Effect of Water-Soluble Pollutants on Membrane Permeability
Treatment Group Treatment Solution (percent by volume) Mean Absorbance of 460 nm Light (n=5) 2× Standard Error of the Mean (2×SEM)
I

70% isopropanol; 30% water

0.164 0.032
II 90% isopropanol; 10% water 0.125 0.100
III

50% acetone; 50% water

0.215 0.034
IV

70% acetone; 30% water

0.274 0.018
V 100% water 0.095 0.004

A student formulated a hypothesis that water-soluble pollutants damage living organisms by increasing the permeability of cellular membranes. To test the hypothesis, the student investigated the effect of isopropanol and acetone on beet root cells. The vacuoles of beet root cells contain large amounts of betacyanin, a water-soluble pigment that is released into the extracellular environment as a result of increased membrane permeability.

The student prepared identical samples of beet root tissue and incubated each sample for 15 minutes in the specific solution for that group. At the end of the incubation period, the student measured the absorbance of 460 nm light for each sample. A greater concentration of betacyanin in the solution surrounding the beet root cells results in a greater absorbance of 460 nm light. The results of the experiment are shown in the table above.

Based on the data from the investigation, which of the following is the best scientific question about organisms living in water that is polluted with organic solvents?

Question

Effect of Water-Soluble Pollutants on Membrane Permeability
Treatment Group	Treatment Solution (percent by volume)	Mean Absorbance of 460 nm Light (n=5)	2× Standard Error of the Mean (2×SEM)
I

70% isopropanol; 30% water

0.164	0.032
II	90% isopropanol; 10% water	0.125	0.100
III

50% acetone; 50% water

0.215	0.034
IV

70% acetone; 30% water

0.274	0.018
V	100% water	0.095	0.004

A student formulated a hypothesis that water-soluble pollutants damage living organisms by increasing the permeability of cellular membranes. To test the hypothesis, the student investigated the effect of isopropanol and acetone on beet root cells. The vacuoles of beet root cells contain large amounts of betacyanin, a water-soluble pigment that is released into the extracellular environment as a result of increased membrane permeability.

The student prepared identical samples of beet root tissue and incubated each sample for 15 minutes in the specific solution for that group. At the end of the incubation period, the student measured the absorbance of 460 nm light for each sample. A greater concentration of betacyanin in the solution surrounding the beet root cells results in a greater absorbance of 460 nm light. The results of the experiment are shown in the table above.

Based on the data from the investigation, which of the following is the best scientific question about organisms living in water that is polluted with organic solvents?

BlackTom AI · Accepted Answer

Increased membrane permeability causes intracellular, water-soluble molecules (like betacyanin) to leak into the environment; measuring absorbance of the bathing solution quantifies that leakage and indicates membrane damage.

1) Relevant knowledge points and concepts
- Cellular membranes regulate solute movement; disruption increases permeability and causes loss of cytoplasmic/vacuolar contents.
- Betacyanin is water-soluble and confined to beet vacuoles when membranes are intact; higher absorbance at 460 nm means more leakage and greater membrane damage.
- A good scientific question is testable, directly linked to the hypothesis and measurable outcomes, and not a policy or purely speculative question.

2) Step-by-step reasoning using the table
- Control (100% water, Group V) absorbance = 0.095 (2×SEM = 0.004).
- Solvent treatments show higher absorbance: 70% acetone (Group IV) = 0.274 (2×SEM = 0.018), 50% acetone = 0.215 (2×SEM = 0.034), 70% isopropanol = 0.164 (2×SEM = 0.032), 90% isopropanol = 0.125 (2×SEM = 0.100).
- These higher values indicate solvents increase membrane permeability relative to pure water.

3) Intermediate calculations (comparisons)
- Difference between 70% acetone and water: 0.274 − 0.095 = 0.179. Combined 2×SEM roughly ≤ 0.018 + 0.004 = 0.022, so the difference (0.179) greatly exceeds measurement uncertainty.
- Difference between 90% isopropanol and water: 0.125 − 0.095 = 0.030. Combined 2×SEM ≈ 0.100 + 0.004 = 0.104, so this small difference is within uncertainty and may not be significant.

4) Why the correct answer is correct
- "Will organisms living in polluted environments exhibit detrimental effects from an increased permeability of their cellular membranes?" directly connects the observed solvent-induced membrane leakage to organismal consequences (detrimental effects). It is scientific and testable (measure survival, growth, physiological function under solvent exposure) and follows logically from the experimental evidence showing increased permeability.

5) Why the other options are incorrect
- "Should governments..." is a policy question, not a testable scientific hypothesis derived from the experiment.
- "Do organisms without pigments have a selective advantage..." is speculative and not tied to membrane permeability; the experiment measures leakage, not selection or pigment-based advantage.
- "Will organic solvents become incorporated into cell membranes..." is a mechanistic biochemistry question that could be tested, but it is not the primary organism-level consequence illustrated by the betacyanin leakage data; it asks a different mechanism rather than the direct effect measured.

6) Conclusion
The best scientific question is: "Will organisms living in polluted environments exhibit detrimental effects from an increased permeability of their cellular membranes?" This matches the provided correct answer.

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