requires the aid of transport proteins
Any molecule smaller than the holes in the membrane can pass through is the membrane is permeable. If the membrane is semi-permeable, then only molecules that the membrane selects can pass through. Electronegativity and existence of lipid layers are common selective traits for semi-permeable membranes.
There are three types of transport for molecules across the cell membrane. 1 - Diffusion - Molecules move from an area of high concentration to an area of low concentration 2 - Osmosis - same idea as diffusion, but refers to the movement of WATER across a selectively permeable membrane. How can you change water concentration? Add a solute. If you have 2 250 ml beakers, connected and divided by a selectively permeable membrane, and one beaker contains a salt solution, the salt solution is "hypotonic" (hypo- less, tonic - water) to the water filled beaker. One will see a migration of water into the salt solution beaker. BOTH diffusion and osmosis rely on concentration gradients to perform their jobs. They always want "equilibrium" between both sides of the membrane. 3 - Active transport - Proteins embedded in the cell membrane move large molecules through the cell membrane or AGAINST the concentration gradient. The size one is obvious; If it's really big, it won't permeate the membrane. As for the concentration gradient, this means that it moves a molecule INTO the area with and already HIGHER concentration. If this happens with say... H+ molecules, it creates a potential difference - ie - Voltage across the membrane. Cellular respiration counts on this process to create ATP/Energy for the cell.
Most of the bilayer is hydrophobic; therefore water or water-soluble molecules do not pass through easily. Usually only fat soluble are allowed through.A cell controls what moves through the membrane by means of membrane proteins embedded in the phospholipid bilayer Some membrane proteins have carbohydrates attached to them, forming glycoproteins that act as identification markers.
Most of the bilayer is hydrophobic; therefore water or water-soluble molecules do not pass through easily. Usually only fat soluble are allowed through.A cell controls what moves through the membrane by means of membrane proteins embedded in the phospholipid bilayer Some membrane proteins have carbohydrates attached to them, forming glycoproteins that act as identification markers.
this means that it allows some materials, but not all, to cross it, or permeate it.
No; the sucrose molecule (as a disaccharide) is too large to pass through by passive diffusion. Glucose, on the other hand, (a monosaccharide) is able to permeate the dialysis tubing. In the body, glucose/sucrose is transmitted across membranes though the use of active/facilitated diffusion.
Because small non polar molecules are the ones able to cross due to the fact that the membrane consists of a phospholipid bilayer where the middle is composed on non polar tails
Any molecule smaller than the holes in the membrane can pass through is the membrane is permeable. If the membrane is semi-permeable, then only molecules that the membrane selects can pass through. Electronegativity and existence of lipid layers are common selective traits for semi-permeable membranes.
the ability to allow materials to cross a membrane
Because the permeation through a membrane depends on the diffusivity (size of the permeate molecules) and the solubility (briefly the interaction equilibrium) of the permeate in the membrane. Considering permeate mixtures, membranes can be size-selective and sorption-selective depending on which relative term (ratio of diffusivities or ratio of solubilities) dominates. Most known membrane separation processes involve size-selectivity, i.e., the "smaller" the permeate molecule, the faster it gets through the membrane. More sophisticated membrane separation processes are sorption selective, where it is possible that the "bigger" molecules exhibit a higher permeation flux than the "smaller" ones.
There is no single-word opposite of "permeate," which means to spread throughout an area or to pass through a membrane.
The selectively permeable phospholipid bilayer (a.k.a plasma membrane) is 'selectively permeable' because it selects which molecules it allows to permeate (pass through).
There are three types of transport for molecules across the cell membrane. 1 - Diffusion - Molecules move from an area of high concentration to an area of low concentration 2 - Osmosis - same idea as diffusion, but refers to the movement of WATER across a selectively permeable membrane. How can you change water concentration? Add a solute. If you have 2 250 ml beakers, connected and divided by a selectively permeable membrane, and one beaker contains a salt solution, the salt solution is "hypotonic" (hypo- less, tonic - water) to the water filled beaker. One will see a migration of water into the salt solution beaker. BOTH diffusion and osmosis rely on concentration gradients to perform their jobs. They always want "equilibrium" between both sides of the membrane. 3 - Active transport - Proteins embedded in the cell membrane move large molecules through the cell membrane or AGAINST the concentration gradient. The size one is obvious; If it's really big, it won't permeate the membrane. As for the concentration gradient, this means that it moves a molecule INTO the area with and already HIGHER concentration. If this happens with say... H+ molecules, it creates a potential difference - ie - Voltage across the membrane. Cellular respiration counts on this process to create ATP/Energy for the cell.
It can permeate some stuff but not everything
Permeability depends on membrane solubility and the presence of specific integral transport proteins. Other factors such as pressure, concentration, and temperature of the molecules or solutes on either side, as well as the size of the molecules can also affect permeability.
because the external surface of the cell is is hydrophobic (water hating) many fat soluble products such as carbon dioxide are able to pass through.
Most of the bilayer is hydrophobic; therefore water or water-soluble molecules do not pass through easily. Usually only fat soluble are allowed through.A cell controls what moves through the membrane by means of membrane proteins embedded in the phospholipid bilayer Some membrane proteins have carbohydrates attached to them, forming glycoproteins that act as identification markers.