Facilitated diffusion differs from ordinary diffusion in that __.
Question 7 ?options:
the rate of facilitated diffusion is limited by the number of available carrier molecules
facilitated diffusion never eliminates the concentration gradient
facilitated diffusion moves molecules from an area of high concentration to an area of low concentration
facilitated diffusion expends no ATP
The Correct Answer and Explanation is :
Correct Answer:
The rate of facilitated diffusion is limited by the number of available carrier molecules.
Explanation:
Facilitated diffusion is a type of passive transport that allows specific molecules to cross a biological membrane with the help of carrier proteins or channel proteins. It differs from ordinary diffusion in several key ways, as outlined below:
- Carrier and Channel Proteins:
- Unlike ordinary diffusion, which involves the free movement of molecules through the membrane without assistance, facilitated diffusion requires specialized proteins. These proteins selectively bind to specific molecules, such as glucose or ions, and transport them across the membrane.
- Rate Limitation by Carrier Molecules:
- The availability of carrier or channel proteins limits the rate of facilitated diffusion. When all the carrier proteins are occupied, the transport rate reaches a maximum, known as the saturation point. This contrasts with simple diffusion, where the rate continues to increase with higher concentration gradients.
- Selective Transport:
- Facilitated diffusion is highly selective due to the specificity of carrier proteins. Each carrier protein is tailored to transport only certain molecules or ions, making this process more targeted than simple diffusion.
- Energy Use:
- Like ordinary diffusion, facilitated diffusion does not require cellular energy (ATP). The process relies on the concentration gradient, where molecules move from areas of high concentration to low concentration.
- Elimination of the Gradient:
- Facilitated diffusion can, over time, eliminate the concentration gradient if the process continues without interruptions, which is a similarity to ordinary diffusion.
In summary, the defining characteristic of facilitated diffusion is its reliance on carrier proteins, which limits its rate of transport based on the number of these proteins available. This distinguishes it from ordinary diffusion, where transport is not constrained by protein availability.