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 to the outside of a cell for every two potassium ions that it moves into the cell. which of these best explains why energy is needed for active transport?
a. ions are moved against the concentration gradient.
b. ions are negatively charged.
c. ions are attached to large proteins.
d. ions are trapped inside the plasma membrane.

A. Ions are moved against the concentration gradient.

Explanation:

Active transport is a process of transport of substances that moves the substances against their concentration gradient. This means that a substance is being moved from the region of its lower concentration to the region of its higher concentration.

To move the substances against their concentration gradients, cells spend metabolic energy. Therefore, active transport always requires energy to move the substances. Since sodium-potassium pump uses energy to move sodium and potassium ions, it is moving these ions against the concentration gradient.

the answer is d. embryo