A labelled diagram of a mature embryo sac shows: at the micropylar end, a cell P flanked by two cells Q that bear finger-like thickenings at their tips; at the chalazal end, three cells R; and in the middle, a large cell containing two nuclei S. During double fertilisation, the two male gametes fuse respectively with which labelled parts?
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One male gamete fuses with the egg cell (syngamy) to form the diploid zygote; the other fuses with the two polar nuclei of the central cell (triple fusion) to form the triploid primary endosperm nucleus. P is the egg, Q the synergids, R the antipodals and S the polar nuclei.
- A.
Q are synergids; the pollen tube releases gametes into a synergid but the gamete fuses with the egg.
- C.
R are antipodal cells; the second male gamete fuses with the polar nuclei.
- D.
The zygote forms from the egg (P), not the polar nuclei.
NCERT: Class 12 Biology, Chapter 1, 1.3