<span>The correct answer is D. Active transport is the movement of a substance across a cell membrane against its concentration gradient (from low to high concentration instead of high to low, which is what naturally occurs as diffusion). </span>
The correct option is D. When it comes to movement of particles in an out of cells, there are two basic types of transportation, these are passive and active transportation. The passive transportation of particles does not require the use of energy while the active transport system requires the use of energy in the form of ATP. From the diagram given in the question, it can be seen that energy is involved in the process. Energy is mainly needed to move the particles against the concentration gradient since the inside of the cell is highly concentrated while the outside has low concentration. <span />
