Question

The endosperm in angiosperm develops from:
A. Zygote
B. Secondary nucleus
C. Chalazal polar nucleus
D. Micropylar polar nucleus

Answer 1

Hint: Endosperm development begins with forming a triploid cell (3n) in the embryo sac. The primary endosperm nucleus (PEN) and a triploid cell are formed when the second male gamete fuses with the diploid secondary nucleus (formed by two polar nuclei). The technique is known as triple fusion.


Step by step solution:
A diploid nucleus generated by the merger of two polar nuclei is the secondary nucleus. It's also referred to as the primary endosperm nucleus.
The pollen tube releases two male gametes into the cytoplasm of the synergid, which fuses with two nuclei present in the synergid upon entering one of them.
One of the pollen grains' male gametes proceeds toward the egg cell and unites with its nucleus, completing the syngamy. This results in the creation of a diploid cell, known as a zygote.
The second male gamete proceeds to the central cell's two polar nuclei and combines with them to form the secondary nucleus or triploid primary endosperm nucleus.
Triple fusion refers to fertilizations that entail the merging of three haploid nuclei.
Both forms of fusions, syngamy, and triple fusion occur in an embryo sac, resulting in double fertilization, a mechanism unique to flowering plants.
After fertilization, the central cell becomes the primary endosperm cell (PEC) and grows into the endosperm that nourishes the embryo whilst the zygote develops into an embryo.
Additional information:
Endosperm development can be classified into three types:
Nuclear endosperm production is characterized by recurrent free-nuclear divisions; if a cell wall is created, it will occur after free-nuclear divisions. Commonly known as liquid endosperm. Coconut water is one example.
Cellular endosperm development occurs when the establishment of a cell wall coincides with nuclear divisions. Coconut meat is made up of cellular endosperm. Acoraceae develop cellular endosperm, whereas other monocots are helobial.
Helobial endosperm formation is characterized by the production of a cell wall between the first two nuclei, after which one half grows endosperm along the cellular pattern and the other half along the nuclear pattern.

So, option B is correct.
Note: After complete development, the embryo sac has a distinct cell distribution, with one end known as the micropylar end and the other as the chalazal end. The egg apparatus is formed by three cells packed together at the micropylar end (2 synergids and an egg cell).