Final answer:
True, polar molecules use active transport to move against their concentration gradient across a membrane, relying on energy-consuming membrane proteins to assist in their movement.
Step-by-step explanation:
The statement presented is true: Polar molecules that need to be transported across the membrane against their concentration gradient use active transport. This is because these molecules cannot pass easily through the cell membrane due to their polarity and require assistance from membrane proteins that consume energy, often in the form of ATP (adenosine triphosphate).
Active transport mechanisms are crucial when a substance must move into or out of a cell against its concentration gradient, requiring an input of energy to do so. In biological systems, this process is managed by specialized protein complexes such as pumps and transporters that bind the polar molecules and expend energy to carry them across the plasma membrane, hence maintaining essential concentrations of various solutes necessary for cellular function.
This energy-dependent transportation is in contrast to passive transport, where substances flow from an area of higher concentration to an area of lower concentration without the need for cellular energy. Examples of passive transport include simple diffusion and facilitated diffusion, the latter involving specific protein channels to allow the movement of substances down their concentration gradient without energy input.