What is mode of nutrition in sponges?

Answer 1

Sponges are porous and sea water flows in and out of sponges. The sea water carry all sorts of nutrients, like algae, bacteria and smaller organisms, which are trapped within the sponge by minute hair-like cilia. This is what gives the sponge energy. The sponge is made of uni-cellular organisms but these cannot survive alone.

The sponge is a colony of these unicellular organisms and survives as one.