- simple diffusion
- facilitated diffusion
- osmosis

Types of Passive Transport

Passive transport is a mode of membrane transport where molecules move along their concentration gradient, from an area of higher concentration to an area of lower concentration. Unlike active transport, this process does not require the cell to expend energy.

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A primary function of the plasma membrane is controlling the transport of molecules into and out of the cell. This continuous regulation allows the cell to maintain internal conditions within a specific range, regardless of changes in the external environment. Cells utilize various modes of transport, broadly categorized into passive and active mechanisms, to move substances across the plasma membrane.

Membrane Transport

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Active transport occurs when cells move molecules across the plasma membrane against their concentration gradients, effectively moving them "uphill" from an area of lower concentration to an area of higher concentration. This process requires an input of energy, typically adenosine triphosphate (ATP) or other forms of energy. Due to this significant energy requirement, the membrane structures that facilitate active transport are often referred to as "pumps."

Active Transport

Passive Transport

Group translocation is a mechanism used to transport substances into bacterial cells. As a molecule is moved against its concentration gradient into the cell, it is chemically modified, which prevents it from needing to be transported against an unfavorable gradient once inside. A common example is the bacterial phosphotransferase system, a series of carriers that phosphorylates sugars like glucose as they enter. Because this phosphorylation is already required during the early stages of sugar metabolism, the system is considered energy neutral.

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