A bottle ecosystem is a small sealed terrarium that lets you observe how living and nonliving parts of an ecosystem interact. Inside the bottle, plants, soil, water, air, and decomposers form a miniature system that can change over days and weeks. This project matters because it makes invisible cycles, such as water movement and nutrient recycling, easier to see.
By tracking changes for 4 weeks, students can connect observations to real ecosystem processes.
Understanding Ecosystem in a Bottle Project
The bottle receives energy from light, but it receives almost no new matter after it is sealed. This difference is important. Light gives plants the energy to build sugars in their leaves.
Those sugars support growth and later become food for microbes when old leaves or roots die. Plants use some sugar themselves through respiration, including at night when there is no light. Respiration returns carbon dioxide to the air inside the bottle.
This means the air changes through the day. In strong light, plants often use carbon dioxide faster. In darkness, respiration continues in plants, fungi, and bacteria.
The soil is much more than a place that holds roots. It contains tiny spaces filled with air and water. Roots need oxygen in these spaces to stay healthy.
If the soil is soaked for too long, water fills the spaces and roots can struggle to respire. This can lead to yellow leaves, drooping stems, or rotting roots. Microorganisms in the soil break down dead material.
They release mineral nutrients that roots can absorb. Decomposition is usually faster when soil is warm and damp, but extremely wet soil can slow some decomposers because less oxygen is available. A bottle may look still, yet many changes are happening below the surface.
Good observations turn this project into evidence rather than a collection of impressions. Record the same features at the same time each day or every few days. Count leaves, measure plant height, note leaf color, and describe moisture on the glass.
Use a ruler for height and take photos from the same position when possible. Condensation does not always mean the plant has enough water. It shows that water has evaporated and cooled on the bottle wall.
Compare where droplets form, how long they remain, and whether the soil surface becomes dry. Keep a table with dates, measurements, and brief notes. Graphing height over time can reveal trends that are hard to notice by eye.
A fair comparison needs a control group. The control uses normal conditions, while another bottle has one planned change. For example, compare two bottles with the same soil, container size, plant type, and starting water amount, but place one in lower light.
Do not change light, water, and plant species in the same comparison. If several conditions differ, the cause of a result is unclear. Use more than one bottle for each condition if materials allow, since individual plants vary naturally.
Watch for limits in your conclusion. Four weeks can show early responses, but it may not show long term balance. Mold, leaf drop, and slow growth are useful results because they show that resources, organisms, and conditions affect one another.
Key Facts
- Photosynthesis: carbon dioxide + water + light energy -> glucose + oxygen.
- Cellular respiration: glucose + oxygen -> carbon dioxide + water + energy.
- In a sealed bottle, water cycles by evaporation, condensation, and dripping back into the soil.
- Plants need light, water, carbon dioxide, nutrients, and space to grow.
- A fair test changes only one independent variable at a time, such as water amount, light level, or plant species.
- Percent change = ((final value - initial value) / initial value) x 100%.
Vocabulary
- Terrarium
- A terrarium is a clear container that holds plants, soil, and water to model a small ecosystem.
- Ecosystem
- An ecosystem is a community of living organisms interacting with each other and with nonliving parts of their environment.
- Condensation
- Condensation is the change of water vapor into liquid droplets when it cools on a surface.
- Decomposer
- A decomposer is an organism, such as a fungus or bacterium, that breaks down dead material and returns nutrients to the soil.
- Variable
- A variable is a factor in an experiment that can be changed, measured, or kept the same.
Common Mistakes to Avoid
- Adding too much water, which can flood the soil and reduce the oxygen available to roots and decomposers.
- Changing several variables at once, which makes it impossible to know whether water amount, light, plant species, or another factor caused the result.
- Placing the bottle in harsh direct sunlight, which can overheat the sealed system and cook the plants instead of helping them grow.
- Opening the bottle repeatedly, which breaks the sealed-system model and changes the water, air, and microorganism balance inside.
Practice Questions
- 1 A student adds 60 mL of water to one bottle and 90 mL to another identical bottle. How many more milliliters of water does the second bottle receive, and what percent more water is that compared with the first bottle?
- 2 A plant in a bottle terrarium is 8 cm tall on day 1 and 11 cm tall on day 28. What is the plant's growth in centimeters, and what is the percent change in height?
- 3 Two sealed bottle ecosystems are built the same way, but one is placed near a bright window and the other is placed in dim light. Explain how light level could affect plant growth, condensation, and oxygen production over 4 weeks.