Q.

In Spirogyra, asexual reproduction takes place by:

1 breaking up of filaments into smaller bits.  
2 division of a cell into two cells.  
3 division of a cell into many cells.  
4 formation of young cells from older cells.  

Ans.

(1)

In Spirogyra, asexual reproduction takes place by fragmentation, i.e., the organism simply breaks up into smaller pieces upon maturation. Each piece grows into new individual without forming any gametes.