Question

the na+/k+-atpase transports sodium ions (na+) and potassium ions (k+) across the cell membrane from low concentration to high concentration while breaking down atp into adp and a phosphate group. which statements about the na+/k+-atpase are accurate?
na+/k+-atpase moves na+ and k+ ions by passive transport.
breakdown of atp by na+/k+-atpase is a spontaneous process.
the coupling of na+ and k+ transport with breakdown of atp is an overall spontaneous process.
transporting na+ and k+ against their respective concentration gradients is a nonspontaneous process.

Explanation:

• Passive transport moves substances down their concentration gradient without energy. Since \(Na^{+}/K^{+}\)-ATPase moves ions against the concentration gradient (low to high) and uses ATP, it is not passive transport. So the first statement is incorrect.
• The breakdown of ATP (\(ATP

ightarrow ADP + P_{i}\)) is a spontaneous reaction (\(\Delta G<0\)) as it releases energy.

• The overall process (ion transport + ATP breakdown) is spontaneous. The non - spontaneous ion transport (\(\Delta G>0\)) is coupled with the spontaneous ATP breakdown (\(\Delta G<0\)), and the sum \(\Delta G_{total}=\Delta G_{transport}+\Delta G_{ATP\ breakdown}<0\) (because \(|\Delta G_{ATP\ breakdown}|>|\Delta G_{transport}|\)).
• Transporting ions against their concentration gradient (\(\Delta G>0\)) is a non - spontaneous process.

Answer:

• Second statement: Breakdown of ATP by \(Na^{+}/K^{+}\)-ATPase is a spontaneous process.
• Third statement: The coupling of \(Na^{+}\) and \(K^{+}\) transport with breakdown of ATP is an overall spontaneous process.
• Fourth statement: Transporting \(Na^{+}\) and \(K^{+}\) against their respective concentration gradients is a nonspontaneous process.