Arrange the given events of double fertilization in correct sequence.
A. Fusion of second male gamete with two polar nuclei
B. Fusion of first male gamete with egg cell
C. Formation of primary endosperm nucleus
D. Formation of zygote
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → B, D, A, C
B. Fusion of first male gamete with egg cell — first. The pollen tube releases two male gametes into a synergid. One male gamete moves to the egg cell and fuses with its nucleus. This fusion is syngamy.
D. Formation of zygote — second. Syngamy produces a diploid cell, the zygote. The zygote later develops into the embryo.
A. Fusion of second male gamete with two polar nuclei — third. The other male gamete moves to the two polar nuclei in the central cell and fuses with them. Three haploid nuclei fuse here, so this is called triple fusion.
C. Formation of primary endosperm nucleus — last. Triple fusion produces the triploid primary endosperm nucleus (PEN), which later forms the endosperm.
Syngamy and triple fusion together are called double fertilisation, an event found only in flowering plants.
NCERT Extract:
Double Fertilisation – “After entering one of the synergids, the pollen tube releases the two male gametes into the cytoplasm of the synergid. One of the male gametes moves towards the egg cell and fuses with its nucleus thus completing the syngamy. This results in the formation of a diploid cell, the zygote. The other male gamete moves towards the two polar nuclei located in the central cell and fuses with them to produce a triploid primary endosperm nucleus (PEN) (Figure 1.13a). As this involves the fusion of three haploid nuclei it is termed triple fusion. Since two types of fusions, syngamy and triple fusion take place in an embryo sac the phenomenon is termed double fertilisation, an event unique to flowering plants.”
