Final answer:
The nucleus is a structure that is unique to eukaryotic cells. It is a membrane-bound organelle that contains the cell's DNA and controls its functions.
Step-by-step explanation:
The nucleus is a structure that is unique to eukaryotic cells. It is a membrane-bound organelle that contains the cell's DNA and controls its functions. The nucleus is not present in prokaryotic cells, which are simpler and do not have membrane-bound organelles.
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