Final answer:
Blocking K+ leak channels causes depolarization of the cell by preventing K+ from exiting the cell and hindering the repolarization process necessary for returning to the resting membrane potential.
Step-by-step explanation:
If K+ leak channels are blocked, the effect on the cell would be depolarization. Typically, during the repolarization phase of an action potential, K+ ions leave the cell, which helps the cell return to its resting membrane potential. With K+ channels blocked, K+ cannot exit the cell as usual, leading to less negative charge inside the cell and thus creating a state of depolarization. This can halt the cell's ability to return to its resting state and prepare for subsequent action potentials, as the normal repolarization process is disrupted.
Please note that hyperpolarization occurs when there is an excessive exit of K+ ions outside the cell during an action potential, making the cell more negative than its resting potential. In this scenario, because K+ ions cannot leave the cell, hyperpolarization would not occur as a result of blocked K+ leak channels.
In sum, the cell would remain in a partly depolarized state, which can affect the cell's excitability and the generation of subsequent action potentials.