The nucleolus is a small, round structure found inside the nucleus of a cell. It plays a crucial role in producing ribosomes, which are essential for protein synthesis. Ribosomes are like tiny factories that help build proteins, the building blocks of life. The nucleolus is made up of RNA and proteins, and it becomes more active when a cell needs to produce more proteins. When a cell is not dividing, the nucleolus is usually visible under a microscope. It can change in size depending on the cell's activity level. In summary, the nucleolus is vital for cell function, helping to ensure that proteins are made efficiently.