1.3 Cell membranes and transport Flashcards
Fluid mosaic model
Model of the structure of biological membranes, in which proteins are studded throughout a phospholipid bilayer, as in a mosaic. The movement of molecules within a layer of the bilayer is its fluidity
Diffusion
The passive movement of molecules or ions down a concentration gradient, from a region of high concentration to a region of low concentration
Passive
Not requiring energy provided by the cell
Facilitated diffusion
The passive transfer of molecules or ions down a concentration gradient, across a membrane, by channel or carrier proteins in the membrane
Active transport
The movement of molecules or ions across a membrane against a concentration gradient, using energy from the hydrolysis of ATP made by the cells in respiration.
Co-transport
A transport mechanism in which facilitated diffusion brings molecules or ions (such as glucose and sodium ions) across the cell membrane together into a cell
Osmosis
The net passive diffusion of water molecules across a selectively permeable membrane from a region of high water potential to a region of lower water potential.
Water potential
The tendency for water to move into a system; water moved from a high water potential (less negative) to one with a lower water potential (more negative)
How is water potential is decreased?
With the addition of a solute
Pure water’s water potential
0
Solute potential
The reduction in water potential due to the presence of solute molecules.
Water potential +ve or -ve
-ve
Solute potential +ve or -ve
-ve
Turgid
A plant cell that holds as much water as possible. Further entry of water is prevented as the cell wall cannot expand further.
Pressure potential
The hydrostatic pressure exerted by the cell contents on the cell wall. It is equal and opposite to the pressure exerted by the cell wall on the cell contents
Plasmolysis
The retraction of the cytoplasm and cell membrane from the cell wall as the cell loses water by osmosis.
Incipient plasmolysis
Cell membrane and cytoplasm are partially detached from cell wall due to not enough water to make the cell turgid. Pressure potential = 0, water potential of cell = solute potential of external solution
Endocytosis
The active process of the cell membrane engulfing material, bringing it into the cell in a vesicle
Exocytosis
The active process of a vesicle fusing with the cell membrane, releasing the molecules it contains.
Phagocytosis
The active process of the cell membrane engulfing large particles, bringing it into the cell in a vesicle.
Pinocytosis
The active process of the cell membrane engulfing droplets of a fluid, bringing it into the cell in a vesicle.
