Sexual reproduction in Spirogyra is an advanced feature because it shows (a) different sizes of motile sex organs (b) same size of motile sex organs (c) morphologically different sex organs (d) physiologically differentiated sex organs.
Option D Spirogyra is a freshwater green alga which belongs to Class Chlorophyceae. The sexual reproduction in Spirogyra is called conjugation. It involves the fusion of two morphologically identical but physiologically dissimilar nonciliated gametes. For development of gametes, some of the cells start to act like male and female gametangia in which the cell contents become separated from the cell wall, shrink and ultimately forms gametes. The fusion of these gametes takes place by scalariform conjugation or lateral conjugation
