USA Biology Olympiad (USABO) Practice Exam

The differences in K+ and Na+ concentrations inside and outside an amoeba suggest what?

1. Passive transport is occurring

2. Energy has been expended

3. Cell division is taking place

4. The amoeba is dead

The correct answer is: Energy has been expended

The significant differences in K+ (potassium) and Na+ (sodium) concentrations between the inside and outside of an amoeba indicate an active process of maintaining these gradients, which involves energy expenditure. In biological systems, cells typically maintain high concentrations of potassium ions inside and lower concentrations of sodium ions, which is contrary to their equilibrium states. This is achieved through the operation of the sodium-potassium pump, a type of active transport mechanism that uses ATP to move sodium ions out of the cell and potassium ions into the cell against their concentration gradients. The active transport of ions is crucial for various cellular functions, including maintaining membrane potential, driving secondary active transport processes, and facilitating cellular signaling. Thus, the observation of these ion concentration differences strongly suggests that energy in the form of ATP has been utilized to establish and maintain the necessary ion gradients for the amoeba's survival and function.