Sexual Reproduction in Flowering Plants Test - 2

• In the case of double fertilization, which occurs in angiosperms, the primary nucleus fuses with one of the nuclei of male gametes and produces zygote and secondary nucleus fuses with another nucleus of the male gametes and forms an endosperm.
• Endosperm provides nourishment for the developing embryo. The other male gamete which enters the embryo sac fuses with the haploid egg and forms the embryo.

Thus, the correct answer is option D.

• In over 80 % of the angiosperms, the female gametophyte includes seven cells, two of which are the synergid cells. Once the pollen tube enters the synergid cell, its expansion is arrested, the tip of the tube disintegrates, and two sperm cells are released.
• Synergid cells may also be linked to the discharge of the male germ unit's cells, the direction of the two sperm cells in the degenerating synergid, and the fusion of the egg and central cell with sperm cells.
• During megasporogenesis, the diploid megaspore mother cell undergoes meiosis to form four haploid megaspores. Out of these four megaspores, three degenerate and one remains functional. The functional megaspore then undergoes mitosis to form 2 daughter nuclei which further undergo two more mitotic divisions resulting in 8 nuclei, 3 of which get organized into egg apparatus comprising of an egg cell and two synergids at the micropylar end,  other 3 nuclei get organized into antipodal cells at the chalazal end and the rest 2 nuclei from the central cell.
• Since these 8 nuclei are derived from the mitotic divisions of the haploid megaspore, these are haploid and thus, the synergids are haploid cells.

Hence, Option (A) is the correct answer.

► Megapore is a haploid structure which divides and gives rise to the embryo sac which is also called female gametophyte.

► Eight-nucleate embryo sacs may be:

• Monosporic (Example: Polygonum)
• Bisporic (Example: Allium) 
• Tetrasporic (Example: Adoxa).

Hence, the correct option is B.

• 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.

In the sixteen-cell stage of the embryo in dicots, the eight protodermal cells divide further by anticlinal division to form the embryonic surface layer, while the inner eight cells divide in different planes to form the ground meristem and procambium.

Hence, the correct option is C.

Aleurone is a protein found in protein granules of maturing seeds and tubers. It also describes one of the two major cell types of the endosperm, the aleurone layer. It is the outermost layer of the endosperm.

Structure of Maize Seed:

 

Hence, the correct option is A.

• 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.

• 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).

Parthenocarpy (parthenos-virgin, karpos-fruit) is the formation of seedless fruits without fertilization. The fruits developed from unfertilized ovaries are called parthenocarpic fruits.

Fig: Parthenocarpic Fruits

Other options are incorrect because:

• In asexual reproduction, a single individual (parent) is capable of producing offspring.
• For apomixis and sexual reproduction. 

• 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.