Test: Double Fertilisation - NEET MCQ

• The fusion of one male gamete with the egg cell is called Syngamy or true fertilization while the fusion of second male gamete with two polar nuclei is called triple fusion.
• Syngamy along with the triple fusion is called double fertilization. Double fertilization is a characteristic feature of flowering plants or angiosperms.   

Hence, the correct option is B.
Topic in NCERT: DOUBLE FERTILISATION
Line in NCERT: "One of the male gametes moves towards the egg cell and fuses with its nucleus thus completing the syngamy."

Double fertilisation is a unique process observed in angiosperms (flowering plants). It involves the fusion of the male and female gametes, forming two distinct products - the zygote and the primary endosperm nucleus (PEN).
Formation of the Zygote:

• One of the two male gametes fuses with the egg cell to form the zygote. This process is known as syngamy.

Formation of the Primary Endosperm Nucleus:

• The other male gamete fuses with the two polar nuclei (found within the central cell of the ovule) to form the primary endosperm nucleus. This process is known as triple fusion because it involves the fusion of three nuclei.

Central Cell After Triple Fusion:

• After triple fusion, the central cell becomes the primary endosperm cell (PEC), which contains the primary endosperm nucleus (PEN).

Therefore, the correct answer is b. Primary Endosperm Nucleus (PEN). This is the central cell after triple fusion in double fertilisation.
Topic in NCERT: POST-FERTILISATION: STRUCTURES AND EVENTS
Line in NCERT: "The central cell after triple fusion becomes the primary endosperm cell (PEC) and develops into the endosperm while the zygote develops into an embryo."

Here's the explanation in detail:
-  A are degenerating synergids, which are haploid (n) 
- B is diploid (2n) as it represents the zygote formed by the fusion of male and female gametes.
- C  is triploid (3n) as it represents endosperm formed by the fusion of two polar nuclei and a sperm cell.
- D are degenerating antipodal cells, which are haploid (n) 
This analysis validates both Statement I and Statement II ARE INCORRECT
Diagram from NCERT: 

Topic in NCERT: POST-FERTILISATION: STRUCTURES AND EVENTS
Line in NCERT: "The large central cell, as mentioned earlier, has two polar nuclei." "The zygote develops into an embryo." "Degenerating synergids" "Degenerating antipodal cells"

• The pollen grains germinate on the stigma and the resulting pollen tubes grow through the tissues of stigma and style and reach the ovule.
• The pollen tubes enter the embryo-sac where two male gametes are discharged. One of the male gametes fuses with the egg cell (syngamy) and forms a diploid zygote. The other male gamete fuses with the diploid secondary nucleus to four primary endosperm nucleus (PEN), which is triploid in nature.
• Since, two types of fusion. Syngamy and triple fusion takes place in the embryo sac, the process is known as double fertilisation. 

Topic in NCERT: DOUBLE FERTILISATION
Line in NCERT: "One of the male gametes moves towards the egg cell and fuses with its nucleus thus completing the syngamy. 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)."

In double fertilisation, after the pollen tube enters the synergid, the two male gametes are released. One fuses with the egg cell to form the diploid zygote, and the other fuses with the two polar nuclei to form the triploid primary endosperm nucleus (PEN). The zygote develops into the embryo, and the primary endosperm nucleus forms the endosperm. This process is termed double fertilisation, which is unique to flowering plants.

Topic in NCERT: DOUBLE FERTILISATION

Line in NCERT: "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)."