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Transport across cell membranes


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Plasma membrane
A microscopic membrane of lipids and proteins that forms the external boundary of the cytoplasm of a cell or encloses a vacuole, and that regulates the passage of molecules in and out of the cytoplasm.
Carrier protein
A protein on surface of a cell that helps to transport molecules and ions across plasma membranes
Facilitated diffusion
Diffusion involving the presence of protein carrier molecules to allow the passive movement of substances across a membrane
Diffusion
The movement of molecules or ions from a region where they are in high concentration to one where their concentration is low
Osmosis
The passage of water from a region where it has a higher water potential to a region where it has a lower water potential through a partially permeable membrane
Hypotonic
Having a lower osmotic pressure than a particular fluid, typically a body fluid or intracellular fluid
Isotonic
Having an equal osmotic pressure than a particular fluid, typically a body fluid or intracellular fluid
Hypertonic
Having a higher osmotic pressure than a particular fluid, typically a body fluid or intracellular fluid
Phospholipid
A lipid in which one of the fatty acid molecules is replaced with a phosphate group
Water potential
The pressure created by water molecules. It measures the extent to which a solution gives out water. The greater the number of water molecules present, the higher (less negative) the water potential is. Pure water has a water potential of zero.
Solutes
A substance that has been dissolved in a liquid
Solvents
The liquid that a substance is dissolved in
Hydrophobic
Mixes readily with fat but not water
Hydrophilic
Attracted to water
Polar
Molecules that have one hydrophobic and one hydrophilic region
Extrinsic proteins
Proteins that occur on the surface of the plasma membrane or embed in it but that never completely span the phospholipid bilayer
Intrinsic proteins
Proteins that completely span the plasma membrane
Dynamic Equilibrium
When the number of particles of a solute on either side of a partially permeable membrane are the equal but individual particles are constantly crossing the membrane
Concentration gradient
The gradual difference in concentration of a dissolved substance in a solution between a region of high concentration and one of lower concentration
Partially-permeable membrane
A membrane that is permeable to the small molecules of water and certain solutes but does not allow the passage of large molecules
Kinetic energy
The energy possessed by a body because of its motion
Solution
A solvent with solute dissolved in it
Dehydration
The loss of water and salts that are essential for normal body function
Turgid
The protoplast of a plant cell is kept pushed against the cell wall
Ion channels
A protein that acts as a pore in a cell membrane and permits the selective passage of ions
Incipient plasmolysis
The protoplast of a plant no longer presses against the cell wall
Active transport
The movement of molecules or ions into or out of a cell from a region of lower concentration to a region of higher concentration using energy and carrier molecules
Plasmolysed
The contents of a plant cell have shrunk and the protoplast pulls away from the cell wall
Cotransport
The simultaneous transport of two substrates across a cell membrane by one carrier protein
Protoplast
The outer cell surface membrane, nucleus, cytoplasm and inner vacuole membrane of a plant cell
Endocytosis
The process of cellular ingestion by which the plasma membrane folds inward to bring substances into the cell
Exocytosis
The process by which the contents of a cell vacuole are released to the exterior through fusion of the vacuole membrane with the cell membrane