Definition

Noun: The movement of a substance across a cell membrane, driven by diffusion or osmosis, without the expenditure of cellular energy (ATP). It relies on the natural kinetic energy of molecules moving down their concentration gradient, from an area of higher concentration to an area of lower concentration.

Usage

This term is used specifically in the context of cellular biology and physiology to describe a fundamental process of cellular exchange. It contrasts directly with "active transport."

Examples

• Simple Sentence: Oxygen enters cells by passive transport.
• In Context: The absorption of water into plant root hairs occurs through passive transport, specifically osmosis.
• Comparative: Unlike active transport, passive transport does not require the cell to use energy.

Advanced Usage

• Scientific Description: Passive transport is a critical mechanism for maintaining homeostasis, allowing for the efficient uptake of essential molecules and the release of waste products without energy cost to the cell.
• In Research: The study focused on the rate of passive transport of the solute across the lipid bilayer.

Variants and Related Words

• Diffusion (n): The specific type of passive transport where particles spread out from an area of high concentration to an area of low concentration.
• Osmosis (n): The passive transport of water across a selectively permeable membrane.
• Facilitated Diffusion (n): A type of passive transport that uses membrane proteins to help substances cross the membrane without energy use.
• Passively (adv): In a manner relating to passive transport. (e.g., The ion moves through the channel protein.)

Synonyms

• Diffusion (in its general sense)
• Non-active transport

Antonyms

• Active transport (n): Energy-requiring movement of substances against a concentration gradient.

Related Phrases

• Concentration gradient: The difference in concentration that drives passive transport.
• Selectively permeable membrane: The barrier through which passive transport occurs.
• Down its gradient: A common phrase describing the direction of movement in passive transport (e.g., The molecule moved ).

Noun

1. transport of a substance across a cell membrane by diffusion; expenditure of energy is not required