Final answer:
The nucleus is a cell organelle that houses DNA and directs the synthesis of ribosomes and proteins. It is surrounded by the nuclear envelope and contains nucleoli.
Step-by-step explanation:
The nucleus is a cell organelle that houses the cell's DNA and directs the synthesis of ribosomes and proteins. It is surrounded by a double membrane called the nuclear envelope, which has protein-lined pores that allow materials to move in and out of the nucleus. The nucleus contains one or more nucleoli, which are condensed regions where ribosomes are formed.