semipermeable membrane

(noun)

A type of biological membrane that will allow certain molecules or ions to pass through it by diffusion and occasionally by specialized facilitated diffusion

Related Terms

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.

  • 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.

  • 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

  • Phospholipids

    • Phospholipids are amphipathic molecules that make up the bilayer of the plasma membrane and keep the membrane fluid.
    • Phospholipids are major components of the plasma membrane, the outermost layer of animal cells.
    • The cell membrane consists of two adjacent layers of phospholipids, which form a bilayer.
    • Because of the phospholipds' chemical and physical characteristics, the lipid bilayer acts as a semipermeable membrane; only lipophilic solutes can easily pass the phospholipd bilayer.
    • As a result, there are two distinct aqueous compartments on each side of the membrane.

  • Water and Solute Potential

    • In this example with a semipermeable membrane between two aqueous systems, water will move from a region of higher to lower water potential until equilibrium is reached.

  • Membrane Fluidity

    • The mosaic nature of the membrane, its phospholipid chemistry, and the presence of cholesterol contribute to membrane fluidity.
    • There are multiple factors that lead to membrane fluidity .
    • First, the mosaic characteristic of the membrane helps the plasma membrane remain fluid.
    • It lies alongside the phospholipids in the membrane and tends to dampen the effects of temperature on the membrane.
    • Explain the function of membrane fluidity in the structure of cells

  • Components of Plasma Membranes

    • The plasma membrane protects the cell from its external environment, mediates cellular transport, and transmits cellular signals.
    • The plasma membrane (also known as the cell membrane or cytoplasmic membrane) is a biological membrane that separates the interior of a cell from its outside environment.
    • The primary function of the plasma membrane is to protect the cell from its surroundings.
    • The membrane also maintains the cell potential.
    • The cell employs a number of transport mechanisms that involve biological membranes:

  • Fluid Mosaic Model

    • Nicolson in 1972 to explain the structure of the plasma membrane.
    • Plasma membranes range from 5 to 10 nm in thickness.
    • Proteins make up the second major component of plasma membranes.
    • The fluid mosaic model of the plasma membrane describes the plasma membrane as a fluid combination of phospholipids, cholesterol, and proteins.
    • Integral membrane proteins may have one or more alpha-helices that span the membrane (examples 1 and 2), or they may have beta-sheets that span the membrane (example 3).

  • Molecules in Biological Membranes

  • Transport of Electrolytes across Cell Membranes

    • Water passes through semi-permeable membranes by passive diffusion, moving along a concentration gradient and equalizing the concentration on either side of the membrane.
    • Electrolyte ions may not be able to passively diffuse across a membrane, but may instead require special mechanisms to cross the semi-permeable membrane.
    • The mechanisms that transport ions across membranes are facilitated diffusion and active transport.
    • Paul Andersen describes how cells move materials across the cell membrane.
    • Explain the relationship between osmotic pressure and the transport of electrolytes across cell membranes