1. Plants Unit Activity 3.2GL Observing Plants’ Mass Changes, Part 1
Carbon: Transformations in Matter and Energy
Environmental Literacy Project Michigan State University
Plants Unit Activity 3.2GL Observing Plants’ Mass Changes, Part 1
Image Credit: Craig Douglas, Michigan State University

2. Plants Unit Map You are here (down the triangle) Application
Lesson 2: Foundations: Zooming into Organisms
Lessons 4 & 5: Explaining How Plants Make Food, Move, Function, and Grow
Lesson 3: Investigating Plants
Lesson 1: Pretest and Expressing Ideas
Lesson 1: Pretest and Initial Ideas
Lesson 6: Explaining Other Examples of Plant Growth and Functioning
Observations
Patterns
Models
Data from mass of plants growing from seed.
Data from plants in the light and dark with BTB.
Plants gain mass (more).
Soil loses mass (less).
Plants take in CO2 in the light.
Plants release CO2 in the dark.
Photosynthesis
Biosynthesis
Cellular Respiration
Pre Lesson: Investigation Set-Up
(up the triangle)
Inquiry
Evidence-Based Arguments
Model
(down the triangle)
Application
Observe
Coach
Use the instructional model to show students where they are in the course of the unit.
Show slide 2 of the 3.2GL Observing Plants’ Mass Changes, Part 1 PPT.
Pre Lesson
Pretest
Establish the Problem
Found-ational
Knowl-edge and Practice
Predict & Express Ideas
Fade
Post test
Maintain
Next Unit

3. Harvesting the plants
Grasp the radish stem close to the gel and carefully slide or wiggle the entire radish plant and the attached gel out of the test tube.
Keeping the plant intact, remove the gel from the plant roots by gently squeezing the roots between your thumb and fingers.
Save the gel in a small container for massing.
Have students harvest the plants.
Follow the instructions in Part A of the 3.4GL Observing Plants’ Mass Changes, Part 1 Worksheet.
Show slide 3 and 4 of the PPT, which has the instructions and pictures of the process.
You may want to demonstrate how to remove the gel from the roots to preserve as much of the plant as possible. Emphasize to students that they do not want to pull on the roots or they will break. Squeezing will generally not break roots.
The Worksheet prompts students to mass their hydrated gel after separating it from their plants and estimate the dry mass by using the percentage dry mass provided = 1.4%. Alternatively, you could dry the gel in an oven and use the scales to measure this directly.
The worksheet also prompts students to mass the plant after harvesting. An estimated dry mass percentage of a radish seedling (7%) is provided. Students can use this value to estimate the dry mass present in their seedling. Make sure students save their initial measurements in a safe place as they will return to them in Activity 5.1.

4. Harvesting the plants
Lay the harvested plants out on paper towel, parchment paper, or roll up in envelopes or small paper bags to dry, arranging them so that they do not touch each other. Use a marker to label your plants for massing in a later activity.
Allow the plants to dry in a sunny windowsill or drying oven.
 Have students harvest the plants.
Follow the instructions in Part A of the 3.4GL Observing Plants’ Mass Changes, Part 1 Worksheet.
Show slide 3 and 4 of the PPT, which has the instructions and pictures of the process.
You may want to demonstrate how to remove the gel from the roots to preserve as much of the plant as possible. Emphasize to students that they do not want to pull on the roots or they will break. Squeezing will generally not break roots.
The Worksheet prompts students to mass their hydrated gel after separating it from their plants and estimate the dry mass by using the percentage dry mass provided = 1.4%. Alternatively, you could dry the gel in an oven and use the scales to measure this directly.
The worksheet also prompts students to mass the plant after harvesting. An estimated dry mass percentage of a radish seedling (7%) is provided. Students can use this value to estimate the dry mass present in their seedling. Make sure students save their initial measurements in a safe place as they will return to them in Activity 5.1.

5. Record your observations
Things to consider:
How much have your plants grown?
Which parts of the plant are the largest? Roots, stems, leaves?
What colors are your plants? Do you expect that to change as they dry?
Has the gel changed from when you planted the radish seeds?
Have students record their observations and estimate dry mass of gel and plants.
Record observations of the plants in Part B of 3.4GL Observing Plants’ Mass Changes, Part 1 Worksheet.
Show slide 5 of the PPT, which lists a few observation idea starters.
Dry the plants.
Students will be able to estimate the dry mass of their plants based on wet mass and compare this value to an actual dry mass they record.
Plants individually labeled can be placed in a small paper bag or envelope on a windowsill to dessicate or can be dried overnight at the lowest temperature (<170 degrees F) in a home oven. IF YOU USE AN OVEN—make sure that the material you place the plants on will not burn and start a fire! Windowsill plants will take a few days to dry if small, but may take longer if they are large.
Note: Radish plants contain only about 7% dry mass, so in order for most classroom scales to even record the dry mass of a single dried plant, the starting masses of the plants should be at least 0.75g. If your plants are smaller, either mass multiple plants together or use the 7% dry mass calculation to estimate dry mass from wet.
(Optional) Dry the gel.
Students may also want to desiccate their gel to see if the mass of the gel in their tubes changed over time and to see if they come up with a similar dry mass percentage (~1.4%).
The gel desiccates best in an oven at low heat (~200 degrees or less) for at least 3 hours. Be aware that the desiccated gel will stick to any surface it is dried on, so students will have to mass the drying surface (non-flammable!) prior to placing the gel on it. Aluminum foil or parchment paper (labeled with the student name or a unique number) works well.
After drying the plants/gel, continue with Activity 3.4.
Since it may take several days for the plants to dry, there are options for what to do with your students while waiting. You may move on to Activity 3.3 and conduct the Light and Dark Investigation. Or, if you started with Activity 3.3 first, you may move on to Lesson 4 which focuses on following up results from the Light and Dark Investigation (Activity 3.3) with explanations of photosynthesis and cellular respiration. Later, students will complete Evidence-Based Arguments for this investigation (Activity 3.5) and Explanations of biosynthesis in plants (Activities 5.1, 5.2, and 5.3). See the Plants Unit Read Me file for more information about this decision.