Plant Growth and Air

Active learning helps fifth graders grasp that plants build their bodies from air because it makes abstract ideas concrete. When students handle soil, measure mass, and observe growth firsthand, they see evidence that contradicts common misconceptions about where plant mass comes from.

• 5th Grade
• Science
• 3 activities
• 15 min–50 min

Learning Objectives

1. Analyze experimental data to evaluate the contribution of air and water to plant mass.
2. Explain the process by which plants convert carbon dioxide and water into plant matter.
3. Compare the mass of soil before and after plant growth to support the claim that plants primarily use air and water for growth.
4. Formulate a scientific claim, supported by evidence, about the primary sources of plant material.

Inquiry Circle

⏱ 40 min·Small Groups

Inquiry Circle: The Van Helmont Mystery

Students are given the data from Jan Baptista van Helmont's 17th-century willow tree experiment. In small groups, they must analyze why the tree gained 160 pounds while the soil only lost 2 ounces, then present their theories.

Prepare & details

If plants grow in soil, why doesn't the dirt in a pot disappear over time?

Facilitation Tip: During The Van Helmont Mystery, have students weigh the soil at the start and end to visibly show that soil mass barely changes, making the air-to-mass connection clear.

Setup: Groups at tables with access to source materials

Materials: Source material collection, Inquiry cycle worksheet, Question generation protocol, Findings presentation template

• Analyze
• Evaluate
• Create
• Self-Management
• Self-Awareness

Inquiry Circle

⏱ 50 min·Small Groups

Station Rotations: Plant Anatomy and Air

Stations include looking at stomata (leaf pores) under a microscope, observing a plant in a sealed jar, and weighing dry vs. wet soil. Students collect evidence at each station to explain how air enters the plant.

Prepare & details

How do trees build heavy trunks out of invisible gases?

Facilitation Tip: In Station Rotations: Plant Anatomy and Air, ask students to trace the path of carbon dioxide from the air into plant structures using labeled diagrams and real specimens.

Setup: Groups at tables with access to source materials

Materials: Source material collection, Inquiry cycle worksheet, Question generation protocol, Findings presentation template

• Analyze
• Evaluate
• Create
• Self-Management
• Self-Awareness

Think-Pair-Share

⏱ 15 min·Pairs

Think-Pair-Share: The Log and the Air

Show a heavy wooden log. Ask: 'If I told you this log is mostly made of air, would you believe me?' Students discuss in pairs and then learn about the carbon in CO2 becoming the wood's structure.

Prepare & details

What role does water play in the structural growth of a plant?

Facilitation Tip: For The Log and the Air Think-Pair-Share, provide a log image and ask students to predict its composition to spark discussion about carbon storage in wood.

Setup: Standard classroom seating; students turn to a neighbor

Materials: Discussion prompt (projected or printed), Optional: recording sheet for pairs

• Understand
• Apply
• Analyze
• Self-Awareness
• Relationship Skills

Teaching This Topic

Teach this topic by starting with student misconceptions, then using hands-on experiments to provide counter-evidence. Avoid overwhelming students with too many terms at once; focus instead on the big idea that plants transform air into solid matter. Research shows that students retain this concept better when they observe mass changes over time and discuss the role of carbon dioxide explicitly.

What to Expect

Successful learning looks like students confidently explaining that plants gain most of their mass from carbon dioxide in the air, not soil. They should use evidence from experiments and discussions to support their ideas and apply the concept to new situations.

Watch Out for These Misconceptions

Common Misconception

During The Van Helmont Mystery, watch for students who assume soil is the main source of plant mass.

What to Teach Instead

Have students weigh the soil at the beginning and end of the experiment. Ask them to compare the soil loss to the plant’s mass gain, guiding them to conclude that most mass must come from another source, such as air.

Common Misconception

During Station Rotations: Plant Anatomy and Air, watch for students who believe water alone provides all the material for plant growth.

What to Teach Instead

At the stomata station, ask students to examine a leaf’s structure and discuss where gases enter. Encourage them to recall that carbon is needed for growth and link it to carbon dioxide from the air.

Assessment Ideas

Quick Check

After The Van Helmont Mystery, present students with the scenario: 'A plant in a pot gained 100 grams over a month, but the soil only lost 5 grams. Where did the other 95 grams come from?' Ask students to write a brief explanation using the terms 'carbon dioxide' and 'mass'.

Discussion Prompt

During The Log and the Air Think-Pair-Share, facilitate a class discussion using the prompt: 'Imagine a giant redwood tree. If most of its mass comes from air, what does this tell us about the importance of the atmosphere for life on Earth?' Encourage students to share their reasoning and connect it to photosynthesis.

Exit Ticket

After Station Rotations: Plant Anatomy and Air, ask students to complete the sentence: 'Based on our experiments, plants grow by taking in ______ from the air and ______ from the soil, using energy from the sun.' Have them briefly explain how this process adds mass to the plant.

Extensions & Scaffolding

• Challenge: Ask students to calculate how much carbon dioxide a classroom plant might absorb in a year, using their growth data and a conversion factor provided by the teacher.
• Scaffolding: Provide sentence frames for students to use during discussions, such as 'The plant gained mass from ______ because ______.'
• Deeper exploration: Have students research how deforestation affects the carbon cycle and present their findings to the class.

Key Vocabulary

photosynthesis	The process plants use to convert light energy, water, and carbon dioxide into glucose (sugar) for food and oxygen.
carbon dioxide	A gas in the air that plants take in through their leaves to use during photosynthesis.
stomata	Tiny pores, usually on the underside of leaves, through which plants exchange gases like carbon dioxide and oxygen with the atmosphere.
biomass	The total mass of organisms in a given area or volume, referring to the material that makes up a plant's structure.