USA Biology Olympiad (USABO) Practice Exam

If an amoeba has different (+) and (-) ion concentrations compared to its environment, what can be inferred?

1. Only one type of ion is present

2. Other ions are also involved

3. The amoeba cannot survive in that environment

4. Ion concentrations will equalize over time

The correct answer is: Other ions are also involved

The presence of different positive and negative ion concentrations in the amoeba compared to its surrounding environment indicates that there are likely various ions involved in maintaining the amoeba's internal balance. This discrepancy suggests that multiple ions are interacting, influencing the osmotic pressure and cellular functions. In a biological context, cells often rely on a variety of ions—such as sodium, potassium, calcium, chloride, and bicarbonate—for maintaining various physiological processes, including membrane potential, nerve impulse transmission, and muscle contraction. If an amoeba's internal ion concentrations differ from its environment, it implies active transport mechanisms are at work, which regulate the levels of several ions simultaneously. The other options either oversimplify the situation by suggesting there is only one type of ion or imply a condition that might not apply universally, such as the amoeba's survival or the inevitability of equalization of ion concentrations, which might not happen due to the amoeba's mechanisms for maintaining homeostasis.