Name: ______Date: ______
Student Exploration: Plants and Snails Wet Lab
Vocabulary: bromthymol blue (BTB), indicator, interdependence
Prior Knowledge Questions (Do these BEFORE using the Gizmo.)
1. What important gas do we take in when we breathe?
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2. Why don’t we run out of the important gases that we need to stay alive?
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Gizmo Warm-up
In the Photosynthesis Lab, each of the test tubes contains water and a small amount of bromthymol blue (BTB). BTB is a chemical indicator. An indicator changes color when the chemicals in the water change.
1. Add 1-2 drops of bomthymol blue to 15 mL of water in a test tube. Gently blow into the tube using a straw until it changes color. What color did it change to? Keep blowing, what color did it change to next?
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2. When the water changed yellow, it was because which gas was most common?
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When the water was blue, which gas was most common? ______
What does it tell you when the water is green? ______
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Activity A: Gases In & Gases Out
Question: What gases do plants and animals take in and what do they give off?
1. Place a sprig of elodea in the test tube with the yellow solution and insert a cork into the top. Expose the container to sunlight (or a bright lamp) for about 20 minutes.
A. What color(s) did the solution turn? Why?
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Place another sprig of elodea in a second test tube with 15 mL of water. Add 1-2 drops of
BTB. Cover this test tube with aluminum foil and let it sit for about 20 minutes.
B. What color(s) did the solution turn this time? Why?
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2. Analyze: Study your data on gases given off by plants.
A. What gas do plants give off in the light? ______
B. What gas do plants give off in the dark? ______
C. How is it possible that plants can be giving off both CO2 and O2?
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3. Analyze: Study your data on gases given off by animals.
A. What gas do animals give off in the light? ______
B. How about in the dark? ______
C. How do these results compare to your plant results? ______
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4. Extend your thinking: What do you think would happen if plants and animals were put in the same test tube? Explain your thinking.
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Activity B: Interdepence
Question: How do plants and animals depend on each other?
1. Observe: Put one sprig of Elodea and one snail in a test tube with 15 mL of water. Add 1-2 drops of BTB. Place it under the lights for about 20 minutes.
A. Predict what color you think the water will be after about 20 minutes.
B. Did the color of the water in the tube change? Explain your answer in terms of O2 and CO2 levels? ______
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2. Predict: Put another sprig of elodea and one snail in a test tube with a 15 mL of water. Add 1-2 drops of BTB. Wrap this test tube in aluminum foil and let it sit for about 20 minutes.
A. Predict what color you think the water will be after about 20 minutes.
B. Did the color of the water in the tube change? Explain your answer in terms of O2 and
CO2 levels?
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3. Generalize: Describe how plants and animals each contribute to the survival of the other.
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4. This type of cooperative relationship is called interdependence. Using the above question as your guide, what does interdependence mean?
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Application Review
Use the two graphs below to answer the following questions.
Earth’s Early Atmosphere Earth’s Current Atmosphere
1. Analyze the two graphs. What is the dependent variable on both graphs?
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What is the independent variable on both graphs? (Hint: Don’t look at the X-axis this time!)
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2. Based on the data from the graph on the left, did photosynthetic or non-photosynthetic organisms evolve first? How can you tell?
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