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The Nucleolus and Its Function — Reading Comprehension

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MS-LS1-1
MS-LS1-2

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This NGSS-aligned reading passage focuses on the nucleolus, a key structure inside the cell’s nucleus responsible for making ribosomes. Targeted to middle school students, the passage explains how the nucleolus produces ribosomal RNA (rRNA), which is essential for building ribosomes that make proteins. It also discusses why the size of the nucleolus varies between cell types and what happens to it during cell division. This reading supports NGSS standard MS-LS1-1 and helps students understand the relationship between structure and function in living cells. Designed for use in science classrooms to reinforce reading comprehension and life science content.

CONTENT PREVIEW

"Diagram human cell nucleus" by Mariana Ruiz LadyofHats / Wikimedia Commons.

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?

In the cytoplasmInside the ribosomeInside the nucleusOn the cell membrane

What is the main function of the nucleolus?

Store DNAMake energyMake ribosomesControl cell division

What is produced in the nucleolus to help build ribosomes?

MitochondriaRibosomal RNA (rRNA)CytoplasmDNA strands

What do ribosomes help the cell make?

SugarsProteinsWaterMembranes

What happens to the nucleolus during cell division?

It gets largerIt disappears temporarilyIt moves to the cell membraneIt turns into ribosomes

Why might a muscle cell have a large nucleolus?

It divides quicklyIt needs to store energyIt makes a lot of proteinsIt digests food

What is the main idea of the passage?

The nucleolus controls the whole cellThe nucleolus helps cells reproduceThe nucleolus builds ribosomes needed for protein productionCells cannot survive without a membrane

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

It would grow fasterIt would stop producing proteinsIt would store more DNAIt would make more mitochondria