Multiple Choice
Which characteristic of the plasma membrane contributes to its selective permeability?
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6. The Membrane
Biological Membranes
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Why are O2 and CO2 able to pass through the plasma membrane easily?
A
They are large and charged molecules.
B
They require energy in the form of ATP to pass through.
C
They are small and nonpolar molecules.
D
They are actively transported by membrane proteins.
Verified step by step guidance1
Understand the structure of the plasma membrane: The plasma membrane is primarily composed of a phospholipid bilayer, which has hydrophobic (water-repelling) tails and hydrophilic (water-attracting) heads.
Recognize the properties of O2 and CO2: Both oxygen (O2) and carbon dioxide (CO2) are small, nonpolar molecules. Nonpolar molecules do not have a charge, which allows them to interact easily with the hydrophobic tails of the phospholipids.
Identify the mechanism of passive diffusion: Small, nonpolar molecules like O2 and CO2 can pass through the plasma membrane via passive diffusion. This process does not require energy and occurs due to the concentration gradient, where molecules move from an area of higher concentration to an area of lower concentration.
Contrast with other transport mechanisms: Large or charged molecules typically require assistance to cross the membrane, often through facilitated diffusion or active transport, which involves membrane proteins and sometimes energy in the form of ATP.
Summarize why O2 and CO2 pass easily: Due to their small size and nonpolar nature, O2 and CO2 can easily diffuse across the plasma membrane without the need for energy or transport proteins.
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