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Web of Life    Mystery 2

Mystery 2 image

In this Mystery, students discover the surprising nutrient which accounts for most of a plant's food. In the activity, they conduct an investigation to determine if this nutrient can plausibly account for a plant's weight.

What do plants eat?

4.5 (5501 reviews )
Exploration (20 min)
Activity: Weighing Air (30 min)
Extras (2.3 hrs)
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Start Mystery
Beginning Exploration (1 of 8)
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Beginning Exploration (2 of 8)

DISCUSS (1 of 2):

All that 4 million pounds of wood must have come from somewhere. What do you think plants eat? Do they even eat?

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Beginning Exploration (3 of 8)

DISCUSS (2 of 2):

How could you find out?

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Beginning Exploration (4 of 8)
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Beginning Exploration (5 of 8)

DISCUSS:

Go ahead and take a guess. If the tree had been eating the soil, then what do you think the scientist will notice?

Why do you think this?

Weight of sapling and soil

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Beginning Exploration (6 of 8)
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Beginning Exploration (7 of 8)

DISCUSS:

Do you think that air weighs anything?




What could you do to find out? Can you think of an experiment that would let you weigh air?

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Beginning Activity Prep
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Activity Prep

1. Gather these supplies

pencil1 per class
wooden ruler1 per class
yardstick1 per class
heavy book1 per class
desk DetailsHide details
balloon DetailsHide details
jumbo paper clip DetailsHide details
small binder clip DetailsHide details
medium binder clip DetailsHide details
ribbon or string DetailsHide details
coat hanger, book, jumbo paper clips (optional) DetailsHide details
Weight of Air worksheet 1 per student
Weight of Air answer key 1 per teacher
Teacher instructions handout
For making the scale and balloon corral. 		1 per teacher

2. Print and complete the Before-Class Checklist

Beginning Activity: Weighing Air
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Beginning Activity: Weighing Air
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Beginning Activity: Weighing Air
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Beginning Activity: Weighing Air
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Beginning Activity: Weighing Air
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Beginning Exploration (8 of 8)
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Beginning Complete!

You've completed the Exploration & Activity!

If you have more time, view the assessment, reading and extension activity in the optional extras.

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Beginning Extras

Optional Extras

Below are ideas for extending this topic beyond the activity & exploration you just completed.
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Beginning Extras

Video and discussion: Weighing air on a scale

Discuss: How could you use a scale to weigh air?

Watch these videos to see how one science teacher did just that. Kathy Marvin weighed a deflated basketball.) Then she compared that with a basketball that’s pumped full of air. How much did the air in the basketball weigh?

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Beginning Extras

Dirt Free Gardening

One way to convince yourself that plants don’t eat dirt to grow is to grow a plant without dirt, a practice known as hydroponic gardening. You can make a simple hydroponic garden and grow lettuce in a 2-liter soda bottle.

A homeschooling mom (and former teacher) offers simple instructions for this project here.

If you want to go a little further, testing the pH of your system and adding nutrients, we recommend these detailed instructions from Epic Gardening.

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Beginning Extras

How does tape keep the balloon from popping?

After doing the activity, you may find yourself intrigued by how balloons pop -- and how you can keep them from popping.

You’ll find a short answer to the question of why tape stops the pop from the scientists at University of California Santa Barbara.

If your ears and nerves can take it, balloon popping can be the start of an investigation, like the one described on the Caterpickles blog.

And if you want to assure yourself that this is a reasonable topic for true scientific investigation, check out reports on two scientists’ efforts to understand popping balloons. Here’s an Los Angeles Times report (adult reading level) and a video from the New York Times with exciting popping footage.

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Video Review & Discussion

The beginning of this short video from NOVA reviews material covered in this mystery. To reinforce the lesson, stop the video at 1:25 and discuss von Helmont’s experiment as a class, using the discussion questions suggested on the site.

  • Why did von Helmont think that plants got their nourishment from soil?
  • Why did he eliminate soil as a source of nourishment and focus on water?
  • What did he measure to find out if the willow plant got its nourishment from soil? The remainder of the video introduces photosynthesis, chloroplasts, and carbon dioxide — great topics when your students are ready for them.
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Beginning Extras

Reading: Giant Redwood Trees

Read about how the giant redwood trees are doing these days. This Newsela reading explores how scientists are studying the effects of changes in the Earth’s climate and atmosphere on these trees. Includes a multiple choice quiz and an open-ended question to serve as a writing prompt.

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Image & Video Credits

Mystery Science respects the intellectual property rights of the owners of visual assets. We make every effort to use images and videos under appropriate licenses from the owner or by reaching out to the owner to get explicit permission. If you are the owner of a visual and believe we are using it without permission, please contact us—we will reply promptly and make things right.

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