concentration gradient

Examples of concentration gradient in the following topics:

• Secondary Active Transport

  • In secondary active transport, a molecule is moved down its electrochemical gradient as another is moved up its concentration gradient.
  • Instead, another molecule is moved up its concentration gradient, which generates an electrochemical gradient.
  • The molecule of interest is then transported down the electrochemical gradient.
  • As sodium ion concentrations build outside the plasma membrane because of the action of the primary active transport process, an electrochemical gradient is created.
  • An electrochemical gradient, created by primary active transport, can move other substances against their concentration gradients, a process called co-transport or secondary active transport.

• Diffusion

  • On the contrary, concentration gradients are a form of potential energy, dissipated as the gradient is eliminated.
  • Each separate substance in a medium, such as the extracellular fluid, has its own concentration gradient independent of the concentration gradients of other materials.
  • This lack of a concentration gradient in which there is no net movement of a substance is known as dynamic equilibrium.
  • Extent of the concentration gradient: The greater the difference in concentration, the more rapid the diffusion.
  • Diffusion through a permeable membrane moves a substance from an area of high concentration (extracellular fluid, in this case) down its concentration gradient (into the cytoplasm).

• Osmosis

  • Osmosis is the movement of water through a semipermeable membrane according to the concentration gradient of water across the membrane, which is inversely proportional to the concentration of solutes.
  • Water has a concentration gradient in this system.
  • Thus, water will diffuse down its concentration gradient, crossing the membrane to the side where it is less concentrated.
  • This diffusion of water through the membrane—osmosis—will continue until the concentration gradient of water goes to zero or until the hydrostatic pressure of the water balances the osmotic pressure.
  • Describe the process of osmosis and explain how concentration gradient affects osmosis

• The Role of Passive Transport

  • In passive transport, substances move from an area of higher concentration to an area of lower concentration .
  • A physical space in which there is a range of concentrations of a single substance is said to have a concentration gradient.
  • In solutions containing more than one substance, each type of molecule diffuses according to its own concentration gradient, independent of the diffusion of other substances.
  • Many factors can affect the rate of diffusion, including, but not limited to, concentration gradient, size of the particles that are diffusing, and temperature of the system.
  • Diffusion through a permeable membrane moves a substance from an area of high concentration (extracellular fluid, in this case) down its concentration gradient (into the cytoplasm).

• Electrochemical Gradient

  • Simple concentration gradients are differential concentrations of a substance across a space or a membrane, but in living systems, gradients are more complex.
  • The electrical gradient of K+, a positive ion, also tends to drive it into the cell, but the concentration gradient of K+ tends to drive K+ out of the cell.
  • The combined gradient of concentration and electrical charge that affects an ion is called its electrochemical gradient .
  • To move substances against a concentration or electrochemical gradient, the cell must use energy.
  • Electrochemical gradients arise from the combined effects of concentration gradients and electrical gradients.

• Transport of Electrolytes across Cell Membranes

  • Osmotic pressure is influenced by the concentration of solutes in a solution.
  • Water passes through semi-permeable membranes by passive diffusion, moving along a concentration gradient and equalizing the concentration on either side of the membrane.
  • Active transport requires energy in the form of ATP conversion, carrier proteins, or pumps in order to move ions against the concentration gradient.
  • Passive transport, such as diffusion, requires no energy as particles move along their gradient.
  • Active transport requires additional energy as particles move against their gradient.

• The Plasma Membrane and the Cytoplasm

  • During this type of transport, materials move by simple diffusion or by facilitated diffusion through the membrane, down their concentration gradient.
  • Osmosis is the diffusion of water through a semi-permeable membrane down its concentration gradient.
  • The energy is expended to assist material movement across the membrane in a direction against their concentration gradient.
  • Osmosis is the diffusion of water through a semipermeable membrane down its concentration gradient.
  • If a membrane is permeable to water, though not to a solute, water will equalize its own concentration by diffusing to the side of lower water concentration (and thus the side of higher solute concentration).

• Chemiosmosis and Oxidative Phosphorylation

  • Chemiosmosis is the movement of ions across a selectively permeable membrane, down their electrochemical gradient.
  • The uneven distribution of H+ ions across the membrane establishes both concentration and electrical gradients (thus, an electrochemical gradient) owing to the hydrogen ions' positive charge and their aggregation on one side of the membrane.
  • This protein acts as a tiny generator turned by the force of the hydrogen ions diffusing through it, down their electrochemical gradient.
  • In oxidative phosphorylation, the hydrogen ion gradient formed by the electron transport chain is used by ATP synthase to form ATP.
  • ATP synthase is a complex, molecular machine that uses a proton (H+) gradient to form ATP from ADP and inorganic phosphate (Pi).

• Primary Active Transport

  • The sodium-potassium pump maintains the electrochemical gradient of living cells by moving sodium in and potassium out of the cell.
  • One of the most important pumps in animals cells is the sodium-potassium pump (Na+-K+ ATPase), which maintains the electrochemical gradient (and the correct concentrations of Na+ and K+) in living cells.
  • Primary active transport moves ions across a membrane, creating an electrochemical gradient (electrogenic transport).
  • Describe how a cell moves sodium and potassium out of and into the cell against its electrochemical gradient

• Gas Exchange across the Alveoli

  • This results in a lower concentration of oxygen in the lungs than is found in the air outside the body.
  • Since this pressure gradient exists, oxygen can diffuse down its pressure gradient, moving out of the alveoli and entering the blood of the capillaries where O2 binds to hemoglobin.
  • Due to this gradient, CO2 diffuses down its pressure gradient, moving out of the capillaries and entering the alveoli.
  • This pressure gradient drives the diffusion of oxygen out of the capillaries and into the tissue cells.
  • The pressure gradient drives CO2 out of tissue cells and into the capillaries.