Answer:
The organelle that is not surrounded by a membrane but sits in the nucleus is called the nucleolus.
Step-by-step explanation:
The organelle that is not surrounded by a membrane but sits in the nucleus is called the nucleolus. It is a small, dense structure that is responsible for producing ribosomes, which are essential for protein synthesis. Despite not being surrounded by a membrane, the nucleolus is separated from the rest of the nucleus by a distinct boundary, known as the nucleolus organizer region. This region contains specific genes that are involved in the production of ribosomal RNA, which is a key component of the ribosomes. The nucleolus also plays a role in regulating cell growth and proliferation.