Multiple Choice
In passive transport, the principal force driving net movement of molecules during diffusion across a membrane is the:
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9. Transport Across Membranes
Passive Transport: Diffusion and Osmosis
Multiple Choice
Which statement best describes how the magnitude of a concentration gradient affects the net rate of diffusion across a membrane in passive transport?
A
A steeper concentration gradient produces a faster net diffusion rate.
B
Net diffusion occurs only when solute concentrations are equal on both sides of the membrane.
C
The net diffusion rate is independent of the concentration gradient as long as the temperature is constant.
D
A steeper concentration gradient produces a slower net diffusion rate.
Verified step by step guidance1
Understand that diffusion is the movement of molecules from an area of higher concentration to an area of lower concentration across a membrane, driven by the concentration gradient.
Recognize that the concentration gradient is the difference in solute concentration between the two sides of the membrane, and it acts as the driving force for diffusion.
Recall Fick's first law of diffusion, which states that the net rate of diffusion (\(J\)) is proportional to the concentration gradient (\(\Delta C\)), expressed as:
\(J = -D \times \frac{\Delta C}{\Delta x}\)
where \(D\) is the diffusion coefficient and \(\Delta x\) is the thickness of the membrane.
Note that a steeper concentration gradient means a larger \(\Delta C\), which increases the magnitude of \(J\), leading to a faster net diffusion rate.
Conclude that when the concentrations on both sides are equal, \(\Delta C = 0\), so there is no net diffusion, and the net diffusion rate depends directly on the steepness of the concentration gradient.
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