In cell membrane transport, the movement of substances across a membrane from a region of lower concentration to a region of higher concentration, using cellular energy, is known as what?

Introduction / Context:
Cells constantly move substances across their plasma membranes to maintain internal conditions that are different from the external environment. Some movements occur naturally from high concentration to low concentration, while others require the cell to move substances in the opposite direction, against the concentration gradient. This question asks you to identify the correct term for the energy requiring movement of substances from low concentration to high concentration across a membrane.

Given Data / Assumptions:

• The movement described is against the concentration gradient, from lower to higher concentration.
• The process requires cellular energy, usually in the form of ATP.
• Options include active transport, diffusion, osmosis, passive transport, and facilitated diffusion.
• We assume a basic understanding of membrane transport processes.

Concept / Approach:
Movement of molecules from an area of higher concentration to lower concentration is called diffusion and does not require energy; it is a passive process. Osmosis is a special case of diffusion that involves water molecules. Passive transport includes simple diffusion and facilitated diffusion, where substances move down their concentration gradient through channels or carrier proteins. In contrast, when a cell must move ions or molecules against their concentration gradient, it uses energy from ATP and specific carrier proteins called pumps. This energy dependent movement is known as active transport.

Step-by-Step Solution:
Step 1: Note that the question specifies movement against the concentration gradient, which means from low concentration to high concentration. Step 2: Recall that passive processes like diffusion and osmosis do not require energy and move substances down their gradients only. Step 3: Recognize that moving substances against the gradient requires the input of energy, most often ATP. Step 4: Remember that this energy dependent transport is referred to as active transport. Step 5: Select active transport as the correct term for this process and reject the options that refer to passive processes.

Verification / Alternative check:
A classic example is the sodium potassium pump (Na+ / K+ ATPase) in animal cell membranes. It uses ATP to pump sodium ions out of the cell and potassium ions into the cell, both against their concentration gradients. This pump is essential for maintaining membrane potential and normal cell function. Because this process clearly moves ions from low to high concentration using ATP, it is described as active transport. Comparing this example to the definition in the question confirms that active transport is the correct answer.

Why Other Options Are Wrong:
Simple diffusion down the concentration gradient: This is movement from high concentration to low concentration without energy input, the opposite of what the question describes. Osmosis, the diffusion of water across a semipermeable membrane: Osmosis is a type of passive diffusion involving water, not an energy requiring process against a gradient for solutes. Passive transport without any energy expenditure: By definition, passive transport does not move substances against their concentration gradients. Facilitated diffusion through channel proteins only: Facilitated diffusion still moves substances down their gradients, even though proteins are involved, so it remains passive, not active.

Common Pitfalls:
Students sometimes confuse facilitated diffusion with active transport because both use membrane proteins. However, the key difference is the direction relative to the concentration gradient and whether energy is used. Facilitated diffusion helps substances move down the gradient without energy, whereas active transport pumps substances against the gradient using ATP. Keeping this distinction clear prevents errors in questions about membrane transport mechanisms.

Final Answer:
The movement of substances across a membrane from lower to higher concentration using cellular energy is called Active transport across the membrane using ATP.