Multiple Choice
Which of the following substances is most likely to cross a cell membrane by simple diffusion rather than facilitated diffusion?
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6. The Membrane
Passive vs. Active Transport
Multiple Choice
Which of the following molecules is most likely to cross a cell membrane by simple diffusion rather than facilitated diffusion?
A
Amino acid
B
O\(_2\) (oxygen gas)
C
Glucose
D
Na\(^+\) (sodium ion)
Verified step by step guidance1
Understand the difference between simple diffusion and facilitated diffusion: Simple diffusion allows small, nonpolar molecules to pass directly through the lipid bilayer of the cell membrane without the need for transport proteins. Facilitated diffusion, on the other hand, requires the assistance of specific transport proteins to move larger, polar, or charged molecules across the membrane.
Analyze the properties of each molecule: Oxygen gas (O\(_2\)) is small and nonpolar, making it highly likely to cross the membrane via simple diffusion. Amino acids, glucose, and sodium ions (Na\(^+\)) are either polar, charged, or too large to pass through the lipid bilayer without assistance.
Consider the role of polarity and charge: Polar molecules like glucose and charged ions like Na\(^+\) cannot easily pass through the hydrophobic core of the lipid bilayer. They require transport proteins for facilitated diffusion.
Evaluate the size and hydrophobicity of O\(_2\): Oxygen gas is both small and nonpolar, which allows it to dissolve in the hydrophobic lipid bilayer and diffuse across the membrane without the need for a transport protein.
Conclude that O\(_2\) is the molecule most likely to cross the cell membrane by simple diffusion, as it meets the criteria of being small, nonpolar, and uncharged, unlike the other molecules listed.
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