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

• Lesson Assessment and Answer Key
• Video and discussion: Can you think of a way to weigh air on a scale?
• Activity: Dirt Free Gardening
• Reading: What do plants need to grow?
• Video Review & Discussion: A NOVA video lets you review and encourage class discussion.

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?

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.

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.

The beginning of this short video from NOVA reviews material covered in this mystery. To reinforce the lesson, stop the video at 1:07 and discuss van Helmont’s experiment as a class, using the discussion questions suggested on the site.

• Why did van 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.

This reading, free with registration at Readworks, discusses the three things that plants need to grow: water, carbon dioxide, and light.

Vocabulary words and comprehension questions are included.