Organism that can only exist as a group of cells

I'm guessing you want to know what it is called, so I guess I'll just guess an answer. I think the answer is 'multicellular'. Multicellular basically means a group of cells. 'Multi' means many and 'cellular' basically means cells. So I guess that total amount means 'a group of cells'.
I don't know what else you want, so just good luck and hope I helped. :)
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The basic building blocks of dna and rna are nucleotides