ch. 5 passive transport across membranes Flashcards
passive transport
when substances can move in and out of the cell without the cell having to expand energy.
some ions and molecules can pass through the membrane easily because of a _________ _________.
concentration gradient.
molecules and ions dissolved in water are in constant random motion. This causes a net movement of these substances from regions of high concentration to regions of lower concentration, a process called
diffusion
major barrier to crossing a biological membrane
hydrophobic interior that repels polar molecules but not non polar molecules
the plasma membrane has
limited permeability to small polar molecules and very limited permeability to larger polar molecules and ions.
many molecules required by cells can’t cross the plasma membrane. these molecules can still enter by diffusion through specific channel proteins or carrier proteins embedded in the plasma membrane. This process of diffusion mediated by a membrane protein is called
facilitated diffusion
channel proteins have
a hydrophilic interior that provides an aqueous channel through which polar molecules can pass when the channel is open.
-so, the cell membrane is said to be selectively permeable.
ions interact well with _______ molecules, but are repelled by ________ molecules such as the interior of the plasma membrane.
polar, nonpolar
ion channels possess
a hydrated interior that spans the membrane.
three conditions determine the direction of net movement of the ions:
- their relative concentrations on either side of the membrane
- the voltage difference across the membrane
- the state of the gate (open or closed)
______ ________ can help transport both ions and other solutes, such as some sugars and amino acids, across the membrane.
carrier proteins
the mixture of ions and molecules and water is called an ________ solution
aqueous
water is termed the _______, and the substances dissolved in water are ______.
solvent, solutes
water molecules interact with dissolved solutes by forming
hydration shells around the charged solute molecules
the side with higher solute concentration has tied up more water molecules in hydration shells and thus has
fewer free water molecules.
free water molecules move down their concentration gradient, toward the higher solute concentration. this net diffusion of water across a membrane toward a higher solute concentration is called
osmosis.
free water molecules move down their concentration gradient, toward the higher solute concentration. this net diffusion of water across a membrane toward a higher solute concentration is called
osmosis.
the concentration of all solutes in a solution determines the _______ _______ of the solution.
osmotic concentration
the solution with the higher osmotic concentration is ________, and the solution with the lower concentration is ________. when two solutions have the same osmotic concentration, the solutions are _______.
hypertonic, hypotonic, isotonic
a cell in any environment can be thought of as a plasma membrane separating two solutions:
the cytoplasm and the extracellular fluid
water flow in living cells is facilitated by ________, which are specialized channels for water,
aquaporins
the amount of water that enters the cell is a hypotonic solution depending on the difference in solute concentration between the cell and the extracellular fluid. This is measured as _______ _______, defines as the force needed to stop osmotic flow.
osmotic pressure
organisms have developed many strategies for solving the dilemma posed by being hypertonic to their environment and therefore having a steady influx of water by osmosis:
- extrusion
- isotonic regulation
- turgor
organisms have developed many strategies for solving the dilemma posed by being hypertonic to their environment and therefore having a steady influx of water by osmosis:
- extrusion
- isotonic regulation
- turgor
