How can we create a mini-ecosystem using household goods?
Background: Making a Soda Bottle Terrarium
When a plant grows, be it inside or outside, there is typically no good way to view how the system is functioning below the surface of the soil. Creating a terrarium with recycled items and common household supplies provides a fantastic view of how a plant’s root system is functioning, as well as other environmental phenomena. In doing so, students can see how a plant functions within a given environment, while observing how the plant itself creates the environment it subsequently inhabits.
Students will be able to...
Create a closed environment ecosystem with household items
Observe stages of plant growth, as well as how plants construct their own living environments
Understand the cycling of non-living materials
terrarium /təˈrerēəm/ noun. - an encased ecosystem with living and non-living entities
🌎Latin roots: terra (Earth) , -arium (place)
ecosystem /ˈēkōˌsistəm/ noun. - a community of living things, along with their nonliving environments, that collectively influence the abundance and availability of natural resources, as well as one another’s behavior patterns and living conditions
rhizosphere /ˈrīzəˌsfir/ noun. - the realm of biological interaction and nutrient exchange occurring in the soil region where plant roots and various microorganisms exist in association
1. Gather your materials. You may be able to get these on a walk around your neighborhood. You will need the following supplies:
2-liter soda bottle with cap (1) · marker · scissors · pebbles, wood chips, sand, rocks (optional, ½ cup or more) · sphagnum peat moss or other moss (optional, 1 cup or more) · potting soil (1-3 cups or more) · seeds and/or seedlings · water
Closed vs Open System … In science, it is important to understand the concept of both closed and open systems. A perfect closed system means that nothing -- no other species or natural resource -- enters or exits the system from/into the surrounding environment. An open system, on the contrary, means that this exchange of materials does happen.
Is a terrarium closer to a closed or an open system?
If it is open -- or when you open the system yourself -- what might be leaving or entering the system?
2. Watch the following Youtube video to see a demonstration of how to make a terrarium. Then, follow along with the rest of the lesson below.
3. Prepare your soda bottle terrarium. Use a marker to draw a line around the middle of the bottle. If necessary, use a ruler or another guiding item (like a coffee mug) to measure your bottle’s halfway point. Using scissors, carefully cut the 2-liter bottle in half at your marked line. If you plan to use more than the specified materials, cut your bottle so that the bottom half is larger.
4. Put the materials into your terrarium.
First, place your larger rocks and pebbles in the bottom half of the bottle, if you have them.
Next, add sand, if you have it.
Add a layer of moss, if you have some.
Next, place the soil on top of your rock/sand/moss filter. If you are using seeds, plant them into the soil-- consider using 5-10 seeds, depending on the plant. If you are using a seedling, put the plant into the terrarium and add soil as needed to stabilize it. Feel free to try both of these strategies at the same time! Aim for 2-4 inches of soil.
If you have more moss, more rocks, a plant mascot, or other decorative items, place these on your top layer of soil.
5. Place the top of your terrarium back onto the bottom half. It may be easiest to put the top half on the outside of the lower half. Cut a small slit or two in the top half in order to fit it, if necessary.
6. Mist/water your seed and terrarium walls, and place it in a sunlit -- but not direct sunlight -- and warm area. You can remove the cap of the terrarium to water your seedlings. You want to create a moist but not damp environment. Move your terrarium as needed to give it around 6 hours of sunlight every day.
💧🌡It’s getting hot in here … As the system warms in a lit area, what do you observe about the movement of water in the system?
Evaporation: is the surface of the soil becoming dryer? (liquid → gas transition)
Transpiration: are the leaves on the plant becoming dryer? (liquid → gas transition)
Condensation: is there moisture forming on the top of the terrarium? (gas → liquid transition)
Precipitation: is there liquid falling from the top of the terrarium? (movement of liquid)
Percolation: is there liquid flowing through the soil? (movement of liquid)
7. Monitor the system, adding water and providing fresh air when necessary.
↟↟↟Let’s get to the root of this … As your plant grows larger above the soil, the roots will also grow longer in order to support the larger plant with more nutrients and water. Special things happen in this root zone, aka the rhizosphere.
In order to bring in more water, many plants have formed symbiotic relationships with particular species of fungi.
Plants facilitate this association, called mycorrhizae, by providing the fungus with sugars for its growth.
Meanwhile, the fungus channels water to the plant. With the association, the plant effectively expands the surface area of its root system.
Do you see fungal or other organisms around your plant’s roots? What patterns do they make in the soil?
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