Question

Plasmogamy is a fusion of
A. Two haploid cells including their nuclei
B. Two haploid cells without nuclear fusion
C. Sperm and egg
D. Sperm and two polar nuclei

Answer 1

Hint: Fusion of two cells either gives an uninucleated cell or can give a binucleate cell depending on which cell is conducting it and how. Haploidy will convert into diploidy if there is binucleate cell formation after the fusion of the protoplast also. Plasmogamy and karyogamy are such processes.

Complete answer:
What is plasmogamy?
When there is a fusion of two protoplasts and the two nuclei come together in the same protoplasm making a binucleate cell, it is called plasmogamy. The cell pair is called dikaryon. In lower fungi, it happens followed by karyogamy. In the higher fungi, both processes take place at a lap.

Let us see the options in the question.
> Option A: Two haploid cells including their nuclei: This tells that there is the fusion of both cytoplasm and the nuclei to form a single diploid nucleus. But as we know in plasmogamy only the protoplast fuse. So this is incorrect.

> Option B: Two haploid cells without nuclear fusion: the fusion of two cells takes place without the fusion of their nuclei, we get a binucleated cell.

> Option C: Sperm and egg: Sperm and eggs are haploid cells which fuse to form the diploid cell having single protoplasm and single nuclei. So this option is incorrect.

> Option D: Sperm and two polar nuclei: Sperm being the haploid when fuses with two polar nuclei will form a triploid. The protoplast will fuse forming three nuclei. So the option is incorrect also in the regard that plasmogamy means fusion of two haploid cells not diploid or binucleate cells.

Hence, The correct answer is option (B).

Note: Firstly plasmogamy includes fusion of haploid but after it, there is the formation of a diploid cell when karyogamy takes place. Plasmogamy is an intermediate step in the fusion of two cells. It remains for a short time. But in some fungi, the process is arrested at the plasmogamy stage.