Question

PEN stands for
(a) Primary endosperm nourishment
(b) Primary endosperm nucleus
(c) Primary embryo nourishment
(d) Poly embryo nourishment

Answer 1

Hint: The triploid cell formed after the fusion of remaining male gametes after fertilization with the central cell. It involves the fusion of three haploid nuclei resulting in triple fusion.

Complete answer:
PEN stands for the primary endosperm nucleus. In double fertilization of gymnosperms, after fertilization, a diploid zygote is formed and the other male gametes move towards the two polar nuclei located in the central cell. These cells fuse together resulting in a triploid primary endosperm nucleus(PEN).

Additional information:
- The pollen tube after entering into the synergids, it bursts and releases two male gametes into the cytoplasm of the synergid. One of the male gametes moves toward the egg cell. The nucleus of the male gamete fuses with the nucleus thus completing fertilization. It is also called syngamy.

- A diploid zygote is formed after fertilization. The other male gametes move towards the two polar nuclei located in the central cell and fuse with them to produce a triploid primary endosperm nucleus (PEN) that involves the fusion of three haploid nuclei. This is called triple fertilization.
- This is called double fertilization because in the embryo sac, two types of fusions, fertilization, and triple fusion, takes place.
- One of the unique features of flowering plants is double fertilization.
So, the correct answer is ‘(b) Primary endosperm nucleus’.

Note:
- Primary endosperm cell (PEC) is formed from the central cell after the double fertilization and later it develops into endosperm, and the embryo is developed from the zygote.
- Endosperm formed after double fertilization helps in the development of the embryo by providing food for the developing embryo as it is used to store food.