Multiple Choice
Osmosis is best defined as which of the following processes?
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9. Transport Across Membranes
Passive Transport: Diffusion and Osmosis
Multiple Choice
Which of the following is a passive transport process that moves molecules down their concentration gradient without requiring cellular energy (ATP)?
A
Endocytosis of extracellular fluid (pinocytosis) into a vesicle
B
Simple diffusion of oxygen across the plasma membrane
C
Exocytosis of neurotransmitters from a synaptic vesicle
D
Active transport of sodium ions by the Na+/K+ ATPase pump
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), typically moving down their concentration gradient.
Step 2: Review each option to determine if it requires energy or moves molecules against their concentration gradient. For example, endocytosis and exocytosis involve vesicle formation and require energy, so they are active processes.
Step 3: Recognize that simple diffusion is a passive process where molecules like oxygen move directly across the plasma membrane from an area of higher concentration to an area of lower concentration without energy input.
Step 4: Identify that active transport, such as the Na+/K+ ATPase pump, uses ATP to move ions against their concentration gradient, so it is not passive transport.
Step 5: Conclude that the process described as simple diffusion of oxygen across the plasma membrane fits the criteria of passive transport moving molecules down their concentration gradient without requiring ATP.
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