Test: Double Fertilisation - NEET MCQ

∗ In the most common type of endosperm development, the PEN undergoes successive nuclear division to give rise to free nuclei.
∗ Embryo develops at the micropylar end of the embryo sac where zygote is situated.

Line in NCERT: "In the most common type of endosperm development, the PEN undergoes successive nuclear divisions to give rise to free nuclei."

• Double fertilization occurs only in angiosperms.
• The female gametophyte in angiosperms abruptly stop their growth at 8 nucleate stages.

- Statement I: It represents mature embryosac or the female gametophyte in an angiosperm.
- Statement IV: D is the polar nuclei and E is the central cell.
- Statement V: F is the egg cell.

These statements are correct. The diagram shows the structure of an angiosperm's female gametophyte.

D represents the polar nuclei,

E the central cell, and

F the egg cell within the embryo sac.

These structures are vital for the process of fertilization in plants.

Line in NCERT: "The mature embryo sac is 7-celled and 8-nucleate. At the micropylar end is the egg apparatus consisting of two synergids and an egg cell. At the chalazal end are three antipodals. At the centre is a large central cell with two polar nuclei."

• Synergids are haploid in nature. This means they contain one complete set of chromosomes. They are formed as a result of meiosis, a type of cell division that reduces the number of chromosomes in parent cells to half, resulting in four daughter cells, each with half the number of chromosomes of the parent cell.
• Role in Fertilization: The primary role of synergids is to help in the process of fertilization. One of the two synergids will fuse with a pollen grain (male gamete) to form the zygote, while the other synergid degenerates. The haploid nature of synergids ensures that the resulting zygote, formed by the fusion of male and female gametes, is diploid, containing two sets of chromosomes.

Hence, Option (A) is the correct answer.

Line in NCERT: "After entering one of the synergids, the pollen tube releases the two male gametes into the cytoplasm of the synergid."

• 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.

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.

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

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. 
  
• Hence, the correct option is A.

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)."

• Endosperm is formed during double fertilization.
• It is triploid because it is formed when one of the two sperm that is haploid enters inside the embryo sac & fuses with two polar nuclei (each polar nuclei is haploid).
• So the endosperm formed is triploid.

Hence, the correct option is B.

Line in NCERT: "The primary endosperm cell divides repeatedly and forms a triploid endosperm tissue."

• Endosperm can be classified into two types according on how it is consumed during development: endospermic and non-endospermic.
• If the endosperm is consumed by the growing embryo, it is said to be non-endospermic.
• In some plants, the endosperm is completely absorbed by the embryo, some of the examples are peas, beans, and green gram, in this type of food is stored in dicot seeds.
• Whereas in some dicots, food is stored in endosperm examples are castor, maize, etc.
• In the case of coconut, the endosperm is present in the liquid form and it is stored.

Hence, The correct answer is option (C).

Line in NCERT: "Endosperm may either be completely consumed by the developing embryo (e.g., pea, groundnut, beans) before seed maturation or it may persist in the mature seed (e.g. castor and coconut) and be used up during seed germination."