Facilitated diffusion

Definition

Facilitated diffusion is a passive transport mechanism that allows specific molecules or ions to cross a biological membrane with the assistance of specialized proteins. This process occurs down the concentration gradient, meaning substances move from areas of higher concentration to lower concentration, without the use of cellular energy. It plays a crucial role in maintaining cellular homeostasis, especially in eukaryotic cells where the lipid bilayer can be selectively permeable.

5 Must Know Facts For Your Next Test

1. Facilitated diffusion is specific, meaning only certain molecules can pass through the membrane via this method, usually based on size and charge.
2. This process does not require ATP or any energy input from the cell, relying instead on the natural movement of particles.
3. Facilitated diffusion is essential for transporting large polar molecules like glucose and ions such as Na+ and K+ that cannot easily cross the lipid bilayer.
4. The rate of facilitated diffusion can be affected by factors such as temperature, concentration gradient, and the number of available carrier or channel proteins.
5. If a cell is exposed to an environment with a higher concentration of a particular solute, facilitated diffusion will occur to equalize concentrations across the membrane.

Review Questions

• How does facilitated diffusion differ from simple diffusion, and why is this distinction important in cellular processes?
  • Facilitated diffusion differs from simple diffusion in that it requires specific proteins to assist in transporting molecules across the membrane. While simple diffusion allows any small nonpolar molecules to pass directly through the lipid bilayer, facilitated diffusion is selective and enables larger or polar molecules that cannot cross freely. This distinction is important because it ensures that essential nutrients like glucose can enter cells efficiently while maintaining control over what substances are allowed passage.
• Discuss the roles of channel proteins and carrier proteins in facilitated diffusion and how they contribute to the transport process.
  • Channel proteins provide a direct pathway for ions or small molecules to pass through the cell membrane. They create pores that allow specific substances to flow down their concentration gradient. On the other hand, carrier proteins bind to particular molecules and change shape to transport them across the membrane. Both types of proteins are crucial for facilitated diffusion as they ensure that vital nutrients and ions are efficiently transported into or out of cells without expending energy.
• Evaluate how facilitated diffusion maintains cellular homeostasis and its implications for overall cell function.
  • Facilitated diffusion maintains cellular homeostasis by allowing essential substances like glucose and ions to move in and out of cells according to their concentration gradients. This regulation is vital for processes such as energy production and signal transduction. When cells effectively manage their internal environment through facilitated diffusion, they can maintain optimal conditions for metabolic activities. Disruptions in this process can lead to imbalances that affect cell function and health, highlighting its importance in overall cellular operations.

Related terms

Channel proteins: Proteins that form pores in the cell membrane, allowing specific ions or molecules to pass through during facilitated diffusion.

Carrier proteins: Proteins that bind to specific substances and undergo a conformational change to shuttle these substances across the cell membrane.

Concentration gradient: The difference in concentration of a substance across a space, driving the movement of substances during passive transport.