Analyze data
Contractile vacuoles and salt
- Unit 2
- 4 points
- About 10 minutes
You can use a calculator on this question, just like on exam day.
A short question with data in a table or graph. You describe what the data show, use the data to judge a hypothesis, and explain how the results connect to biology you know. On the exam: Question 6 of 6 in Section II; about 10 minutes suggested.
The question and its sources
Paramecium is a single-celled protist that lives in fresh water. It has no cell wall. It has contractile vacuoles that collect excess water from the cytoplasm and pump it out of the cell, using ATP.
Investigation
Researchers moved Paramecium from pond water into solutions with different concentrations of NaCl. After 30 minutes, they counted how many times a contractile vacuole emptied (contracted) per minute in each of 10 cells per solution. In the 75 mM solution, the cells did not change in volume during the 30 minutes.
Source: Hypothetical study
Table 1. Contractile vacuole contractions per minute, mean ± 2SE
| NaCl concentration (mM) | Contractions per minute |
|---|---|
| 0 | 9.6 ± 0.8 |
| 10 | 7.1 ± 0.7 |
| 25 | 4.4 ± 0.6 |
| 50 | 1.8 ± 0.4 |
| 75 | 0.6 ± 0.3 |
Source: Hypothetical data
Suggested time: 10 minutes
Your answers are saved in this browser as you type.
Part (a)
1 pointBased on Table 1, describe the relationship between NaCl concentration and the rate of contractile vacuole contraction.
0 / 2,500 characters
Part (b)
1 pointCalculate the percent decrease in the rate of contraction at 50 mM NaCl compared with 0 mM NaCl.
0 / 2,500 characters
Part (c)
1 pointA researcher hypothesizes that less water enters a Paramecium by osmosis as the NaCl concentration outside the cell increases. Use the data to evaluate this hypothesis.
0 / 2,500 characters
Part (d)
1 pointExplain why a Paramecium in pond water would swell and burst if its contractile vacuoles stopped working, while a plant cell placed in pond water does not burst.
0 / 2,500 characters
Checking scoring…
Scoring it yourself shows you the rubric, examples and a model answer. Try writing your answer first.