Q.62 Which one of the following statements is CORRECT with respect to endosperm
development? It originates
(A) from the fusion product of three haploid nuclei – one from male gametophyte and two
from the female gametophyte
(B) from the fusion product of three haploid nuclei – two from male gametophyte and one
from the female gametophyte
(C) from the fusion product of two haploid nuclei – one from male gametophyte and one
from the female gametophyte
(D) by a phenomenon called apomixis
The correct answer is (A).
Option Analysis
Endosperm develops in angiosperms via double fertilization, where one sperm fuses with the egg to form the zygote, and the second sperm fuses with two polar nuclei in the central cell to form the triploid primary endosperm nucleus (PEN).
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(A) Correct: The PEN arises from one haploid nucleus from the male gametophyte (second sperm) and two haploid polar nuclei from the female gametophyte (embryo sac central cell). All are haploid, fusing to 3n.
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(B) Incorrect: Male gametophyte contributes only one sperm for endosperm; the other forms the zygote. Two from male would imply different fusion.
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(C) Incorrect: This describes syngamy (sperm + egg), forming diploid zygote/embryo, not triploid endosperm.
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(D) Incorrect: Apomixis is asexual seed formation without fertilization; endosperm typically requires fertilization, though pseudogamous forms exist.
Endosperm development fusion three haploid nuclei defines a core process in angiosperm reproduction, ensuring nutrient supply for embryos via triploid tissue.
Double Fertilization Mechanism
Pollen tube delivers two haploid sperm cells from the male gametophyte. One fuses with the egg (syngamy, 2n zygote); the second undergoes triple fusion with two haploid polar nuclei from the female gametophyte’s central cell, forming 3n PEN. This precedes embryo growth for nourishment.
Nuclei Origins
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Male gametophyte: Haploid generative cell divides into two sperm.
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Female gametophyte: Embryo sac has 7 cells/8 nuclei; two polar nuclei (haploid) in central cell.
PEN divides mitotically, developing into cellular, nuclear, or helobial endosperm types.
Exam Relevance
For CSIR NET, recognize triple fusion’s role; apomixis bypasses it but is not standard.
