Facilitated diffusion is used to transport
A) sugars and amino acids.
B) H2O and O2.
C) CO2 and O2.
D) CO2 and H2O.
E) sugars and H2O.
The Correct Answer and Explanation is:
The correct answer is A) sugars and amino acids.
Explanation:
Facilitated diffusion is a type of passive transport that allows substances to cross membranes with the assistance of special proteins. Unlike simple diffusion, which relies solely on the concentration gradient and the lipid bilayer’s permeability, facilitated diffusion employs carrier proteins or channel proteins to transport specific molecules that cannot readily pass through the membrane due to their size, polarity, or charge.
- Mechanism of Facilitated Diffusion: In facilitated diffusion, molecules bind to specific carrier proteins that change shape to shuttle the molecules across the cell membrane. This process does not require energy (ATP) because it moves substances down their concentration gradient, from areas of higher concentration to areas of lower concentration. The specificity of the carrier proteins ensures that only certain substances, such as sugars (like glucose) and amino acids, can be transported this way.
- Substances Involved: Sugars and amino acids are vital nutrients for cells. Glucose, for example, is transported into cells via glucose transporters, while amino acids utilize various specific transporters based on their side chains (polar, nonpolar, etc.). This targeted transport is crucial for cellular metabolism and function.
- Comparison with Other Options: Other options like H2O and O2 (B), CO2 and O2 (C), CO2 and H2O (D), and sugars and H2O (E) are not primarily transported through facilitated diffusion. While water can move via specialized channels called aquaporins, and gases like O2 and CO2 diffuse directly through the lipid bilayer due to their small size and nonpolar nature, they do not rely on facilitated diffusion.
In summary, facilitated diffusion is essential for transporting larger and polar molecules, particularly sugars and amino acids, into cells, allowing them to be utilized for energy production, growth, and repair.