The Nucleolus and Its Function — Reading Comprehension

Inside the nucleus of a cell, there is a small, dense structure called the nucleolus. Although it may seem like just a spot within the nucleus, the nucleolus plays a very important role in the life of a cell. It is responsible for making ribosomes, which are essential for building proteins. Proteins are needed for almost everything a cell does, from repairing damage to supporting cell growth and communication.

The nucleolus is not surrounded by a membrane like other organelles. Instead, it forms around specific regions of DNA called nucleolar organizing regions. These regions carry the instructions for making ribosomal RNA (rRNA), a key part of ribosomes. The nucleolus reads this DNA and uses it to produce rRNA, which then combines with proteins to build ribosome subunits. These subunits are later sent out of the nucleus into the cytoplasm, where they join together to form complete ribosomes.

The size and number of nucleoli in a cell can change depending on how active the cell is in making proteins. For example, cells that produce lots of proteins—like muscle cells or cells in the pancreas—usually have larger or multiple nucleoli. This shows how closely the nucleolus is linked to the cell’s activity and health.

Although small, the nucleolus is a key part of how cells grow and function. Without it, cells could not make the ribosomes needed to produce proteins, and life as we know it would not be possible.

Fun Fact: The nucleolus disappears when a cell is dividing and then reappears when the process is complete—like a temporary break during the cell's busy schedule!

Where is the nucleolus found?

What is the main function of the nucleolus?

What is produced in the nucleolus to help build ribosomes?

What do ribosomes help the cell make?

What happens to the nucleolus during cell division?

Why might a muscle cell have a large nucleolus?

What is the main idea of the passage?

If a cell couldn’t make rRNA, what might happen?