Final answer:
The specific percentage of the cell's energy used to take in potassium is not provided, but it is implied that a significant portion of cellular ATP is dedicated to the sodium-potassium pump, maintaining vital ion gradients.
Step-by-step explanation:
The sodium-potassium ATPase is a crucial membrane protein that uses cellular energy in the form of adenosine triphosphate (ATP) to maintain concentration gradients of sodium and potassium ions across the cell membrane. This process is vital for establishing the resting membrane potential and plays a fundamental role in various cellular activities.
The energy cost for transporting ions, specifically the energy used to take in potassium into the cell, is high because the ions are moved against their respective concentration gradients. The actual percent of the cell’s energy used solely for potassium ion intake is not specified here, but the provided information that one molecule of ATP relevant to this process releases 7.3 kcal/mol and it takes 2.1 kcal/mol to move one Na+ leads to the assumption that a significant portion of cellular ATP is consumed by this pump, given that potassium ions are taken into the cell constantly due to their high intracellular concentrations.