semipermeable membrane

Examples of semipermeable membrane in the following topics:

• 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.
  • Semipermeable membranes, also termed selectively permeable membranes or partially permeable membranes, allow certain molecules or ions to pass through by diffusion.
  • While diffusion transports materials across membranes and within cells, osmosis transports only water across a membrane.
  • The semipermeable membrane limits the diffusion of solutes in the water.
  • Imagine a beaker with a semipermeable membrane separating the two sides or halves.

• Osmotic Pressure

  • Osmotic pressure is the pressure which must be applied to a solution to prevent the inward flow of water across a semipermeable membrane.
  • Osmotic pressure is the pressure which needs to be applied to a solution to prevent the inward flow of water across a semipermeable membrane.
  • It is also defined as the minimum pressure needed to nullify osmosis.The phenomenon of osmotic pressure arises from the tendency of a pure solvent to move through a semi-permeable membrane and into a solution containing a solute to which the membrane is impermeable.
  • As a result, when a cell is placed in a hypotonic solution, water rushes into the membrane, increasing its volume.
  • Eventually, the cell's membrane is enlarged such that it pushes against the cell's rigid wall.

• Osmotic Pressure

  • Osmosis is defined as the net flow or movement of solvent molecules through a semipermeable membrane through which solute molecules cannot pass.
  • If a solution consisting of both solute and solvent molecules is placed on one side of a membrane and pure solvent is placed on the other side, there is a net flow of solvent into the solution side of the membrane.
  • Osmotic pressure is the pressure that needs to be applied to a solution to prevent the inward flow of water across a semipermeable membrane.
  • One way to stop osmosis is to increase the hydrostatic pressure on the solution side of the membrane; this ultimately squeezes the solvent molecules closer together, increasing their "escaping tendency."
  • The pure water is trying to dilute the solution by travelling through the semipermeable membrane.

• Selective Permeability

  • Plasma membranes are asymmetric: the interior of the membrane is not identical to the exterior of the membrane.
  • On the interior of the membrane, some proteins serve to anchor the membrane to fibers of the cytoskeleton.
  • Polar substances present problems for the membrane.
  • This interactive shows that smaller molecules have an easier time making it across a semipermeable membrane.
  • The exterior surface of the plasma membrane is not identical to the interior surface of the same membrane.

• Biological and Medical Applications

  • Another important form of fluid movement is osmosis—the transport of water through a semipermeable membrane (shown in ) from a region of high concentration to a region of low concentration.
  • Similarly, dialysis is the transport of any other molecule through a semipermeable membrane due to its concentration difference.
  • A semipermeable membrane with small pores that allow only small molecules to pass through.

• Molecular Transport Phenomena

  • Diffusion through membranes is an important method of transport.
  • Membranes are generally selectively permeable, or semipermeable.
  • In other types of membranes, the molecules may actually dissolve in the membrane or react with molecules in the membrane while moving across.
  • Similarly, dialysis is the transport of any other molecule through a semipermeable membrane due to its concentration difference.
  • (a) Two sugar-water solutions of different concentrations, separated by a semipermeable membrane that passes water but not sugar.

• Dialysis

  • Dialysis works on the principles of the diffusion of solutes and ultrafiltration of fluid across a semi-permeable membrane.
  • Blood flows by one side of a semi-permeable membrane, and a dialysate, or special dialysis fluid, flows by the opposite side.
  • A semipermeable membrane is a thin layer of material that contains holes of various sizes, or pores.
  • Smaller solutes and fluid pass through the membrane, but the membrane blocks the passage of larger substances (for example, red blood cells, large proteins).
  • Hemodialysis removes wastes and water by circulating blood outside the body through an external filter, called a dialyzer, that contains a semipermeable membrane.

• Nerve Conduction and Electrocardiograms

  • The cell membrane is semipermeable, meaning that some ions may cross it while others cannot.
  • How does it get transmitted along the cell membrane as a nerve impulse?
  • The adjacent membrane depolarizes, affecting the membrane farther down, and so on.
  • The semipermeable membrane of a cell has different concentrations of ions inside and out.
  • The membrane is normally impermeable to Na+.

• The Plasma Membrane and the Cytoplasm

  • Despite differences in structure and function, all living cells in multicellular organisms have a surrounding plasma membrane (also known as the cell membrane).
  • Cholesterol, also present, contributes to the fluidity of the membrane.
  • This structure causes the membrane to be selectively permeable.
  • Osmosis is the diffusion of water through a semipermeable membrane down its concentration gradient.
  • Explain the structure and purpose of the plasma membrane of a cell

• Electric Potential in Human

  • In humans, they are seen in cell membranes and nerve impulses in particular.
  • Cell membranes are only semipermeable; water can freely travel in and out, but ions can be selectively admitted passage across them.
  • Potentials can change as ions move across the cell membrane.
  • This can occur passively, as ions diffuse through ion channels in the membrane.
  • Active transport of ions across a cell membrane is also a possibility.