1. The researchers chose a concentration of 0.3 mM IAA as the working concentration for any additional studies instead of 1 mM or 2 mM. What is the likely reason for this?
A) The lower concentration of IAA gave the largest Na+ response.
B) Higher concentrations induced significant cytotoxicity.
C) The solubility of IAA was not high enough.
D) The researchers were trying to mimic control conditions as closely as possible.
The correct answer is B.
Rationale: This question requires you to apply your knowledge of cytotoxicity and cell lysis to the experimental design described in the passage. You must understand that an experiment with IAA levels cytotoxic to cells would not lend itself to understanding the role of glycolysis in establishing ion concentration gradients. When compared to control conditions, under cytotoxic IAA levels the membrane integrity of cells will be compromised leading to cell lysis. Therefore, the researchers chose a concentration of 0.3 mM IAA as the working concentration for their experiments to reduce the chance of cell lysis.