Multiple Choice
In passive transport, water moves via osmosis from a region of ________ to a region of ________ across a selectively permeable membrane.
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9. Transport Across Membranes
Passive Transport: Diffusion and Osmosis
Multiple Choice
Which of the following is NOT a form of passive transport across a cell membrane?
A
Simple diffusion
B
Facilitated diffusion through a channel protein
C
Primary active transport via an ATP-driven pump
D
Osmosis
Verified step by step guidance1
Step 1: Understand the definition of passive transport. Passive transport is the movement of molecules across a cell membrane without the use of cellular energy (ATP). It relies on the concentration gradient, moving substances from an area of higher concentration to an area of lower concentration.
Step 2: Identify examples of passive transport. Simple diffusion is the direct movement of small or nonpolar molecules through the lipid bilayer. Facilitated diffusion involves channel or carrier proteins helping molecules move down their concentration gradient without energy input. Osmosis is the passive diffusion of water across a selectively permeable membrane.
Step 3: Recognize what primary active transport is. Primary active transport uses energy from ATP hydrolysis to move molecules against their concentration gradient, which requires cellular energy and is not passive.
Step 4: Compare the options given. Simple diffusion, facilitated diffusion through a channel protein, and osmosis all fit the criteria of passive transport because they do not require energy. Primary active transport via an ATP-driven pump requires energy and moves substances against their gradient, so it is not passive.
Step 5: Conclude that the correct answer is the option that involves energy use and movement against the concentration gradient, which is primary active transport via an ATP-driven pump.
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