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What are Prokaryotic Cells? — Reading Comprehension

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MS-LS1-1
MS-LS1-2

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This NGSS-aligned science reading passage explains prokaryotic cells, the simplest type of cells found in single-celled organisms like bacteria and archaea. Supporting standard MS-LS1-1, the passage describes how prokaryotic cells lack a nucleus and organelles, but still perform all life functions. Students learn key vocabulary such as 'cytoplasm,' 'DNA,' and 'flagella,' and explore how these cells help in digestion, waste breakdown, and survival in extreme environments. Designed for middle school readers, this engaging passage supports comprehension of core life science concepts aligned to the Next Generation Science Standards.

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"Average prokaryote cell- en" by Mariana Ruiz Villarreal, LadyofHats / Wikimedia Commons.

All living things are made of cells, but not all cells are the same. Scientists divide cells into two main types: prokaryotic cells and eukaryotic cells. The simpler of the two is the prokaryotic cell, which is found in single-celled organisms like bacteria and archaea.

Prokaryotic cells do not have a nucleus or other membrane-bound organelles. Instead of having their DNA stored in a nucleus, their genetic material floats freely in the cytoplasm, the jelly-like fluid inside the cell. Although they are small and simple, prokaryotic cells can carry out all the basic functions of life, such as growing, reproducing, and responding to the environment.

These cells usually have a cell wall, a cell membrane, and sometimes tiny hair-like structures called flagella or pili that help them move or attach to surfaces. Since they don’t have compartments like mitochondria or chloroplasts, all their functions happen directly in the cytoplasm or along the cell membrane.

Prokaryotic cells are believed to be the first type of life to appear on Earth—over 3.5 billion years ago. They are very adaptable and can live in extreme environments like hot springs, salty lakes, or deep ocean vents. Even though they are small, they play big roles in ecosystems, such as helping us digest food or breaking down waste in the environment.

Fun Fact: The bacteria in your body outnumber your own cells—by nearly 10 to 1!

What type of organisms have prokaryotic cells?

Humans and animalsTrees and flowersBacteria and archaeaFungi and protists

What do prokaryotic cells lack?

A cell wallCytoplasmA nucleus and organellesDNA

Where is the DNA found in a prokaryotic cell?

Inside the nucleusIn the mitochondriaFloating in the cytoplasmInside the cell wall

What part of the cell helps it move or attach to things?

RibosomeFlagella or piliNucleusChloroplast

How old are prokaryotic cells estimated to be?

100 years5 million years5 billion years350 years

What is one reason prokaryotic cells are important?

They store oxygenThey create rocksThey help break down wasteThey block viruses

What is the main idea of the passage?

Prokaryotic cells are found in plantsProkaryotic cells are complex and hugeProkaryotic cells are simple cells found in single-celled organismsProkaryotic cells only exist in the ocean

If prokaryotic cells didn’t exist, what might happen?

Food would taste betterWaste might not break down properlyPlants wouldn’t need waterAll animals would have shells