Which motion of particles across a membrane requires energy? from high concentration to low concentration from low concentration to high concentration with no concentration gradient through dynamic equilibrium

The correct answer is from low concentration to high concentration.

Energy is required when particles move from low concentration to high concentration. This process is called as active transport. Since movement of particles is against the concentration gradient, therefore, this process requires energy.

On the contrary, no energy is required when particles move from high to low concentration. Similarly, no energy is required when particles move through dynamic equlibrium.

Active transport is primarily divided into two types-

Primary active and secondary active transport.

In primary active transport, metabolic energy is used directly ( Example- hydrolysis of ATP)

In secondary active transport, energy is utilized by the motion of one particle along the concentration. This motion is coupled with the motion of another particle, which moves against the gradient.