Multiple Choice
In the context of passive transport, which option best defines osmosis?
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9. Transport Across Membranes
Passive Transport: Diffusion and Osmosis
Multiple Choice
Which of the following is an example of passive transport across a cell membrane?
A
Glucose entering a cell via a Na+/glucose symporter using the sodium gradient
B
Oxygen (O2) moving from a region of higher concentration to lower concentration directly through the lipid bilayer
C
Hydrogen ions being pumped across a membrane by an ATP-driven proton pump
D
A cell engulfing a bacterium by phagocytosis
Verified step by step guidance1
Understand the definition of passive transport: it is the movement of molecules across a cell membrane without the use of cellular energy (ATP), typically moving down their concentration gradient.
Analyze each option to determine if energy is required or if the molecule moves down its concentration gradient without assistance.
For glucose entering via a Na+/glucose symporter, recognize that this is a form of secondary active transport because it uses the sodium gradient (which is maintained by ATP) to move glucose against its concentration gradient.
For oxygen (O2) moving directly through the lipid bilayer from higher to lower concentration, identify this as simple diffusion, a classic example of passive transport since it requires no energy and moves down the concentration gradient.
For hydrogen ions being pumped by an ATP-driven proton pump and phagocytosis, note that both processes require energy input, so they are examples of active transport and endocytosis, respectively, not passive transport.
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