Teach lesson
Cellular Respiration: how activation changes CO2 accumulation
Students use the Cellular Respiration remote lab to compare CO2 accumulation from water-activated, acid-activated, and dry seeds, then calculate concentration-change rates from real readings.
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Learning Outcomes
Explain why CO2 concentration in a closed seed chamber can be evidence of cellular respiration.
Use the Cellular Respiration remote lab to record CO2 concentration readings for seed activation conditions.
Calculate average CO2 concentration-change rate from CO2 concentration change over 240 seconds.
Compare water-activated, acid-activated, and dry seeds using evidence rather than a single final reading.
Identify controlled variables and explain why seed color is not the investigated variable in this lab.
Write a bounded claim that connects activation, metabolism, evidence quality, and uncertainty.
Student activity preview
Activity Content
Preview only. In a class session, students can fill in responses and submit their work to the teacher.
Frame the biological question
8 min
A dry seed can look like it is doing nothing, but it is not the same as a dead object. Many seeds stay in a low-activity state until conditions such as water make germination possible. When metabolism restarts, cells need usable energy, and aerobic respiration is one process that releases that energy from stored food.
One detectable product of aerobic respiration is carbon dioxide. In this lab, seeds are sealed in a chamber and a CO2 sensor records how CO2 concentration changes over time. The lab does not show a plant growing during the lesson; it uses CO2 change as evidence that seed metabolism is more or less active under different activation conditions.
Cellular respiration setup
The real lab uses a sealed seed chamber and a CO2 sensor. The comparison is fair only if the chamber, sensor, seed type, and run time stay the same.
Activation conditions
The real variable is seed activation: water pH 7, acetic acid pH 5, or dry/not activated. Seed color is not the investigated variable in this investigation.
Aerobic respiration evidence
\mathrm{C_6H_{12}O_6} + 6O_2 \rightarrow 6CO_2 + 6H_2O
Aerobic respiration releases usable energy for the cell.
Why can CO2 inside the chamber be used as evidence that the seeds are respiring?
Predict which condition will have the highest CO2 concentration-change rate: water-activated seeds, acid-activated seeds, or dry/not-activated seeds. Explain your prediction in 3-4 sentences using dormancy, water uptake, or activation.
Plan a fair comparison
8 min
The lab offers three activation conditions. You will compare them using the same observation times and the same rate calculation. Plan to collect one row for each condition and to label how each row was obtained. In the compact route, your group may run one assigned condition live and use teacher-provided rows for the other two; the row labels must make that clear.
What is the independent variable in this investigation?
Collect CO2 concentration readings
22 min
Open the lab from this activity and collect CO2 concentration readings at fixed times. Use the CO2 concentration display or graph that appears in the TEACH-launched lab, and keep the same reading times for each condition. The 60, 120, and 180 s readings are part of the evidence record, not optional extras; they help you check the trend and make a graph if your teacher assigns one.
Open Cellular Respiration
Open the Cellular Respiration lab.
In the full route, run Activated in water (pH 7), Activated in acetic acid (pH 5), and Not activated / not soaked. Record CO2 concentration at 0, 60, 120, 180, and 240 s for each condition.
In the compact route, run only your assigned condition live, then use class or teacher-provided rows for the other two conditions.
For each row, label the evidence origin, such as live lab reading, class shared row, or teacher-provided row.
Do not use seed color as a variable; this lab investigates activation condition.
CO2 concentration readings and average rate
Complete at least one row for each activation condition. Use CO2 concentration in ppm and rate in ppm/s. Rate = (CO2 concentration at 240 s - CO2 concentration at 0 s) / 240 s.
| Condition | Replicate/evidence origin | CO2 concentration at 0 s ppm | CO2 concentration at 60 s ppm | CO2 concentration at 120 s ppm | CO2 concentration at 180 s ppm | CO2 concentration at 240 s ppm | Delta CO2 concentration ppm | Average rate ppm/s | Notes or uncertainty |
|---|---|---|---|---|---|---|---|---|---|
Optional evidence file or graph
Optional if your teacher asks for a separate file: attach or reference one useful graph, spreadsheet/table, screenshot set, or short calculation sheet. If your evidence is only the TEACH data table, you do not need a separate file.
Analyze rate, not just final CO2
14 min
Final CO2 concentration is useful, but concentration-change rate is the stronger comparison because it describes how fast CO2 accumulates.
Here C means CO₂ concentration in ppm, not partial pressure. Calculate ΔC/Δt in ppm/s: the net rate at which CO₂ concentration changes in the chamber. With comparable seed amounts, chamber volume, temperature and timing, this is a proxy for comparing respiration. It is not a rate in mol/s; a small negative value can reflect background drift or measurement variation and does not mean negative respiration.
Average CO2 concentration-change rate
\text{average rate}=\frac{\text{CO2 concentration at 240 s}-\text{CO2 concentration at 0 s}}{240\ \text{s}}
From your table, calculate the average CO2 concentration-change rate for the water-activated pH 7 row. Enter the rate in ppm/s and show your subtraction and division.
First name the fastest row in your table. Then calculate how many times faster it is than the pH 5 acid-activated row. Enter the ratio and explain which two rows you compared.
Identify the dependent variable and two controlled variables. In a separate sentence, explain why seed color is not a valid variable for this investigation.
Optional class summary table
Teacher-managed class table for pooling representative rates. Use it after student submission if the class used different replicates or teacher-provided reference rows.
| Condition | Class mean or representative rate ppm/s | Range or notes |
|---|---|---|
Make a careful biological claim
10 min
The conclusion should connect the numbers to biology without claiming more than this lab can show.
Name two uncertainty sources or evidence limits in this lab, such as manual readings, reading-time choice, or replicate variation. For each one, explain how it could affect your rate comparison or final claim.
Which claim would overstate what this lab proves?
Write a final claim-evidence-reasoning answer. Include:
- which condition had the highest rate;
- at least two numerical rate or CO2 concentration pieces of evidence;
- how activation or imbibition affects seed metabolism;
- one uncertainty or limitation.
Optional extension: replicates and fairness
15 min
Use this only if your teacher assigns the longer route.
If you repeat one condition and get a different final CO2 concentration value, how should you decide whether the overall conclusion is still reliable? Mention the pattern across rates, how large the difference is, and whether the same condition remains highest.
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