passive diffusion

Examples of passive 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.
  • Water passes through semi-permeable membranes by passive diffusion, moving along a concentration gradient and equalizing the concentration on either side of the membrane.
  • Electrolyte ions may not be able to passively diffuse across a membrane, but may instead require special mechanisms to cross the semi-permeable membrane.
  • All movement can be classified as passive or active.
  • Passive transport, such as diffusion, requires no energy as particles move along their gradient.

• The Role of Passive Transport

  • Passive transport, such as diffusion and osmosis, moves materials of small molecular weight across membranes.
  • The most direct forms of membrane transport are passive.
  • In passive transport, substances move from an area of higher concentration to an area of lower concentration .
  • The passive forms of transport, diffusion and osmosis, move materials of small molecular weight across membranes.
  • Diffusion is a type of passive transport.

• Diffusion

  • Diffusion is a process of passive transport in which molecules move from an area of higher concentration to one of lower concentration.
  • 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.

• Kidney Function and Physiology

  • All solutes in the glomerular capillaries, including sodium ions and negatively and positively charged ions, pass through by passive diffusion; the only exception is macromolecules such as proteins.
  • Almost all nutrients are reabsorbed; this occurs either by passive or active transport.

• 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.

• Components of Plasma Membranes

  • The movement of a substance across the selectively permeable plasma membrane can be either "passive"—i.e., occurring without the input of cellular energy—or "active"—i.e., its transport requires the cell to expend energy.
  • Passive osmosis and diffusion: transports gases (such as O2 and CO2) and other small molecules and ions

• Facilitated transport

  • Facilitated diffusion is a process by which molecules are transported across the plasma membrane with the help of membrane proteins.
  • Facilitated transport is a type of passive transport.
  • 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.

• The Plasma Membrane and the Cytoplasm

  • Passive (non-energy requiring) transport is the movement of substances across the membrane without the expenditure of cellular energy.
  • 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.
  • In contrast to passive transport, active (energy-requiring) transport is the movement of substances across the membrane using energy from adenosine triphosphate (ATP).

• Types of Breathing

  • As the diaphragm relaxes, air passively leaves the lungs .
  • As the intercostal muscles relax, air passively leaves the lungs.
  • The other means of breathing for amphibians is diffusion across the skin.
  • To aid this diffusion, amphibian skin must remain moist.
  • Oxygenated air, taken in during inhalation, diffuses across the surface of the lungs into the bloodstream, while carbon dioxide diffuses from the blood into the lungs and is expelled during exhalation.

• Malpighian Tubules of Insects

  • Metabolic wastes, such as urea and amino acids, freely diffuse into the tubules, while ions are transported through active pump mechanisms.
  • There are exchange pumps lining the tubules which actively transport H+ ions into the cell and K+ or Na+ ions out; water passively follows to form urine.