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Which of the following statements is FALSE regarding the diffusion of substances through membranes?

a. Water can diffuse through the lipid bilayer because it is small.
b. Substances with a larger partition coefficient are better able to diffuse through the lipid bilayer.
c. Diffusion across a membrane requires a concentration gradient.
d. A membrane is permeable to a substance that can cross through the lipid bilayer or through an aqueous pore that spans the membrane.
e. Glucose passively diffuses into cells where it is used as a nutrient.

1 Answer

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Final answer:

The false statement is that glucose passively diffuses into cells. In reality, glucose requires facilitated diffusion through a specialized protein because it is a large and polar molecule.

Step-by-step explanation:

The statement, "Glucose passively diffuses into cells where it is used as a nutrient," is FALSE regarding the diffusion of substances through membranes. Glucose is a large and polar molecule that cannot cross the cell membrane via simple diffusion. Instead, glucose requires a process known as facilitated diffusion, where a specialized protein, the glucose transporter, helps to move glucose across the membrane, down its concentration gradient.

Passive transport of molecules like oxygen and carbon dioxide can happen easily through the lipid bilayer because they are small and nonpolar. Large polar or ionic molecules, however, are hydrophilic and cannot easily pass through the hydrophobic interior of the phospholipid bilayer without assistance from transport proteins.

Regarding the partition coefficient, substances with a larger partition coefficient are indeed better able to diffuse through the lipid bilayer as they tend to be more hydrophobic and can interact more easily with the lipid tails of the bilayer. Thus, substances with higher partition coefficients tend to dissolve better in fats than in water.

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