Multiple Choice
In passive transport, how does increasing temperature affect the rate of diffusion of small molecules across a solution or membrane (assuming no phase change and constant concentration gradient)?
9. Transport Across Membranes
Passive Transport: Diffusion and Osmosis
Multiple Choice
Which scenario is the best model of diffusion (passive movement of particles down their concentration gradient)?
A
Perfume molecules spreading from a high concentration near the spray to a lower concentration throughout a room
B
Glucose entering a cell via a membrane pump that uses ATP to move it against its concentration gradient
C
Water moving across a selectively permeable membrane toward the side with higher solute concentration (osmosis)
D
Ions moving through a membrane channel from lower concentration to higher concentration because of energy input
Verified step by step guidance1
Step 1: Understand the definition of diffusion. Diffusion is the passive movement of particles from an area of higher concentration to an area of lower concentration without the use of energy (ATP).
Step 2: Analyze each scenario to determine if it involves passive movement down a concentration gradient (diffusion) or active transport requiring energy.
Step 3: Identify that the scenario where perfume molecules spread from a high concentration near the spray to a lower concentration throughout a room exemplifies diffusion, as it involves passive movement down the concentration gradient without energy input.
Step 4: Recognize that glucose entering a cell via a membrane pump using ATP is active transport, not diffusion, because it moves molecules against their concentration gradient using energy.
Step 5: Note that water moving across a membrane toward higher solute concentration is osmosis, a special type of diffusion specific to water, and ions moving from lower to higher concentration with energy input is active transport, not diffusion.
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