Question

What is the port of the entry of pollen tube into an embryo sac of capsella.
A) Oosphere
B) One of the synergids
C) One of the antipodal cell
D) None of the above

Answer 1

Hint: Capsella is a genus of flowering plants in the mustard family or Brassicaceae. Capsella is angiosperm because of the presence of covered seeds. Angiosperms have a type of fertilization mechanism called double fertilization. This process involves the joining of a single female gametophyte with two male gametes.

Complete answer:
The double fertilization in angiosperms begins when a pollen grain adheres to the stigma of the carpel which is the female reproductive structure of a flower. After pollen is deposited on the stigma, it starts germinating and grows through the style to reach the ovule. The pollen or the microspores contain two cells: the generative cell and the pollen tube cell. The pollen tube cell develops into a pollen tube. Through the pollen tube, the generative cell travels.
The germination of the pollen tube requires oxygen, water and certain chemical signals. The pollen tube’s growth is supported by the tissues of the style, as it travels through the style to reach the embryo sac. The pollen tube enters into the embryo sac only through the micropylar end either passing in between synergid and egg cell. Before the entry of the pollen tube into the embryo sac, one of the synergids begins to degenerate. This cell acts as a site for the entry of pollen tubes. The generative cell splits into two cells, it divides to form two sperm cells. Synergids secretes chemical; which guide the pollen tube. Synergids are present in the embryo sac, and it enters the ovule sac through the micropyle.

Hence, the correct answer is option (B).

Note: The two fertilization events in angiosperms are known as double fertilization. After the completion of fertilization, no other sperm can enter the ovule. The fertilized ovule forms seed and the tissues of the ovary become the fruit, usually enveloping the seed.