ch. 5 passive transport across membranes

Question 1

passive transport

Answer 1

when substances can move in and out of the cell without the cell having to expand energy.

Question 2

some ions and molecules can pass through the membrane easily because of a _________ _________.

Answer 2

concentration gradient.

Question 3

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

Answer 3

diffusion

Question 4

major barrier to crossing a biological membrane

Answer 4

hydrophobic interior that repels polar molecules but not non polar molecules

Question 5

the plasma membrane has

Answer 5

limited permeability to small polar molecules and very limited permeability to larger polar molecules and ions.

Question 6

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

Answer 6

facilitated diffusion

Question 7

channel proteins have

Answer 7

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.

Question 8

ions interact well with _______ molecules, but are repelled by ________ molecules such as the interior of the plasma membrane.

Answer 8

polar, nonpolar

Question 9

ion channels possess

Answer 9

a hydrated interior that spans the membrane.

Question 10

three conditions determine the direction of net movement of the ions:

Answer 10

1. their relative concentrations on either side of the membrane
2. the voltage difference across the membrane
3. the state of the gate (open or closed)

Question 11

______ ________ can help transport both ions and other solutes, such as some sugars and amino acids, across the membrane.

Answer 11

carrier proteins

Question 12

the mixture of ions and molecules and water is called an ________ solution

Answer 12

aqueous

Question 13

water is termed the _______, and the substances dissolved in water are ______.

Answer 13

solvent, solutes

Question 14

water molecules interact with dissolved solutes by forming

Answer 14

hydration shells around the charged solute molecules

Question 15

the side with higher solute concentration has tied up more water molecules in hydration shells and thus has

Answer 15

fewer free water molecules.

Question 16

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

Answer 16

osmosis.

Question 16

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

Answer 16

osmosis.

Question 17

the concentration of all solutes in a solution determines the _______ _______ of the solution.

Answer 17

osmotic concentration

Question 18

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 _______.

Answer 18

hypertonic, hypotonic, isotonic

Question 19

a cell in any environment can be thought of as a plasma membrane separating two solutions:

Answer 19

the cytoplasm and the extracellular fluid

Question 20

water flow in living cells is facilitated by ________, which are specialized channels for water,

Answer 20

aquaporins

Question 21

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.

Answer 21

osmotic pressure

Question 22

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:

Answer 22

1. extrusion
2. isotonic regulation
3. turgor

Question 23

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:

Answer 23

1. extrusion
2. isotonic regulation
3. turgor