The question
Name: ______________________ Date: ____________ Potassium uptake by root tissue with and without oxygen (9 points)
Data table
Potassium uptake by root tissue with and without oxygen
Researchers grew barley seedlings in a solution without potassium, so their roots started with very little K⁺. They cut equal masses of young root tips and placed them in flasks of a solution containing 1.0 mM potassium ions (K⁺) at 25 °C. Air was bubbled through half of the flasks. Nitrogen gas was bubbled through the other half, which removes oxygen; without oxygen, the root cells make very little ATP. At each time, root samples were rinsed and the K⁺ they had taken up was measured. Values are means of 6 flasks ± 2 SE.
| Time (min) | Air bubbled (mean ± 2 SE) | Nitrogen bubbled (mean ± 2 SE) |
|---|---|---|
| 0 | 0.0 ± 0.0 | 0.0 ± 0.0 |
| 30 | 2.4 ± 0.3 | 0.6 ± 0.2 |
| 60 | 4.6 ± 0.4 | 0.8 ± 0.2 |
| 90 | 6.9 ± 0.5 | 0.9 ± 0.2 |
| 120 | 9.0 ± 0.6 | 0.9 ± 0.3 |
(a) (i) Identify the independent variable in this experiment. (ii) Justify keeping the K⁺ concentration of the solution at 1.0 mM in every flask. [2 points]
(b) Construct an appropriately labeled graph that shows the mean K⁺ taken up over time for both treatments, including error bars. [4 points]
(c) Determine whether the K⁺ taken up at 30 minutes differs between the two treatments. Use the error bars to justify your answer. [1 point]
(d) Root tissue contains about 0.9 mL of water per gram. Calculate the K⁺ concentration inside the air-bubbled roots at 120 minutes, in mM (µmol per mL), and use it to explain what kind of transport moved the K⁺. [1 point]
(e) At 120 minutes, nitrogen gas replaces the air in the air-bubbled flasks. Predict how the K⁺ content of those roots will change over the next hour, and justify your prediction. [1 point]