Q. Do algae reproduce asexually or sexually?
There are algae that reproduce asexually, There are algae that reproduce sexually and. In unicellular algae reproduction is usually asexual by binary division. In pluricellular algae asexual reproduction can take place by fragmentation or by sporulation.
In sexual reproduction of algae, pluricellular or uni, there is fusion of gametes (syngamy). There are algae in which all cells can become gametes and there are algae in which only some cells can play that role, some species may present alternation of generations forming sporophytes and gametophytes with different ploidies.