The heartbeats of the heart are controlled by the sinoatrial node also known as the pacemaker of the heart. The impulse is generated in the conducting cells of the pacemaker as a result of the movement of sodium, potassium and calcium ions.
The sodium channels allow the movement of sodium into the cell which depolarizes the membrane from -60mv to -40 mv. At this point, the calcium gated channels open which allow the entry of the calcium in the cell which depolarizes the cell up to +5mv.
At this point, the potassium channels open which allows the potassium ions to move out of the cell. This repolarizes the cell and hence the cycle again begins. Reducing the permeability of the potassium ions help generate the autorhythmicity due to repolarization and thus is the correct answer.
Producing and exporting organs in the plant (typically mature leaves) are known as sources, while non-photosynthetic organs (fruits, roots and tubers) and immature leaves are known as sinks.
