Explain why sexual reproduction in angiosperms is said to take place through double fertilization and triple fusion. Also draw a labelled diagram of embryo sac to explain the phenomena.

Explanation

Two male gamets are discharged into embryo sac of ovule . One male gamete fuses with egg to form zygote (2n). Second male gamete fuses with diploid secondary nucleus to form primary endosperm nucleus ( 3n) . Because both male gametes are involved the process is called double fertilization . Zygote forms embryo (2n) and primary endosperm nucleus form endosperm (3n) .