Original Document / Student Handout
Purpose: In this lab you will observe the interaction of a snail and a water plant in a closed environment. The use of an indicator will allow you to observe the presence
Materials
Lately, I've had some difficulty getting aquarium snails, most fish shops find snails to be undesirable so they remove them or use chemicals to treat water. You may need to order aquarium snails from a biology company such as wards or carolina. Feeder guppies are a good substitute, but the cannot stay in small containers for very long and the BTB must be fairly diluted, the water color should only be a faint blue.
Experiment Set-Up
Each container will have water plus 4 drops of BTB,. Use the chart to set up your 8 containers. Label each container with the number and letter (example 2B) - I've listed the results you should expect from the experiment. Allow for flexibility here, conditions can cause results to vary dramatically. 4 drops is a guideline, it wil depend on the concentration of the solution and the size of the containers organisms are stored in. If using small baggies, 1 drop will probably be enough.
| Label | Set 1 - placed under strong light | Set 2 - placed in the dark |
| A | nothing (control) - no color change | nothing (control) - no color change |
| B | snail - color change to yellow | snail - color change to yellow |
| C | elodea stem with leaves - no color change, or possibily turns a darker blu as carbon is used | elodea stem with leaves - color change to yellow, respiration still occurs in plants in the dark, but no photosynthesis light reactions |
| D | snail + elodea - no color change, if balanced (varies depending on size of plant and animal) | snail + elodea - color change to darker yellow |
Data
Create a data table to record color changes in each of the containers. You will take data each day for three days. Also include a section of your data to analyze the health of the organisms.
Analysis - Use your data to answer the following questions.
1. Describe what happened in the experiment and propose an explanation for your observations. Plants use carbon dioxide for photosynthesis (if there is light), animals produces carbon dioxide which will turn the water yellow.
2. Explain why some of the jars changed colors while others did not. The ones that changed color show an extra amount of carbon dioxide (slightly acidic), which indicates that the organism within is producing CO2
3. Describe how plants and animals are dependent on each other. plants use carbon for photosynthesis, animal produce carbon dioxide
4. Make a prediction about what would happen in each the jars if they were left closed for a week. Most would die, if you had a balanced ecosystem with the snail and plant they could survive for a while, however other waste products would build up in the water and they would die eventually. Scientists have been trying to create a closed ecosystem, but have been unsuccessful.
See http://en.wikipedia.org/wiki/Biosphere_2 for more information on the biosphere.