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ACTIVITY: Can Plants Grow Without Soil?

NGSS Science and Engineering Practices:

NGSS Crosscutting Concepts:

NGSS Disciplinary Core Ideas:

Phenomenon:

Plants in a sunny environment can grow with just air and water!


Inquiry:

What do plants need to grow?


Guiding Questions:

  1. What do you think plants need to grow?
  2. What is it that plants are getting from the soil? 
  3. What do plants get from the air? 

Common Misconceptions About Plant Growth
  • Students may think that plants need soil to build their body mass. This is especially complicated because animals get the building blocks 
  • Students may not recognize that there are components in the air that plants need to grow. Plants use the carbon from CO2, combined with water, to build their body mass.

Activity:

Establish a simple system to grow plants only in water. Then, manipulate other variables to explore what affects growth.

Recommendations:
  • <p>Fig 1. A world wrapped in plastic is not a healthy world. Avoid using single use plastics when you can, and if it canʻt be avoided, re-use and recycle it.</p>In an attempt to limit single use plastics, this activity is written to encourage recycling efforts. A student assignment could be to find already used soda bottles to re-use for this activity and discussions could incorporate the importance of re-using and recycling. 
  • This activity requires care and maintence over time, as it may take two weeks or more to see ample plant growth.
  • The following instructions are written for the use of a basil plant, as they grow quickly and easily. Further investigation could be conducted to grow different plants.
  • This activity is designed to be the first of a series of activities to explore this performance expectation. The activities Build a Hydroponic System and Aquaponics in a Bottle build on this base understanding. 

Materials:

  • Basil plant clippings
  • Recycled 2L bottles (2 per group)
  • Small glass cups (2 of the same size per group)
  • Scissors or knife (teacher supervision required to cut hole in bottle)
  • Ruler
  • Permanent marker
  • Data sheet

     

  • Mesh material (for shade cloth; can use cheesecloth)
  • Nutrients (miracle-gro from hardware store is fine)
  • Metal or silicone straw

Procedure:

  1. <p>Fig. 2. Measure the basil from base to tip of the stem, ignoring leaves.</p>Use a ruler and scissort to cut your basil clippings so they are the same size. Measure from the base to the tip of the stem, without including leaves.
  2. Write down the length of your basil clippings on your data sheet.
  3. Add about an inch of water to the bottom of both glasses. Be sure both cups have an equal amount of water.
  4. Draw a line on the glass to mark the water level. As water evaporates over time, refill water up to the line.
  5. Place one basil clipping in each glass so the base of the stem is submerged.
  6. Cut the top off of your recycled 2L bottles to create the ʻgrow domesʻ for your plants. Clean the domes.
  7. With help from an adult, invert the bottles and cut a hole on the side large enough that a straw can fit through. Try to keep the hole small.
  8. Place a ʻgrow domeʻ over top of each two basil plant.

<p>Fig. 3A. Can basil clippings in a glass of water continue growing?</p><br />
<p>Fig. 3B. A model 'grow-dome' with a hole for a straw.</p><br />

Note to teachers:

This activity set-up forms the basis of an experiment to determine what factors influence plant growth. From here you can manipulate variables and compare what plants need to grow. Student groups can conduct different trials and compare results with the rest of the class. Teachers may want to demonstrate their own version first and use that set-up as the control, with no manipulations, whic can then be used to compare with the student results.

​Manipulations:

  1. Each group will choose or be assigned to apply a manipulation to one of the two basil plants.
  2. Label each glass and corresponding grow-dome A or B. Apply manipulations to the plant labeled A. Don't mix them up!
  3. Create a model system of the control as a demonstration:
  • Control: No treatment
    a. Allow both plants to grow under the 'grow domes' without changing anything between them.
    b. Keep the water levels at the line drawn on each glass.
    c. Measure plant A and B periodically and write the heights on your data sheet.
     
  1. Split class into groups to manipulate the three variables of carbon dioxide (CO2), nutrients, and light. More than one group can explore the same variable. This creates replicates, an important componant in scientific studies.
  • Group #1: CO2
    a. Using the metal or silicone straw, blow into plant A to add CO2.
    b. Set up a schedule so you can add CO2 as often as possible at regular and consistent intervals

  • Group #2: Nutrients
    a. Add nutrients to plant A at regular intervals (once a week will be fine, but can experiment with different intervals).
     
  • Group #3: Light
    a. Drape the mesh cloth over plant A to limit the amount of light available. 
     

Further Investigations:

Extension A: Grow your plant as fast as possible

  • Using data from your class trials, combine nutrients, CO2, and light to grow your plant as fast as possible.

Extension B: Explore your plant's need for water

  • Choose another variable you would like to manipulate, make a plan to explore that experiment.

Extension C: Explore your plant's need for water

  1. Transplant your plants to soil. 
  2. Saturate both plants' soil with water.
  3. Continue to water plant B, but stop watering plant A. 


Activity Questions:

  1. What variable did you test in your experiment?
  2. Which of your plants (A or B) grew more? By how much? 
  3. What else did you notice about the structure of your plant? Describe the growth of both plants (hint: look at other structures like the roots or leaves).

<p>Fig. 4A. It's important to observe different aspects of plant growth in your experiment.</p><br />
<p>Fig. 4B. How do the root structures differ between treatments?</p><br />

  1. How do your results compare to the other trials that looked at the same varialble?
  2. How do your results compare to the other variables that were tested?
  3. What variables contribute to plant growth? Use data from your class' experiments to support your statement.
  4. Why is it important to control as many variables as possible in an experiment? (Hint: why did each group look at only one variable?)
  5. What is the minimum that plants need to grow?
Exploring Our Fluid Earth, a product of the Curriculum Research & Development Group (CRDG), College of Education. University of Hawaii, 2011. This document may be freely reproduced and distributed for non-profit educational purposes.