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Antonie van Leeuwenhoek and the Discovery of Animalcules — Reading Comprehension

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This NGSS-aligned science passage explores the groundbreaking work of Antonie van Leeuwenhoek, a pioneer in microscopic discovery. Aimed at middle school students and supporting standard MS-LS1-1, the passage explains how van Leeuwenhoek used handmade microscopes to observe microorganisms, which he called 'animalcules.' These observations revealed a hidden world of life too small to be seen with the naked eye and helped pave the way for modern cell theory and microbiology. With real-life connections, such as the study of bacteria and protozoa, and a strong focus on key vocabulary and science literacy, this reading comprehension passage builds students’ understanding of cells and supports the Next Generation Science Standards in life science.

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In the late 1600s, a Dutch scientist named Antonie van Leeuwenhoek made a discovery that changed the way we understand life. Using simple microscopes he built himself, he became the first person to observe tiny living organisms that were invisible to the naked eye. He called these tiny creatures “animalcules,” which means “little animals.” Today, we know them as microorganisms.

Van Leeuwenhoek was not a trained scientist. He worked as a cloth merchant and began using magnifying lenses to inspect fabric. Over time, he improved his lenses and created powerful single-lens microscopes that could magnify objects up to 200 times. He looked at many things under the microscope, including pond water, tooth scrapings, and even rainwater. What he saw amazed him—tiny, moving organisms that no one had ever seen before.

These animalcules included what we now know as bacteria and protozoa. Van Leeuwenhoek carefully recorded what he observed and sent letters to the Royal Society of London. His discoveries opened the door to the world of microbiology and helped lay the foundation for cell theory, which explains that all living things are made of cells.

Van Leeuwenhoek’s work showed that there is a whole hidden world of life too small to see with the eye alone. His curiosity and attention to detail helped scientists realize that cells and microorganisms are part of every living system. Without his work, we might not understand diseases, digestion, or even the environment in the way we do today.

Fun Fact: Antonie van Leeuwenhoek made over 500 microscopes in his lifetime—and some of them still work today!

What tool did Antonie van Leeuwenhoek use to make his discovery?

TelescopeCompassMicroscopeThermometer

What does the word “animalcules” mean?

PlantsLittle animalsWater dropsDust particles

What types of samples did van Leeuwenhoek observe?

Only fabricRocks and fossilsPond water and tooth scrapingsClouds and stars

What were some of the animalcules he discovered?

Atoms and moleculesFungi and insectsBacteria and protozoaBlood cells and veins

What important science field began because of his discoveries?

AstronomyMicrobiologyChemistryGeology

How did van Leeuwenhoek's discoveries connect to cell theory?