SUBJECT: Science
GRADE: 7,8,9
TIME: 30 minutes
TYPE OF ACTIVITY: Demonstration or Student Investigation
TEACHING STRATEGY: Guided Discovery Expository
CONCEPTS: Acidification Indicator Solutions Gas Solubility
SKILLS: Observation Inference Experimentation

Objective: To understand the importance of providing a low Carbon Dioxide environment for the inhabitants of a spacecraft.

Materials: Several Guppies; a small aquarium or other container for the Guppies; a 100ml flask or glass; straws; Bromo-thymol-blue (BTB [optional]).

Have a student blow for about a minute into a glass of water through a straw. Introduce a Guppy to the glass. Observe the behavior of the Guppy for about 10 – 15 seconds. Remove the Guppy and place it in the original container. Review with students that BTB is an indicator for acid. Add two drops of BTB to a clean glass of water and have a student again blow through a straw into the water. Discuss with the students what main gas is exhaled when breathing. Relate the exhaled gas to the behavior of the Guppy in the water with the high CO2 content.
Teacher Note: The Guppy would not survive for long in the water with the high Carbon Dioxide content. The CD causes the water to turn acidic and the guppy may try to jump out or will swim violently around the glass trying to get out. If the Guppy is removed after only a short time in the bad water, it will survive. Do not wait more than 10 or 15 seconds though before replacing it in the good water. The BTB should turn to a light green, then yellow and eventually nearly clear as the concentration of CO2 gets higher in the water. The students should conclude that a high concentration of Carbon Dioxide is not conducive to keeping an animal alive.
Extension: See the next lesson to review a method to remove excess Carbon Dioxide from the air we exhale.

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