Pre-Activity 0.2GL: Plant Growth Investigation Setup (45 min over 1 or 2 days)

Target Student Performance

Students plant radish seeds, record initial masses, and let seeds grow for at least 4 weeks. After four weeks, the plants will be large enough to begin the rest of the Plants Unit.

There are two different versions of this Pre-Activity to choose from depending on the depth of instruction you’d like to cover. Please refer to the Background Section at the beginning of this lesson plan for more information about each.

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)

Pre-Activity 0.2GL: Plant Growth Investigation Setup (45 min over 1 or 2 days)

This Pre-Lesson Activity is part of the Gel Protocol (2-turtle) and should only be taught if you have chosen this pathway (see Background Information for details).

Resources You Provide

Large (37mL) test tubes or other clear receptacle (1 per student)
1 packet of gel crystals (hydrated already if completed pre-lesson 1.1) (1 per class)
4 teaspoons of Ionic Grow (1 per class – not necessary if completed pre 1.1)
Gallon of distilled water (1 per class – not necessary if completed pre 1.1)
Bucket or bowl (>1 gallon) to hydrate gel overnight (1 per class – not necessary if completed pre 1.1)
Strainer/colander large enough for hydrated gel (1 per class- not necessary if completed pre 1.1)
Digital scale (to 0.1g) (1 per group)
Grow/Fluorescent Light
Test tube rack
Permanent markers and labels for test tubes
Fresh packets of radish seeds (at least one seed per student or group plus a few more)
Squeeze bottle to water plants

Resources Provided

Setup

For the gel crystals, 1 gram (~1/4 tsp) of crystals absorbs ~70g of water. Only ~0.25g of dry mass goes in to each 37 mL test tube. 1 packet (~17g) makes enough gel to fill ~ 60 37mL test tubes.
Look for 20 X 150mm Pyrex glass test tubes, 37 mL capacity. If those are not available, clear plastic vials or small cups can work.
You will make the nutrient mixture with 4 teaspoons of Ionic Grow to 1 gallon distilled water during class with students (unless you already completed pre 1.1)
Things inevitably go wrong when growing plants. Be sure to plant some extras. At least one extra radish plant per group of students is recommended.
The squeeze bottle (e.g. ketchup bottles work well) is for future maintenance of plants.
Print one copy of the Pre-Lesson 0.2GL Plant Growth Investigation Setup Worksheet for each student.
Prepare your computer, projector, and speakers for the Growing Plants Investigation Video and the Pre-Lesson 0.2GL Plant Growth Investigation Setup PPT.

Directions

1. Use the instructional model to show students where they are in the course of the unit.

Show slide 2 of the Pre-Lesson 0.2GL Plant Growth Investigation Setup PPT.

2. Have students work in groups of four.

Each student will plant one radish seed in the plant gel.

Four plants will allow each group to do at least one of the experimental treatments in Activity 3.2 Plants in the Light and Dark and have multiple measures to compare for Activity 3.4GL Observing Plants’ Mass Changes.

3. Have students calculate the mass of the solid plant gel in their test tubes.

Have students follow the steps in Part A of their Pre-Lesson 0.2GL Plant Growth Investigation Setup Worksheet .

Show students slide 3 of Pre-Lesson 0.2GL Plant Growth Investigation Setup PPT.
Students should use the percentage they calculated from Pre-Activity 0.1 for how much solid is in the hydrated gel (should be ~1.4%). Students should understand that very little solid matter is added to the system through the addition of the Ionic Grow nutrient mixture. Following are our calculations through which you may choose to walk students or which you may just use as your own background knowledge.
Each gram of gel crystals absorbs 70 grams of water, so hydrated crystals are about 1.4% solid mass and 98.6% water. Each gram of water contains 0.015% Ionic Grow solids, so 1 gram of rehydrated gel contains 0.0089 grams of Ionic Grow dry mass.
There are 0.25 grams dry gel crystals + 0.0038 grams dry Ionic Grow = ~0.25 grams dry mass in each 37 mL test tube
Note that radish seeds and the solids in the Ionic Grow mixture turn out to have tiny masses—less than 0.01 grams. Even though the scales show 0.01g precision, they aren’t really that accurate, so the best way to deal with masses less than 0.01 g is to treat them as 0, or too small to measure. Otherwise, students will have a sense of false precision. For the purposes of this activity, when students are recording a mass that is less than 0.01g, they should be writing, “<0.01g.” When doing calculations with this number, they should treat it as a zero.
Tell students the dry mass calculations will be important later as they measure how their plants grow and try to determine where the mass of the growing plants comes from.

4. Have students calculate the mass of all solids in their test tubes.

Have students follow the steps in Part B of their Pre-Lesson 0.2GL Plant Growth Investigation Setup Worksheet .

Show students slide 4 of Pre-Lesson 0.2GL Plant Growth Investigation Setup PPT.
Remind students that the plants will need 3-4 weeks to grow before they are large enough to begin the rest of the Plants unit.
Place the test tubes about 12-16 inches under the grow lights or in a sunny windowsill.

5. Plant maintenance

Use the table in Part C in the Pre-Lesson 0.2GL Plant Growth Investigation Setup Worksheet for students to track their observations and ongoing watering of their radish plants.

Show students slide 5 of the Pre-Lesson 0.2GL Plant Growth Investigation Setup PPT.
The gel is designed to water the plants for at least a week (probably 2) prior to needing additional nutrient mixture input.
Prepare another gallon of nutrient mixture (4 teaspoons Ionic Grow to 1 gallon distilled water) to add if needed to the tubes once most of the mixture has been extracted from the gel by the plants. Add nutrient mixture to the test tubes when the gel has subsided enough (~50% from initial volume) that the plants are in danger of wilting. Ketchup bottles (with the nozzles) work well for adding water. Only add an inch or two of the mixture at a time. Adding to much risks drowning the plants or creating an optimal environment for algal growth.
The percentage of Ionic Grow dry mass in the nutrient mixture is 0.015%. Walk students through the appropriate calculation to determine the dry mass added each time to each system when the radish plants are watered. Note: the dry mass added to the tubes via the nutrient solution will be negligible.

Assessment

There is no assessment for this activity since students are setting up an experiment to learn from later on.

Tips

If many of your students seem convinced that plants will not grow without soil nutrients, you may want to rehydrate a few gel crystals with water only to see if the radish seeds will germinate and start to grow (they should!).
Allow students to take pictures of what they are putting into their test tubes as a reference for later on after plant growth.