A substance moving across a membrane against a concentration gradient is moving by                   . a. passive transport; b. osmosis; c. facilitated diffusion; d. active transport; e. diffusion

Key Concepts

Concentration Gradient

A concentration gradient refers to the difference in the concentration of a substance across a space or membrane. Substances tend to move from areas of higher concentration to areas of lower concentration, which is a fundamental principle in understanding how molecules move within biological systems.

Active Transport

Active transport is the process by which substances move across a cell membrane against their concentration gradient, requiring energy, typically in the form of ATP. This mechanism is crucial for maintaining cellular homeostasis and allowing cells to uptake necessary nutrients even when they are in lower concentrations outside the cell.

Passive Transport

Passive transport is the movement of substances across a cell membrane without the use of energy, occurring along the concentration gradient. This includes processes like diffusion and osmosis, where molecules move from areas of higher concentration to lower concentration until equilibrium is reached.