diffusion

Examples of diffusion in the following topics:

• 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.

• The Role of Passive Transport

  • Passive transport, such as diffusion and osmosis, moves materials of small molecular weight across membranes.
  • 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 substances in and out of cells is mediated by the plasma membrane.
  • Diffusion is a type of passive transport.

• 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.

• Osmosis

  • While diffusion transports materials across membranes and within cells, osmosis transports only water across a membrane.
  • The semipermeable membrane limits the diffusion of solutes in the water.
  • 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

  • The respiratory surface must be kept moist in order for the gases to dissolve and diffuse across cell membranes.
  • When water passes over the gills, the dissolved oxygen in the water rapidly diffuses across the gills into the bloodstream.
  • 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).

• Selective Permeability

  • The hydrophobic and hydrophilic regions of plasma membranes aid the diffusion of some molecules and hinder the diffusion of others.
  • Molecules of oxygen and carbon dioxide have no charge and so pass through membranes by simple diffusion.
  • Describe how membrane permeability, concentration gradient, and molecular properties affect biological diffusion rates.

• 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.
  • A concentration gradient exists that would allow these materials to diffuse into the cell without expending cellular energy.
  • Others are carrier proteins which bind with the substance and aid its diffusion through the membrane.

• Synaptic Transmission

  • Synaptic transmission is a chemical event which is involved in the transmission of the impulse via release, diffusion, receptor binding of neurotransmitter molecules and unidirectional communication between neurons.
  • The chemical event is involved in the transmission of the impulse via release, diffusion, receptor binding of neurotransmitter molecules and unidirectional communication between neurons.
  • The neurotransmitter diffuses across the synaptic cleft, binding to receptor proteins on the postsynaptic membrane.
  • Third, diffusion of the neurotransmitter as it moves away from the synapse.
  • The neurotransmitter diffuses across the synaptic cleft and binds to ligand-gated ion channels in the postsynaptic membrane, resulting in a localized depolarization or hyperpolarization of the postsynaptic neuron.