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Cultivating Inquirers | Science Standards | Mini-Lesson Stations

Mini-Lesson Stations

Exploring the Basics

Before setting up a complete hydroponics system, you may want to involve students in some short hands-on activities to explore some of the key factors affecting hydroponic setups. This section offers some ideas for "stations" that could be set up as learning centers before or during your hydroponics study. The stations are in no particular order and can be modified easily to suit your students' abilities, interests, and prior knowledge.

Station 1: Super Soup: Mixing the Nutrient Solution

Purpose: To learn correct procedures for combining the materials for a hydroponic nutrient solution

Materials: Nutrients, in the form of commercial powdered or liquid hydroponic mixtures or as individual mineral salts, water, containers, measuring equipment, stirring rods

Procedure: Have students follow container directions or a recipe for mixing nutrients, being careful to measure exactly.

Challenge Questions: What are nutrients? Which of these might you investigate in the classroom? What do you think might happen if you use a stronger nutrient solution than called for? A weaker solution? How might you design your own "secret formula" to grow plants? How would you measure your success?

Station 2: pH: The Acid Test

Purpose: To learn how to measure and change pH in a liquid

Materials: pH paper or test kit, vinegar, baking soda, containers, distilled water

Procedure:

Teach students how to find pH. Provide about 100 mL of distilled water per container. Dip a pH paper strip into the liquid being tested and compare the color change to the chart provided with the paper, or follow directions on your pH test kit.
Next, challenge students to change the pH in some prescribed way (e.g., lower pH to 6 or raise it to 7), keeping track of the number of drops or pinches of baking soda needed. (The solution will fizz when vinegar and baking soda mix, much to students' delight.) Ask students to test and experiment with the pH of the different nutrient mixtures.
You may want to precede this activity by encouraging students to brainstorm, then gather common solutions to test (e.g., orange juice, shampoo, household cleaners) to give them a better foundation for understanding the range of pH numbers.

Challenge Questions: How might a very acidic solution affect your hydroponically grown plants? A solution with a higher pH? How could you set up an investigation to find the answers to these questions? In what other situations might you need to know the pH of a solution? How else might scientists use pH?

Station 3: Plant Perspiration

Purpose: To discover that water can be lost from leaves through transpiration in a hydroponic setup, how to compensate for that loss, and explore the purpose of transpiration

Materials: Samples of different leaves with stems, graduated cylinders (one more than you have leaf types), modeling clay, water

Procedure: This investigation takes about 2 days.

Fill each graduated cylinder to the same level, and mark the water line.
Wrap the clay around each leaf stem and insert the leaf and clay into the mouth of the graduated cylinder. Make sure that the leaf stem is well below the water level and that there is no air space between the stem and the clay or between the clay and the cylinder. As a control, simply plug one cylinder without a leaf.
Place all graduated cylinders in a sunny windowsill and observe the level of the water in each over the 2 days. Water will move up the stem of the leaf and out through small pores in the leaves (called stomates). Students will see varying amounts of water loss from the cylinders.

Challenge Questions: What does this investigation indicate about leaves and water? How does transpiration affect the air plants use? Why did we have a plain cylinder with no leaf in it? (This served as a control, to show that all water loss was actually through the stem and leaf). What do your observations tell you about what might happen in a hydroponic system that you set up? How might you deal with replacing the moisture lost through transpiration?

Station 4: A Medium Well-Done

Purpose: To investigate different kinds of media for their water-retaining properties

Materials: A variety of potential hydroponic media (e.g., sand, perlite, cloth, rockwool, aggregate), magnifying glasses, water, containers, waxed paper or recycled foam trays for a work surface

Procedure:

Provide or ask the students to bring in a range of materials other than soil that they think might support plant growth.
Have them examine the various media with hand lenses, making observations and sketches of the different structures.
Ask students to predict which might absorb the most water, then choose one to try using in a simple hydroponic system.

Challenge Questions: Can you explain why you chose what you did? Can you invent ways to compare the water-absorbing properties of each medium? If you could design the perfect hydroponic medium, what would it be like?

Station 5: Let There Be No Light

Purpose: To observe the effect of light on plant root development

Materials: Two identical clean glass jars, water-absorbent polymer crystals, two similar ivy cuttings, black plastic or other dark material sufficient to wrap one of the jars

Procedure: This will take about three weeks.

Add 1 to 2 teaspoons of polymer crystals to each jar and fill it with water. (The crystals turn jelly-like when wet.)
After the crystals have swelled to fill each jar, gently poke a piece of ivy into each.
Cover one jar with black material and leave the other uncovered. Place both jars on a window and observe. (Students should note that the roots in the covered jar form more strongly and fully. This is because light is actually a deterrent to active root growth.)

Challenge Questions: How do the roots in the two jars compare? Why do you think roots formed the way they did? How might the results of this investigation influence the way you build your own hydroponics unit?

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