Facilitated diffusion

Definition

Facilitated diffusion is a process of passive transport that allows substances to cross membranes with the assistance of special proteins, such as carrier proteins and channels. This mechanism is crucial for transporting polar and charged molecules, like glucose and ions, across the hydrophobic lipid bilayer of cells without the use of energy, thereby ensuring that essential nutrients and signals can enter or exit the cell efficiently.

5 Must Know Facts For Your Next Test

1. Facilitated diffusion is a passive process, meaning it does not require ATP or any energy input to move substances across the membrane.
2. Carrier proteins change shape to transport specific molecules across the membrane, while channel proteins provide passages for ions and small molecules to flow through.
3. This process is selective; only certain molecules can utilize facilitated diffusion based on their size, charge, and the specific transport protein available.
4. Facilitated diffusion plays a critical role in maintaining cellular homeostasis by regulating the concentration of important molecules inside the cell.
5. Factors such as temperature and concentration gradient can affect the rate of facilitated diffusion, as higher temperatures and greater concentration differences typically increase the transport rate.

Review Questions

• How does facilitated diffusion differ from simple diffusion in terms of mechanisms and efficiency for transporting substances?
  • Facilitated diffusion differs from simple diffusion primarily in that it requires specific transport proteins to assist in moving molecules across the membrane. While simple diffusion allows substances to move directly through the lipid bilayer based on concentration gradients, facilitated diffusion utilizes carrier and channel proteins to transport polar or charged substances that cannot easily cross the hydrophobic membrane. This mechanism increases efficiency for these specific molecules, ensuring they reach equilibrium more rapidly than they would through simple diffusion.
• In what ways do transport proteins enhance the process of facilitated diffusion compared to other forms of membrane transport?
  • Transport proteins enhance facilitated diffusion by providing specificity and speed for particular molecules. Carrier proteins undergo conformational changes to bind and release their target substrates, while channel proteins create hydrophilic pathways for ions and small solutes. This specificity allows cells to control which substances enter or exit efficiently, unlike passive diffusion where all small nonpolar molecules can move freely. Additionally, transport proteins can increase the rate of transport significantly under conditions where passive diffusion would be too slow.
• Evaluate the importance of facilitated diffusion in maintaining cellular homeostasis and how it interacts with active transport mechanisms.
  • Facilitated diffusion is crucial for maintaining cellular homeostasis by enabling cells to selectively import essential nutrients like glucose and export waste products without expending energy. It operates in conjunction with active transport mechanisms, which require energy to move substances against their concentration gradients. The two processes work together to ensure that cells have adequate supplies of vital molecules while removing excess ions or waste products. By balancing passive facilitated diffusion with active transport, cells can maintain optimal internal environments necessary for proper physiological function.

Related terms

Transport proteins: Proteins that assist in the movement of substances across a cell membrane, including both facilitated diffusion and active transport mechanisms.

Diffusion:

The movement of molecules from an area of higher concentration to an area of lower concentration, which can occur directly through the lipid bilayer or through facilitated diffusion.

Membrane permeability: A property that describes how easily substances can pass through a membrane, which is influenced by factors such as molecular size, charge, and the presence of transport proteins.