Facilitated diffusion

Definition

Facilitated diffusion is a process by which molecules move across a cell membrane through specific transport proteins, down their concentration gradient, without the expenditure of energy. This mechanism is crucial for transporting substances that cannot freely pass through the lipid bilayer of the cell membrane, such as polar or large molecules. The process ensures that essential nutrients and ions can enter cells efficiently while maintaining homeostasis.

5 Must Know Facts For Your Next Test

1. Facilitated diffusion occurs spontaneously and does not require ATP, as it relies on the concentration gradient of the molecules being transported.
2. Specific types of transport proteins involved in facilitated diffusion include channel proteins and carrier proteins, each serving different types of molecules.
3. This process is essential for the uptake of glucose by cells, where glucose transporters facilitate its movement into the cell without using energy.
4. Facilitated diffusion can be saturated, meaning that if all available transport proteins are occupied, increasing concentrations of the substance will not increase the rate of transport.
5. Certain factors such as temperature and pH can affect the rate of facilitated diffusion by influencing protein structure and function.

Review Questions

• How does facilitated diffusion differ from simple diffusion regarding the role of transport proteins?
  • Facilitated diffusion differs from simple diffusion primarily because it requires specific transport proteins to assist in moving molecules across the cell membrane. While simple diffusion allows molecules to pass freely through the lipid bilayer based on their concentration gradient, facilitated diffusion relies on these proteins to help polar or larger molecules that cannot easily cross the lipid bilayer. Thus, transport proteins play a crucial role in selectively allowing certain substances into or out of the cell.
• Discuss how facilitated diffusion is significant for cellular function and homeostasis.
  • Facilitated diffusion is vital for cellular function as it allows cells to efficiently uptake essential nutrients, such as glucose and ions, while also helping to remove waste products. By enabling specific molecules to pass through the cell membrane without using energy, this process maintains homeostasis within cells. For example, when glucose levels are high outside the cell, facilitated diffusion allows it to enter quickly, providing energy for metabolic processes. This efficient transport mechanism is essential for overall cellular health and functionality.
• Evaluate how factors like temperature and pH impact the effectiveness of facilitated diffusion in cells.
  • Factors such as temperature and pH can significantly impact facilitated diffusion by affecting both the structure and function of transport proteins. Increased temperature may enhance molecular movement and protein flexibility, potentially speeding up the rate of transport. Conversely, extreme pH levels can denature proteins, altering their structure and impairing their ability to transport molecules effectively. Understanding these impacts is crucial for comprehending how cells adapt to varying environmental conditions and maintain optimal function through facilitated diffusion.

Related terms

Cell membrane: The cell membrane is a biological barrier that separates the interior of a cell from its external environment, regulating the movement of substances in and out of the cell.

Transport proteins: Transport proteins are specialized proteins embedded in the cell membrane that assist in the movement of substances across the membrane, either through facilitated diffusion or active transport.

Concentration gradient: A concentration gradient refers to the difference in concentration of a substance across a space, with molecules naturally moving from areas of higher concentration to areas of lower concentration during diffusion.