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Investigating Photosynthesis with Van Helmont

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Cellular Energy: Photosynthesis

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Investigating Photosynthesis with Van Helmont


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You will repeat Van Helmont’s experiment and a more modern follow up experiment to show where plants obtain their mass.

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Now You Know

After completing this tutorial, you will be able to complete the following:

  • Describe Van Helmont’s experiment with the willow tree.
  • Explain that Van Helmont’s experiment showed that plants do not get their mass from the soil.
  • Explain that Van Helmont’s work showed the importance of careful measurement in scientific investigations.  
  • Explain that plants increase their mass mainly through the intake of a substance from the air.

Everything You'll Have Covered

The dates of Van Helmont's life seem to be in dispute. Some sources put his birth as early as 1577, while most sources say he was born in Belgium in 1579 some sources say as late January of 1580. Most sources, however, are in agreement that he died on December 30, 1644. While Van Helmont is most famous for experiments into where plants obtain their mass for growth, he also contributed to science in many other ways. He performed many experiments in chemistry and is said to have been the first to use the word "gas." It is also important to note that in his original experiment Van Helmont dried the soil in a furnace before and after weighing it, and waited five years before reweighing the tree.

Photosynthesis requires carbon dioxide and water and the presences of sunlight to make sugar and oxygen. Even though the elements had not been discovered during Van Helmont's time, it was still known that plants needed water, soil, and sunlight to increase their mass. Van Helmont investigated the role of the water and soil. He concluded that since the weight of the soil had only diminished by ounces and that the Willow tree had gained 164 pounds the mass must have come from the water.

Van Helmont was not the first to make this observation. In 1450, Nicolaus of Cusa, made similar, but not as precise, observations. There is also mention of these phenomena by the early Greeks and Leonardo Da Vinci. What separated Van Helmont from his predecessors was the accuracy of his measurements and the investigative process he employed. Many scientists have since followed up Van Helmont's experiments. Joseph Priestley in 1772was able to show that plants change the chemistry of the air around them in his famous experiments using plants, bell jars, candles, and mice. Melvin Calvin (Calvin Cycle) in 1940 was able to show the pathway carbon takes during photosynthesis by using carbon fourteen as a marker chemical.

Tutorial Details

Approximate Time 20 Minutes
Pre-requisite Concepts Students should be familiar with growth, photosynthesis, and the scientific method.
Course Biology
Type of Tutorial Concept Development
Key Vocabulary air, bell jars, experiments