Plants | Pre-Lesson 1 - Investigation Setup

Students set up an investigation in preparation for the Plants Unit. Plants will be ready to harvest about four weeks later.

Guiding Question

How does a plant gain mass?

Activities in this Lesson

Note: There are two different pathways to choose from in the Pre-Lesson. Please see the Plants Unit Read Me DocumentStudent Challenges and Teacher Choices in the Plants Unit document and/or the Background Information section below for clarification in making this instructional decision.

Gel Protocol (2-turtle)

    • Pre-Activity 0.1GL: Keeping Track of Water in Solids and Liquids (60 min + overnight or several days)
    • Pre-Activity 0.2GL: Plant Growth Investigation Setup (45-60 min over one or two days)

Paper Towel Protocol (1-turtle)

    • Pre-Activity 0.2PT: Plants Growth Investigation Setup (45-60 min)

Unit Map

Plants Pre-Lesson Unit Map

Target Performances


Target Performance

Pre-Lesson 1: Investigation Setup

Pre-Activity 0.2GL: Keeping Track of Solids in Mixtures

Students will distinguish between solid mass (or dry mass) and total mass of materials consisting of water mixed with solid materials and use measurement techniques to determine the mass of solids in the mixtures.

Pre-Activity 0.2GL: Plant Growth Investigation Setup

Students will make initial measurements of the dry mass of radish seeds and growth media and start plants growing.

Pre-Activity 0.2PT: Plant Growth Investigation Setup

Students will make initial measurements of the dry mass of radish seeds and growth media and start plants growing.

NGSS Performance Expectations

Middle school

  • MS. Matter and Energy in Organisms and Ecosystems. MS-LS1-6. Construct a scientific explanation based on evidence for the role of photosynthesis in the cycling of matter and flow of energy into and out of organisms.

High school

  • HS. Chemical Reactions. HS-PS1-7. Use mathematical representations to support that claim that atoms, and therefore mass, are conserved during a chemical reaction.

Three-dimensional Learning Progression

The plants that are set up in the Gel Protocol (2-turtle) Pre-Lesson need about four weeks to grow to a point where they have gained enough mass to produce significant results in Lesson 3. The Paper Towel Protocol (1-turtle) may take as few as 2 weeks to achieve significant mass gain results. Thus, the Pre-Lesson(s) should be conducted one to three weeks before you plan to begin Lesson 1 of the Plants Unit, depending on which pathway you choose.

Students may begin this Unit thinking that plants build the majority of their mass from minerals and nutrients in the soil. Although atoms from soil minerals and water contribute trace amounts of materials during biosynthesis (e.g., nitrogen, potassium, and phosphorous from the soil), the majority of biomass is built from carbon from CO2 in the air. By growing plants from seeds and taking measurements of plant dry mass and the dry mass of the rest of the system, this investigation gives students evidence that plants do not build their mass from the growing medium or water. Lesson 4 (Photosynthesis & Cellular Respiration) and especially Lesson 5 (Biosynthesis) give students further evidence that plants build their mass from materials they get from the air.

This Pre-Lesson, then, sets up for students not only the actual growing of the plants, but it also introduces to students some foundational knowledge about the importance of measuring a plant's dry mass. Students will take some initial measurements of the plant systems they are setting up as a reference for use in Lesson 3. In preparation for the investigations in Lesson 3, keep in mind that inevitably things go wrong when growing plants, so make sure to plant some extra radishes (we recommend one extra per group of students). Additionally, you may want to have some extra growing plants in the classroom or at home that are available to potentially do the Plants in the Light and Dark investigation (Activity 3.3). If you decide to have students harvest their radish plants first (in Activity 3.2), they will not have their own radish plants available for Activity 3.3. Therefore, they will either need to rely on the extras that you plant in this Pre-Lesson, or on other growing plants that are available in the classroom or that are brought in from home.

There are two pathways from which to choose when implementing this Pre-Lesson, which will then extend into Lesson 5. The storyline supporting each pathway is the same: students will discover that their radish plants end up with more dry mass in them than they introduced into the system. Where did that mass come from? In Lesson 5, the task for students will be to explain where this mass came from. In this Pre-Lesson, each pathway will help students establish a foundation on which to understand that the mass didn't come from the materials they put into the system. Each pathway will also utilize a text and/or a video to help establish this problem for students. However, each pathway will engage students in different levels of measurements and calculations in order to meet this same goal.

You may choose a pathway based on the amount of instructional time you have to teach the unit, the complexity of measurements and calculations your students can handle while still understanding the underlying concept, or the learning goals you have for your students in this unit. Please refer to the following table for a brief outline of each pathway in the Pre-Lesson.


Activities to Complete


Estimated Time

Gel Protocol (2 turtle)

Pre-Activity 0.1GL & Pre-Activity 0.2GL

Students will find the percentage of dry mass in various mixtures, including the gel and nutrient solution used in this setup. They will use these percentages to calculate the dry mass of their own materials. Students grow individual radish plants in test tubes.

60 min + overnight or several days &

45 min

Paper towel Protocol (1-turtle)



Pre-Activity 0.2PT

The teacher will guide students through taking group measurements of the dry mass of each material (seeds and paper towel) in the system. Groups of students grow multiple (~20) radishes in small aluminum tins and brown paper towel.

45 – 60 min.


The following table is excerpted from the Plants Unit Front Matter document and is also in the Student Challenges and Teacher Choices in the Plants Unit document. It illustrates the options in the Pre-Lesson and how they will impact a sequence of Pre-Lesson and Activities 3.1, 3.2, and 3.4. Please refer to the Plants Unit Front Matter document and the Student Challenges and Teacher Choices in the Plants Unit document for more information about how you might make this choice.

Unit Table for Plants Pre-Lesson

A note on mass and weight: Grams and kilograms in the SI (metric) system are units of mass—the amount of matter in a system. On the other hand, pounds and ounces in the English system are units of weight—the force of gravity on a particular mass. As long as gravity doesn’t change, these units are interconvertible: The force of gravity on a 1 kg mass is about 2.205 pounds. Since most American students are more familiar with the English units of weight, we sometimes use “weigh” and “weight,” especially when encouraging students to express their own ideas. When referring to measurements in grams, we use “mass” as both a verb and a noun.

Key Carbon-Transforming Processes: Photosynthesis

Key Ideas and Practices for Each Activity
Content Boundaries and Extensions