Question

Why is embryo sac of angiosperm haploid

Answer 1

In embryo sac, each cell contain only a single set of chromosome, hence is haploid. Thus, the ploidy of embryo sac is haploid (n). 

When pollen grains reaches stigma of flower, they give rise to a pollen tube containing two male gametes. 

Diploid zygote - It is the fusion of one of the male gamete (n) of pollen tube with the egg cell (n) and leads to the formation of a diploid zygote (n+n=2n). This process of fertilization is called as syngamy.

*where n = haploid number of chromosomes.

Triploid endosperm is the endosperm of seed having 3n chromosomes (where n is the haploid no.of chromosomes). During triple fusion- one of the male gamete (n) of pollen tube fuses with the two polar nuclei (2n) which lead to the formation of central cell (n+2n= 3n number of chromosomes) .This central cell finally develops into a triploid endosperm.