Which one of the following statements is INCORRECT about facilitated diffusion?
(1) Its rate is higher than simple diffusion.
(2) The partition coefficient of the solute is irrelevant for it.
(3) It can be saturated at high concentration of the solute.
(4) It works against the concentration gradient.
Which One of the Following Statements Is INCORRECT About Facilitated Diffusion?
Facilitated diffusion is a vital biological process that enables cells to transport substances across membranes using protein channels or carriers, without expending energy. It plays an essential role in maintaining homeostasis and regulating the internal environment of the cell.
Here’s a commonly asked question in biology exams:
Which one of the following statements is INCORRECT about facilitated diffusion?
Options:
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Its rate is higher than simple diffusion.
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The partition coefficient of the solute is irrelevant for it.
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It can be saturated at high concentration of the solute.
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It works against the concentration gradient.
✅ Correct Answer: (4) It works against the concentration gradient. (INCORRECT statement)
What Is Facilitated Diffusion?
Facilitated diffusion is a type of passive transport in which molecules move across a biological membrane via specific transport proteins, from an area of high concentration to low concentration, without the use of energy (ATP).
Key Characteristics of Facilitated Diffusion
Let’s analyze each of the provided statements and determine which are correct and which is incorrect:
✅ (1) Its rate is higher than simple diffusion.
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True: Facilitated diffusion is faster than simple diffusion for specific solutes because transport proteins provide a more efficient pathway across the membrane.
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Example: Glucose enters cells much faster through GLUT transporters than by passive diffusion alone.
✅ (2) The partition coefficient of the solute is irrelevant for it.
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True: The partition coefficient reflects how well a substance dissolves in lipids (fat vs. water solubility), which is important in simple diffusion across the lipid bilayer.
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In facilitated diffusion, the solute interacts with proteins, not the lipid membrane, making the partition coefficient irrelevant.
✅ (3) It can be saturated at high concentration of the solute.
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True: Facilitated diffusion involves carrier proteins, which can become saturated when all binding sites are occupied. This leads to a maximum transport rate (Vmax), similar to enzyme kinetics.
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This is a hallmark of facilitated transport and a key difference from simple diffusion.
❌ (4) It works against the concentration gradient.
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False: This is the incorrect statement.
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Facilitated diffusion does NOT work against the concentration gradient. It only transports molecules down their concentration gradient (from high to low).
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Movement against the gradient requires active transport, which involves energy (usually ATP) and different transport mechanisms like pumps.
Summary Table
| Statement | Correct/Incorrect | Explanation |
|---|---|---|
| 1. Faster than simple diffusion | ✅ Correct | Transport proteins increase speed |
| 2. Partition coefficient is irrelevant | ✅ Correct | Doesn’t depend on lipid solubility |
| 3. Can be saturated | ✅ Correct | Follows transport protein limits |
| 4. Works against concentration gradient | ❌ Incorrect | Requires active transport |
Conclusion
The incorrect statement about facilitated diffusion is:
(4) It works against the concentration gradient.
Facilitated diffusion is a passive transport mechanism that operates only down a concentration gradient. Unlike active transport, it does not require energy and depends on specific transport proteins for selective movement of molecules like glucose, amino acids, and ions.
Understanding this distinction is critical for students, researchers, and anyone interested in cell biology or physiology. Mastering the principles of molecular transport helps explain how nutrients enter cells, how signals are transmitted, and how the body maintains internal balance.
