The cellular process known as the sodium-potassium pump was discovered in the 1950s by Jens Christian Skou, a Danish scientist. This process is a form of active transport that moves three sodium ions outside a cell for every two potassium ions it moves into the cell. Which best explains why energy is needed for active transport?

 Energy is needed for active transport because active transport processes like the sodium-potassium pump work against the concentration gradient. In this particular example, the pump moves three sodium ions out of the cell for every two potassium ions it moves into the cell. This means that the pump is moving sodium ions from an area of low concentration inside the cell to an area of high concentration outside the cell, and potassium ions from an area of low concentration outside the cell to an area of high concentration inside the cell.

To understand why energy is needed, think of it like moving objects up a hill. It requires energy to move objects uphill against gravity, just like it requires energy to move ions against their concentration gradients in active transport. Without the input of energy, the ions would naturally move down their concentration gradients, with sodium ions moving into the cell and potassium ions moving out of the cell.

The energy needed for active transport is provided by a molecule called adenosine triphosphate (ATP). ATP is a molecule that stores and carries energy in cells. When ATP is broken down into adenosine diphosphate (ADP) and inorganic phosphate (Pi), energy is released that can be used for various cellular processes, including active transport. The energy released from ATP is used by the sodium-potassium pump to move the sodium and potassium ions against their concentration gradient.