Plants | Lesson 3 - Investigating Plants

Students conduct an investigation about plants in the light and dark and about mass changes. The focus of this lesson is to make observations and prepare data to be used as evidence for their explanations in Lessons 4 and 5.

Guiding Question

What happens when plants are left in the light and in the dark, and where does a plant’s mass come from?

Activities in this Lesson

Note: There are two different pathways to choose from in Lesson 3. Please see the Plants Unit Front Matter and/or the Background Information section below for clarification in making this instructional decision.

  • Activity 3.1: Predictions and Planning about Radish Plants Growing (50 min)
  • Activity 3.2: (GL or PT): Observing Plants’ Mass Changes, Part 1 (30 min)
  • Activity 3.3: Observing Plants in the Light and Dark (60 min)
  • Activity 3.4: (GL or PT): Observing Plants’ Mass Changes, Part 2 (45 min)
  • Activity 3.5: Evidence-Based Arguments About Plants (50 min)

Unit Map

Plants Lesson 3 Unit Map

Target Performances


Target Performance

Lesson 3 – Investigating Growing Radish Plants (students as investigators and questioners)

Activity 3.1: Predictions and Planning about Radish Plants Growing

Students develop hypotheses about how matter moves and changes and how energy changes when radishes move and grow and make predictions about how they can use their investigation tools—digital balances and BTB—to detect movements and changes in matter.

Activity 3.2 (PT or GL): Observing Plants’ Mass Changes, Part 1

Students harvest their radish plants and dry down the plants and the paper towel or gel in preparation for Activity 3.4.

Activity 3.3: Observing Plants in the Light and Dark

Students observe how plants affect BTB in the light and dark, identify patterns in data, and reach consensus with other groups about their results.

Activity 3.4 (PT or GL): Observing Plants’ Mass Changes, Part 2

Students measure the dry weight of harvested plants and of paper towels or gel, identify patterns in data, and reach consensus with other groups about their results.

Activity 3.5: Evidence-Based Arguments about Plants

Students (a) use data from their investigations to develop evidence-based arguments about how matter moves and changes and how energy changes when plants grow, move, and function; and (b) identify unanswered questions about matter movement and matter change that the data are insufficient to address.

NGSS Performance Expectations

Middle school

  • MS. Structure and Properties of Matter. MS-PS1-1. Develop models to describe the atomic composition of simple molecules and extended structures.
  • MS. Chemical Reactions. MS-PS1-2. Analyze and interpret data on the properties of substances before and after the substances interact to determine if a chemical reaction has occurred.
  • MS. Chemical Reactions. MS-PS1-5. Develop and use a model to describe how the total number of atoms does not change in a chemical reaction and thus mass is conserved.
  • MS. Matter and Energy in Organisms and Ecosystems. MS-LS1-7. Develop a model to describe how food is rearranged through chemical reactions forming new molecules that support growth and/or release energy as this matter moves through an organism.
  • MS. Matter and Energy in Organisms and Ecosystems. MS-LS2-3. Develop a model to describe the cycling of matter and flow of energy among living and non-living parts of an ecosystem.

High school

  • HS. Chemical Reactions. HS-PS1-4. Develop a model to illustrate that the release or absorption of energy from a chemical reaction system depends upon the changes in total bond energy.
  • HS. Chemical Reactions. HS-PS1-7. Use mathematical representations to support the claim that atoms, and therefore mass, are conserved during a chemical reaction.
  • HS. Structure and Function. HS-LS1-2. Develop and use a model to illustrate the hierarchical organization of interacting systems that provide specific functions within multicellular organisms.
  • HS. Matter and Energy in Organisms and Ecosystems. HS-LS1-5. Use a model to illustrate how photosynthesis transforms light energy into stored chemical energy.

Three-dimensional Learning Progression

This lesson provides students with experiences to observe and to collect data which will support them in their next lesson when they construct their explanations about photosynthesis and cellular respiration. They will observe that plants “breathe” (i.e., exchange gases with air) differently in the light and in the dark.

This lesson includes two PEO (Predict-Explain-Observe) Inquiry Activity Sequences with the final E (Explain) occurring in the next two lessons. We will consistently focus on the idea that understanding carbon-transforming processes involves answering the Three Questions:

  • The Matter Movement Question: Where are molecules moving? (How do molecules move to the location of the chemical change? How do molecules move away from the location of chemical change?)
  • The Matter Change Question: How are atoms in molecules being rearranged into different molecules? (What molecules are carbon atoms in before and after the chemical change? What other molecules are involved?)
  • The Energy Change Question:
    What is happening to energy? (What forms of energy are involved? What energy transformations take place during the chemical change?)

The investigations in all units will make use of two essential tools:

  • Digital balances. Students can detect movement of atoms (the Matter Movement Question) by measuring differences in mass. This Activity will ask students to harvest their plants to prepare for future dry massing.
  • Bromothymol blue (BTB). This is a liquid indicator that changes from blue to yellow in response to high levels of CO2. Thus, changes in BTB can partially answer the Matter Change Question by detecting whether there is a chemical change that has CO2 as a reactant or product.
Content Boundaries and Extensions

Talk and Writing

At this stage in the unit, the students will complete the inquiry sequence for Plant Investigations—they will go up the triangle. This means they will go through the Predictions Phase, the Observations Phase, and the Evidence-Based Arguments Phase. The tables below show specific talk and writing goals for these phases of the unit.

Talk and Writing Goals for the Predictions Phase

Teacher Talk Strategies That Support This Goal

Curriculum Components That Support This Goal

Treat this as elicitation and brainstorming (like the Expressing Ideas Phase), but with more directed questioning.

Now that we have set up the investigation, we want to predict what we think will happen to matter and energy.

Three Questions Handout

Predictions and Planning Tool

Elicit a range of student ideas. Press for details. Encourage students to examine, compare, and contrast their ideas with the ideas of other students.

Who can add to that?

What do you mean by _____? Say more.

So I think you said _____. Is that right?

Who has a different idea?

How are those ideas similar/different?

Who can rephrase ________’s idea?

Investigation Video (selected sections)

Encourage students to provide evidence that supports their predictions.

How do you know that?

What have you seen in the world that makes you think that?


Have students document their ideas to revisit later.

Let’s record our ideas so we can come back to them and see how our ideas change.

Predictions and Planning Tool