TRANSPORT OF MATERIALS ACROSS THE CELL MEMBRANE AND CELL WALL Flashcards
maintenance of a steady living state or equilibrium in the midst of an ever-changing environment
cell membranes
maintained by the regulation of the transport of substances into and out of the cell
equilibrium
Cellular activities such as growth, absorption, and respiration all involve the transport of dissolved substances through the ____________
cytoplasmic membranes
kind of passive transport. It is the tendency for dissolved molecules to move from a region of higher concentration to that of lower concentration
This process is possible only for solutes that are readily permeable such as nonpolar and small polar molecules.
Simple diffusion
influences many activities of the cell, including cell growth, structural rigidity, and photosynthesis
moves across cell membranes by simple diffusion
also has potential energy to flow to where it is less concentrated
Water
diffusion of water through a selectively permeable membrane
Water flows passively from one place to another because of differences in potential energy
osmosis
potential energy of water
water potential or psi (Ψw)
The tendency for water to move into and out of the cell is determined by the difference between ____ and the ____
cell contents, external medium
represents the suction force of the cell or the difference between the activity of pure water and water in any other system
water potential or psi (Ψw)
water potential of pure water is
zero
water potential is expressed in units of pressure
megaspascals (Mpa)
relationship between water potential and its components may be expressed mathematically as:
Ψw = Ψs + Ψp
is the water potential of a cell. Plant cells usually have a negative water potential, unless they are in equilibrium with pure water. Such cells are fully turgid and have a Ψ equal to zero.
Ψw
is solute or osmotic potential, the contribution made by dissolved solutes. It is always negative in sign. The addition of solutes lowers the water potential of the solution proportionally.
Ψs
is pressure or turgor potential and is related to the counter-pressure exerted by the cell wall as the expanding vacuole presses the plasma membrane against the cell wall if a plant cell is placed in a hypotonic medium.
Ψp
