facilitated diffusion

Examples of facilitated diffusion in the following topics:

• Transport of Electrolytes across Cell Membranes

  • Ions cannot diffuse passively through membranes; instead, their concentrations are regulated by facilitated diffusion and active transport.
  • Electrolyte ions may not be able to passively diffuse across a membrane, but may instead require special mechanisms to cross the semi-permeable membrane.
  • The mechanisms that transport ions across membranes are facilitated diffusion and active transport.
  • Facilitated diffusion of solutes occurs through protein-based channels.
  • Passive transport, such as diffusion, requires no energy as particles move along their gradient.

• Facilitated transport

  • Facilitated diffusion is a process by which molecules are transported across the plasma membrane with the help of membrane proteins.
  • Channel-mediated facilitated diffusion functions much like a bridge over a river that must raise and lower in order to allow boats to pass.
  • Unlike simple diffusion where materials pass through a membrane without the help of proteins, in facilitated transport, also called facilitated diffusion, materials diffuse across the plasma membrane with the help of membrane proteins.
  • Facilitated transport proteins shield these materials from the repulsive force of the membrane, allowing them to diffuse into the cell.
  • Channel proteins facilitate diffusion at a rate of tens of millions of molecules per second, whereas carrier proteins work at a rate of a thousand to a million molecules per second.

• Importance of Glycolysis

  • These transporters assist in the facilitated diffusion of glucose.

• The Role of Passive Transport

  • This may happen passively, as certain materials move back and forth, or the cell may have special mechanisms that facilitate transport.
  • In solutions containing more than one substance, each type of molecule diffuses according to its own concentration gradient, independent of the diffusion of other substances.
  • Many factors can affect the rate of diffusion, including, but not limited to, concentration gradient, size of the particles that are diffusing, and temperature of the system.
  • In living systems, diffusion of some substances would be slow or difficult without membrane proteins that facilitate transport.
  • Diffusion is a type of passive transport.

• The Plasma Membrane and the Cytoplasm

  • During this type of transport, materials move by simple diffusion or by facilitated diffusion through the membrane, down their concentration gradient.
  • Water passes through the membrane in a diffusion process called osmosis.
  • Osmosis is the diffusion of water through a semi-permeable membrane down its concentration gradient.
  • Water molecules will diffuse out of the hypotonic solution and into the hypertonic solution (unless acted upon by hydrostatic forces).
  • Osmosis is the diffusion of water through a semipermeable membrane down its concentration gradient.

• Osmosis

  • The semipermeable membrane limits the diffusion of solutes in the water.
  • Not surprisingly, the aquaporin proteins that facilitate water movement play a large role in osmosis, most prominently in red blood cells and the membranes of kidney tubules.
  • Osmosis is a special case of diffusion.
  • However, only the material capable of passing through the membrane will diffuse through it.
  • In this example, the solute cannot diffuse through the membrane, but the water can.

• Skin, Gills, and Tracheal Systems

  • A dense network of capillaries lies just below the skin, facilitating gas exchange between the external environment and the circulatory system.
  • The respiratory surface must be kept moist in order for the gases to dissolve and diffuse across cell membranes.
  • In animals that contain coelomic fluid instead of blood, oxygen diffuses across the gill surfaces into the coelomic fluid.
  • As a result, oxygen molecules diffuse from water (high concentration) to blood (low concentration) .
  • Similarly, carbon dioxide molecules diffuse from the blood (high concentration) to water (low concentration).

• Diffusion

  • Diffusion is a passive process of transport.
  • Materials move within the cell's cytosol by diffusion, and certain materials move through the plasma membrane by diffusion.
  • Diffusion expends no energy.
  • Mass of the molecules diffusing: Heavier molecules move more slowly; therefore, they diffuse more slowly.
  • If the medium is less dense, diffusion increases.

• The Respiratory System and Direct Diffusion

  • As animal size increases, diffusion distances increase and the ratio of surface area to volume drops.
  • Diffusion is a slow, passive transport process.
  • Their cells are kept moist so that gases diffuse quickly via direct diffusion.
  • Flatworms are small, literally flat worms, which ‘breathe' through diffusion across the outer membrane .
  • This flatworm's process of respiration works by diffusion across the outer membrane.

• Limiting Effects of Diffusion on Size and Development

  • The exchange of nutrients and wastes between a cell and its watery environment occurs through the process of diffusion.
  • Diffusion is effective over a specific distance and limits the size that an individual cell can attain.
  • If the cell is too large, then diffusion is ineffective at completing all of these tasks.
  • The larger the size of the sphere, or animal, the less surface area for diffusion it possesses.
  • This has an effect on diffusion because it relies on the surface area of a cell: as a cell gets bigger, diffusion becomes less efficient.