Facilitated diffusion

Definition

Facilitated diffusion is a passive transport process where molecules move across a cell membrane through specialized protein channels or carriers, allowing substances that cannot easily cross the lipid bilayer to enter or exit the cell. This mechanism is essential for maintaining cellular homeostasis, as it enables the selective transport of ions and polar molecules without the expenditure of energy.

5 Must Know Facts For Your Next Test

1. Facilitated diffusion does not require energy input, making it a form of passive transport.
2. Specificity of transport proteins allows for selective passage of certain molecules, such as glucose and ions.
3. Facilitated diffusion can occur through two main types of proteins: channel proteins, which create pores in the membrane, and carrier proteins, which change shape to transport molecules.
4. The rate of facilitated diffusion can be affected by factors such as temperature, the number of available transport proteins, and the size or charge of the molecule being transported.
5. This process plays a crucial role in various physiological functions, including nutrient uptake and ion balance within cells.

Review Questions

• How do transport proteins facilitate the process of facilitated diffusion across a cell membrane?
  • Transport proteins are crucial for facilitated diffusion as they provide specific pathways for certain molecules to cross the cell membrane. Channel proteins form pores that allow ions or small polar molecules to pass through, while carrier proteins undergo conformational changes to bind and transport larger molecules like glucose. This specialization ensures that substances can move efficiently without needing energy, relying instead on their concentration gradients.
• Analyze the role of concentration gradients in facilitated diffusion and discuss how they influence molecular movement across membranes.
  • Concentration gradients are essential for facilitating molecular movement during facilitated diffusion. Molecules naturally move from areas of higher concentration to areas of lower concentration until equilibrium is reached. This gradient drives the passive transport process, allowing molecules to enter or exit cells without energy expenditure. The effectiveness of this process relies on the presence and activity of specific transport proteins that recognize and assist particular molecules in crossing the membrane.
• Evaluate the significance of facilitated diffusion in maintaining cellular homeostasis and its impact on physiological processes.
  • Facilitated diffusion is vital for maintaining cellular homeostasis as it allows cells to control their internal environments by selectively transporting essential nutrients and ions. This process impacts various physiological functions, such as glucose uptake in muscle cells during exercise or ion balance in nerve cells during signaling. By regulating the movement of these substances, facilitated diffusion plays a key role in ensuring that cells can respond effectively to changes in their environment and maintain overall health.

Related terms

Transport proteins: Proteins that assist in the movement of substances across a cell membrane, including channels and carriers that facilitate diffusion.

Concentration gradient: The difference in the concentration of a substance across a space, which drives the movement of molecules during facilitated diffusion from high to low concentration.

Membrane potential: The electric potential difference across a cell membrane, which influences the movement of charged particles during facilitated diffusion.