Definition

1. Noun:
   • A difference in the concentration of a substance across a distance: A "concentration gradient" is the gradual change in the concentration of a solute (a dissolved substance) from one area to another within a solution or across a membrane.
   • A driving force for molecular movement: It describes how the amount of a substance varies in space, creating a natural tendency for that substance to move from an area of higher concentration to an area of lower concentration.

Examples of Usage

• Noun:
  • Oxygen moves into the bloodstream down its concentration gradient. (Oxygen moves from the air in the lungs, where it is at a higher concentration, into the blood, where it is at a lower concentration.)
  • The experiment measured the ion flow along the established concentration gradient. (The experiment measured how ions moved from the side of the membrane with many ions to the side with fewer ions.)
  • Cells use energy to pump molecules against their concentration gradient. (Cells expend energy to move molecules from an area of low concentration to an area of high concentration, which is the opposite direction of natural flow.)

Advanced Usage

• "To move down a concentration gradient": To move passively from an area of higher concentration to an area of lower concentration. This is the principle behind diffusion.
  • Water will move down its concentration gradient through a semipermeable membrane in a process called osmosis.
• "To move against/up a concentration gradient": To move from an area of lower concentration to an area of higher concentration. This process requires energy, typically from ATP, and is called active transport.
  • Sodium-potassium pumps move sodium ions against their concentration gradient out of the cell.

Variants and Related Words

• Diffusion (n): The net movement of molecules or atoms from a region of high concentration to a region of low concentration, down a concentration gradient.
• Osmosis (n): The diffusion of water molecules across a selectively permeable membrane down a water concentration gradient.
• Electrochemical Gradient (n): A gradient resulting from the combined effects of an electrical potential and a concentration gradient.

Synonyms

• Chemical gradient: A gradient in the concentration of a chemical substance.
• Density gradient: While often used in centrifugation, it can conceptually relate to a gradient of particle concentration.

Related Phrases

• "Steep concentration gradient": A very large difference in concentration over a short distance, which typically results in a faster rate of diffusion.
  • A steep concentration gradient of perfume in the room caused it to spread quickly.
• "Establish a concentration gradient": To create a difference in concentration.
  • The cell established a proton concentration gradient across the mitochondrial membrane to store energy.

Noun

1. a gradient in concentration of a solute as a function of distance through a solution
   • the movement of a solute down its concentration gradient is called diffusion