Angela's Tools · Chapter 7 · Global Cycles of Matter
Worksheet 5 of 10
Carbon by the Hour, Nitrogen by the Week: Two Teaching Datasets
Learning target: I can graph and calculate from data about a sealed terrarium and a fertilized pond to show that matter moves between reservoirs at measurable rates without being created or destroyed.
Data and graphingAbout 45 minIndividual
MS-LS2-3 · practiceMS-LS2-4 · practiceMS-LS1-6 · supports
data analysisindependent practice
NameDatePeriod
Directions
This sheet has three parts. Part A and Part B use teaching datasets: the numbers were invented to be realistic and were not measured in a real lab. Part C uses real reference values. Graph with a ruler, show every calculation with units, and when a question asks where matter went, name the reservoir it moved to.
You will need: This worksheet, Pencil, Ruler, Calculator (optional)
Part A: Carbon dioxide inside a sealed terrarium
A class sealed a clear 20-liter container holding moist soil, three small plants and a carbon dioxide sensor. A lamp on a timer lit the container from 6:00 a.m. to 6:00 p.m.; the rest of the time it was dark. The sensor reported carbon dioxide in parts per million (ppm) every two hours. Nothing entered or left the container except light and heat.
Carbon dioxide in the sealed terrarium over 24 hours (teaching dataset)
Simulated teaching dataset: the numbers are invented to be realistic, not measured.
| Clock time | Hours since start | Lamp | Carbon dioxide (ppm) |
|---|
| 6:00 a.m. | 0 | on | 900 |
| 8:00 a.m. | 2 | on | 810 |
| 10:00 a.m. | 4 | on | 725 |
| 12:00 noon | 6 | on | 640 |
| 2:00 p.m. | 8 | on | 560 |
| 4:00 p.m. | 10 | on | 480 |
| 6:00 p.m. | 12 | off | 400 |
| 8:00 p.m. | 14 | off | 485 |
| 10:00 p.m. | 16 | off | 565 |
| 12:00 midnight | 18 | off | 645 |
| 2:00 a.m. | 20 | off | 725 |
| 4:00 a.m. | 22 | off | 805 |
| 6:00 a.m. | 24 | on | 880 |
Simulated data for teaching. Realistic for a small planted container with a classroom sensor.
1.Calculate the total drop in carbon dioxide while the lamp was on (hour 0 to hour 12), then the average rate of change in ppm per hour. Show your work.
2.Calculate the total rise in carbon dioxide while the lamp was off (hour 12 to hour 24), then the average rate in ppm per hour. Show your work.
3.What was the net change in carbon dioxide over the full 24 hours (hour 24 minus hour 0)? Is it positive or negative, and what does the sign tell you about where some carbon ended up?
4.Describe the shape of your graph. Name the process that dominates during the lit hours and the process that continues during the dark hours, and explain how the graph shows that the second process never actually stopped during the day.
5.The container was sealed. During the lit hours, 500 ppm worth of carbon dioxide 'disappeared' from the air inside. Where was that carbon at 6:00 p.m.? Use the idea of reservoirs and the law of conservation of matter in your answer.
Part B: Nitrate and algae in a pond after a fertilizer spill
Heavy rain washed nitrate fertilizer off a field into a farm pond during week 1. A student measured nitrate in the water and estimated the percent of the surface covered by algae every week for eight weeks.
Pond nitrate and algae cover after a fertilizer spill (teaching dataset)
Simulated teaching dataset: the numbers are invented to be realistic, not measured.
| Week | Nitrate (mg/L) | Algae cover (% of surface) |
|---|
| 0 | 0.4 | 5 |
| 1 | 6.2 | 8 |
| 2 | 5.1 | 20 |
| 3 | 3.6 | 45 |
| 4 | 2.0 | 70 |
| 5 | 1.1 | 85 |
| 6 | 0.7 | 80 |
| 7 | 0.5 | 60 |
| 8 | 0.4 | 35 |
Simulated data for teaching. Patterns are realistic for a small warm pond; the numbers were not measured at a real site.
6.By how much did nitrate fall from week 1 to week 5? What was the average fall per week over those four weeks? Show your work.
7.Describe the relationship between nitrate and algae cover from week 1 to week 5. Where did the nitrogen that left the water go? Name the reservoir.
8.From week 5 to week 8 the algae cover falls but nitrate stays low. Explain why the algae decline, and predict which process is now moving nitrogen and what reservoir it is moving it to.
Part C: Real reference values
Composition of dry air near the ground (real rounded values)
| Gas | Share of air by volume |
|---|
| Nitrogen gas | 78% |
| Oxygen gas | 21% |
| Argon | 0.9% |
| Carbon dioxide | about 0.04% |
| All other gases | less than 0.1% |
Carbon dioxide is given as 'about' because it rises every year; it passed 0.04% (400 ppm) in the 2010s.
9.Air is 78 percent nitrogen, yet the pond in Part B only bloomed when nitrate was added. Use the table and what you know about nitrogen fixation to explain why the air's huge nitrogen reservoir did not cause the bloom.
10.Both datasets show matter leaving one reservoir and appearing in another. Using at least one number from each dataset, explain how the two datasets together support the law of conservation of matter.
Rate means change divided by time
For every rate question: (1) write the later value minus the earlier value to get the change, with units (ppm or mg/L); (2) write the number of hours or weeks between them; (3) divide the change by the time. Keep the sign: a negative change means the amount went down. Example with made-up numbers: 650 ppm − 710 ppm = −60 ppm over 3 hours gives −20 ppm per hour.
A second terrarium, no plants
Predict the 24-hour carbon dioxide graph for an identical sealed container holding the same moist soil but no plants. Sketch it on the same axes as your Part A graph, explain the difference in shape, and then describe how you could use the two containers together to measure how much carbon dioxide the plants alone take in per hour. State what you would have to keep the same in both containers.