sentence2_structure: Prokaryotes<>are<>unicellular organisms that lack organelles$$$unicellular organisms<>lack<>organelles surrounded by membranes$$$organelles<>surrounded<>
sentence1: Prokaryotes lack a nucleus and other membrane-bound organelles, although they have circular DNA and ribosomes.
sentence2: Prokaryotes are unicellular organisms that lack organelles surrounded by membranes.
question: Prokaryotes are unicellular organisms that lack organelles surrounded by what?