Question

Why (and how) does the male gamete cell fuses with the female gamete cell of a plant?

Is it because of the reason that both of the gametes have different charges and hence attract each other or is it like that they form a (Chemistry) bond?

Answer 1

However, in flowering plants, the gametes of both sexes lack motility. Two sperm cells (male gametes) that are contained in a pollen grain are recessively delivered via pollen tube elongation. After the pollen tube bursts, sperm cells are released toward the egg and central cells (female gametes) within an ovule. The precise mechanism of sperm cell movement after the pollen tube bursts remains unknown. Ultimately, one sperm cell fuses with the egg cell and the other one fuses with the central cell, producing an embryo and an endosperm, respectively.

The fact that each morphologically identical sperm cell precisely recognizes its fusion partner strongly suggests that an accurate gamete interaction system exists in flowering plants.
The compound was collected from laboratory cultures of fertile female gametophytes of the cosmopolitan brown alga Ectocarpus siliculosus. Soon after release, the originally motile female microgametes begin to settle on a surface and start to secrete a chemical signal. The biological function of this pheromone is the improvement of mating efficiency by attraction of the flagellated, motile males. The chemical structure of the signal compound was established as 6-(1Z)-(butenyl)cyclohepta-1,4-diene (ectocarpene )