Facilitated diffusion

Definition

Facilitated diffusion is a process by which molecules move across a cell membrane through protein channels or carriers without the input of energy. This passive transport mechanism allows specific substances, such as ions and polar molecules, to cross the membrane more efficiently than they would by simple diffusion, often driven by concentration gradients. The connection to Fick's laws of diffusion highlights how facilitated diffusion is influenced by concentration differences and can be mathematically described in terms of flux and permeability.

5 Must Know Facts For Your Next Test

1. Facilitated diffusion does not require energy (ATP) because it relies on the natural movement of molecules from areas of higher concentration to lower concentration.
2. The process is highly specific, meaning that only certain molecules can be transported via specific channels or carrier proteins.
3. Fick's first law of diffusion describes how the rate of diffusion is proportional to the concentration gradient, which is relevant in understanding how facilitated diffusion operates.
4. Facilitated diffusion can be saturated when all available carrier proteins are occupied, limiting the rate at which molecules can be transported.
5. Examples of substances that utilize facilitated diffusion include glucose and ions such as Na+, K+, and Ca2+.

Review Questions

• How does facilitated diffusion differ from simple diffusion in terms of specificity and energy requirements?
  • Facilitated diffusion differs from simple diffusion primarily in its specificity and energy requirements. While simple diffusion allows any molecule to passively move across a membrane based solely on concentration gradients, facilitated diffusion involves specific carrier proteins or channels that only transport particular molecules. Additionally, both processes are passive and do not require energy, but facilitated diffusion is faster and more efficient for certain substances due to the presence of specialized transport mechanisms.
• Discuss the role of carrier proteins in facilitated diffusion and their significance in maintaining cellular function.
  • Carrier proteins play a critical role in facilitated diffusion by binding specific molecules and transporting them across the cell membrane. Their significance lies in their ability to ensure that essential nutrients, ions, and other substances can enter or exit the cell efficiently, which is vital for maintaining cellular homeostasis. By allowing selective permeability, carrier proteins help regulate internal conditions despite fluctuations in external environments, ultimately supporting various cellular processes.
• Evaluate the implications of facilitated diffusion saturation on cellular transport mechanisms and overall homeostasis.
  • The saturation of facilitated diffusion can significantly impact cellular transport mechanisms and overall homeostasis. When all available carrier proteins are occupied, any further increase in substrate concentration will not lead to an increase in transport rate. This limitation can affect how efficiently cells take up essential nutrients or expel waste products, potentially leading to imbalances that disrupt cellular functions. Understanding this saturation is crucial for comprehending how cells regulate their internal environments and respond to changes in their surroundings.

Related terms

Selective permeability: The ability of a cell membrane to allow certain substances to pass while restricting others, crucial for maintaining cellular homeostasis.

Carrier proteins: Proteins that bind to specific molecules and undergo conformational changes to transport them across the cell membrane during facilitated diffusion.

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