has three parts, i.e., stigma (receives pollen), which grows down through style to ovary. Ovary contains ovules, which contain an egg. The ovary develops into the fruit and ovule develops into a seeds.
In case of polyembryony, if an embryo develops from the synergid and another from the nucellus which is haploid and which is diploid?
Embryo developed from the synergid is haploid as the ploidy of the synergid is haploid. Embryo developed from the nucellus is diploid as the ploidy of the nucellus is diploid.
Can an unfertilised, apomictic embryo sac give rise to a diploid embryo? If yes, then how?
Yes, if megaspore develops into embryo sac without meiotic division egg will be diploid. Diploid egg develops into embryo by mitotic divisions.
Which are the three cells found in a pollen grain when it is shed at the three celled stage?
In over 60\% of angiosperms, pollen grains are shed at the two cell further stage (vegetative cell and generative cell). In the remaining species, the generative cell divides mitotically to give rise to the two male gametes before pollen grains are shed at the (three-celled stage (are vegetative cell and two male gametes).