Multiple Choice
The processes of diffusion and active transport are both used to:
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6. The Membrane
Passive vs. Active Transport
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Which of the following substances is most likely to be transported across a cell membrane by facilitated diffusion?
A
Water ($H_2O$)
B
Oxygen ($O_2$)
C
Sodium ions ($Na^+$) via the sodium-potassium pump
D
Glucose
Verified step by step guidance1
Facilitated diffusion is a type of passive transport that moves substances across the cell membrane with the help of transport proteins, without requiring energy input.
Identify the characteristics of the substances listed: Water ($H_2O$) and Oxygen ($O_2$) are small, nonpolar molecules that can diffuse directly through the lipid bilayer without the need for transport proteins. Sodium ions ($Na^+$) are transported actively via the sodium-potassium pump, which requires energy (ATP).
Glucose is a large, polar molecule that cannot pass directly through the hydrophobic lipid bilayer of the cell membrane. It requires a specific transport protein to facilitate its movement across the membrane.
Facilitated diffusion relies on carrier or channel proteins to move substances like glucose down their concentration gradient, from areas of higher concentration to areas of lower concentration.
Conclude that glucose is the substance most likely to be transported across the cell membrane by facilitated diffusion, as it matches the criteria for requiring transport proteins and moving passively along its concentration gradient.
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