Final answer:
Glucose molecules would move into the cell from a higher concentration outside to reach equilibrium via passive transport. Without a gradient, there is no net flow, but active transport mechanisms like symporters can move glucose against the gradient using energy.
Step-by-step explanation:
If glucose molecules outside a cell have higher energy than those inside the cell, then those molecules would move into the cells. As glucose molecules attempt to reach equilibrium, they will naturally move down their concentration gradient; from an area of higher concentration to an area of lower concentration, until the concentrations are equal on both sides of the cell membrane. This process does not require energy from the cell and is known as passive transport. If glucose transport proteins are present in the cell membrane, glucose would still follow the same rule and flow into the cell where it is less concentrated.
However, if the concentration of glucose was equal inside and outside of the cell, there would not be a net flow of glucose across the cell membrane because there is no gradient to drive diffusion. Only if there are mechanisms in place, like active transport or cotransport systems, would there be movement of glucose against the gradient, which would require energy in the form of ATP.
For example, symporters are secondary active transporters that can move substances against their concentration gradients using the energy from the flow of another substance down its gradient. The sodium-glucose symporter is an example of this, using the energy from sodium ions entering the cell to transport glucose into the cell, even against its concentration gradient.