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Tracing the Source of Oxygen in a Leaf Model 4 questions
Tracing the Source of Oxygen in a Leaf Model
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A classroom simulation traces oxygen atoms during photosynthesis. It can mark oxygen atoms with a stable isotope label without changing their modeled chemistry. In each run only one starting substance carries the label. The model does not let the label move between water and carbon dioxide before oxygen gas forms.
| Run | Starting substance with labeled oxygen atoms | Label detected in released O2? |
|---|---|---|
| J | Water | Yes |
| K | Carbon dioxide | No |
Question 1
Which source of oxygen atoms in the released oxygen gas is supported by the two runs?
- Water
- Carbon dioxide
- Both substances contribute equally.
- Neither substance contributes.
Question 2
Explain why a run with both starting substances labeled would be less useful for deciding which one supplies the oxygen atoms.
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A student notices that the carbon dioxide in K still contains oxygen atoms. The student concludes that oxygen atoms in carbon dioxide must be released as O2 because photosynthesis consumes carbon dioxide.
Question 3
Use the label result in K to evaluate the student’s conclusion.
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Question 4
Describe a control run that checks whether the detector reports the label even when none was added.
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