passive transport

(noun)

A movement of biochemicals and other atomic or molecular substances across membranes that does not require an input of chemical energy.

Related Terms

Examples of passive transport in the following topics:

  • 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.

  • Transport of Electrolytes across Cell Membranes

    • Ions cannot diffuse passively through membranes; instead, their concentrations are regulated by facilitated diffusion and active transport.
    • The mechanisms that transport ions across membranes are facilitated diffusion and active transport.
    • All movement can be classified as passive or active.
    • Passive transport, such as diffusion, requires no energy as particles move along their gradient.
    • Active transport requires additional energy as particles move against their gradient.

  • Facilitated transport

    • Facilitated transport is a type of passive transport.
    • The integral proteins involved in facilitated transport are collectively referred to as transport proteins; they function as either channels for the material or carriers.
    • Channels are specific for the substance that is being transported.
    • Channel and carrier proteins transport material at different rates.
    • Channel proteins transport much more quickly than do carrier proteins.

  • 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.
    • In contrast to passive transport, active (energy-requiring) transport is the movement of substances across the membrane using energy from adenosine triphosphate (ATP).
    • Active transport may take place with the help of protein pumps or through the use of vesicles.
    • Another form of this type of transport is endocytosis, where a cell envelopes extracellular materials using its cell membrane.
    • This is where a cell exports material using vesicular transport.

  • 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.
    • The cell employs a number of transport mechanisms that involve biological membranes:
    • Passive osmosis and diffusion: transports gases (such as O2 and CO2) and other small molecules and ions
    • Transmembrane protein channels and transporters: transports small organic molecules such as sugars or amino acids
    • Endocytosis: transports large molecules (or even whole cells) by engulfing them

  • Absorption in the Small Intestine

    • The epithelial cells of the villi transport nutrients from the lumen of the intestine into these capillaries (amino acids and carbohydrates) and lacteals (lipids).
    • The absorbed substances are transported via the blood vessels to different organs of the body where they are used to build complex substances such as the proteins required by our body.
    • Absorption of the majority of nutrients takes place in the jejunum, with the following notable exceptions: iron is absorbed in the duodenum; vitamin B12 and bile salts are absorbed in the terminal ileum; water and lipids are absorbed by passive diffusion throughout the small intestine; sodium bicarbonate is absorbed by active transport and glucose and amino acid co-transport; and fructose is absorbed by facilitated diffusion.

  • Tubular Reabsorption

    • Tubular reabsorption is the process by which solutes and water are removed from the tubular fluid and transported into the blood.
    • Reabsorption in the nephron may be either a passive or active process, and the specific permeability of the each part of the nephron varies considerably in terms of amount and type of substance reabsorbed.
    • Passive Diffusion-passing through plasma membranes of the kidney epithelial cells by concentration gradients.
    • Active Transport-membrane bound ATPase pumps (such as NA+/K+ ATPase pumps) with carrier proteins carry substances across the plasma membranes of the kidney epithelial cells by consuming ATP.
    • Water can follow other molecules that are actively transported, particularly glucose and sodium ions in the nephron.

  • Immunological Memory

    • Immunological memory can either be in active long-term memory or passive short-term memory.
    • Thus, the mother protects the infant through several layers of passive protection.
    • During pregnancy, IgG, a certain isotype of antibody, is transported to the baby from the mother through the placenta, so even babies have high levels of antibodies that have similar antigen specificities as the mother.
    • Since the fetus isn't making any memory cells or antibodies, it is called passive immunity.
    • The passive immunity is short-lived, ranging from a couple days to a couple months.

  • Electrochemical Gradient

    • Active transport mechanisms, collectively called pumps, work against electrochemical gradients.
    • Active transport maintains concentrations of ions and other substances needed by living cells in the face of these passive movements.
    • Two mechanisms exist for the transport of small-molecular weight material and small molecules.
    • Secondary active transport describes the movement of material that is due to the electrochemical gradient established by primary active transport that does not directly require ATP.
    • All of these transporters can also transport small, uncharged organic molecules like glucose.

  • Avoiding Passive Voice

    • A way to focus your sentences on action and actors is to use the active voice rather than the passive voice.
    • For example, "the changes were recommended by the consultant" is an example of the passive voice.
    • Research shows that readers comprehend active sentences more rapidly than passive ones.
    • In the passive voice, a sentence can describe an action without telling who did it.
    • Using the passive voice in your writing can obscure the meaning of your message.