Final answer:
True, Na+ and K+ do slowly leak through specific channels in the cell membrane, following their concentration gradients which helps maintain the resting membrane potential.
Step-by-step explanation:
The statement that Na+ and K+ leak slowly but continuously through leakage channels in the plasma membrane down their concentration gradient is True. While membranes are normally impermeable to Na+, leakage channels facilitate the slow movement of Na+ into the cells and K+ out of the cells. This passive transportation is down the ions' respective concentration gradients, meaning Na+ moves into the cell where its concentration is lower and K+ moves out of the cell where its concentration is higher, due to the diffusion process.
The existence of these leakage channels maintains the resting membrane potential, commonly measured at -70 mV across the cell membrane. This potential would be much lower if not for the action of these channels along with the Na+/K+ pump, which actively restores the ionic balance by moving Na+ out of and K+ into the cell, consuming ATP in the process. This system is essential for maintaining proper cellular function, including the generation of action potentials in nerve and muscle cells.