Question

List the components of the embryo sac and mention their fate on fertilization.

Answer 1

On the basis of period and site of occurrence, meiosis is of three types −

• Gametic or terminal meiosis: In gametic meiosis diploid individual forms haploid gametes by the process of meiosis. These haploid gametes fuse to form a diploid zygote. This type of meiosis can be observed in animals.
  

• Zygotic or initial meiosis: In zygotic meiosis, haploid gametes are formed by haploid individuals by the process of mitosis. The formed haploid gametes fuse to form a diploid zygote which undergoes meiosis followed by the mitotic division to form a haploid adult. This type of meiosis is found in algae, fungi etc.
  

• Sporogenetic or intermediate meiosis: In sporogenetic meiosis, diploid sporocytes undergo meiosis to form haploid spores. Haploid spores germinate to form haploid gametophyte which produces haploid gametes by mitosis. These haploid gametes fuse to form a diploid zygote. This type of meiosis is found in higher plants like gymnosperms.