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The electrochemical gradient is the combination of both concentration and electrical gradients across a membrane.

In a cell, the plasma membrane acts as a selective barrier that keeps certain molecules and ions inside while keeping others out.

Because the plasma membrane is selectively permeable, ions such as sodium and potassium cannot freely diffuse across it. This leads to an uneven distribution of ions across the membrane.

Normally, there is more sodium outside a cell than inside. This creates a chemical or concentration gradient in which sodium would flow into the cell across the membrane if a pathway through channels or transporters were available.

The opposite is true for potassium, where there is a lower concentration of potassium ions outside the cell than inside.

This imbalance is maintained by selective permeability and active transport processes. However, ion concentration is not the only factor creating a gradient across the cell membrane.

The unequal distribution of charged ions across the membrane contributes to an electrical gradient. A higher concentration of potassium ions inside the cell, along with negatively charged proteins trapped within the cytoplasm, helps create the overall difference in charge across the membrane.