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6.4: Introduction to Kinds of Transport

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    What you’ll learn to do: Explain how substances are directly transported across a membrane

    Plasma membranes must allow certain substances to enter and leave a cell, and prevent some harmful materials from entering and some essential materials from leaving. In other words, plasma membranes are selectively permeable—they allow some substances to pass through, but not others. If they were to lose this selectivity, the cell would no longer be able to sustain itself, and it would be destroyed. Some cells require larger amounts of specific substances than do other cells; they must have a way of obtaining these materials from extracellular fluids. This may happen passively, as certain materials move back and forth, or the cell may have special mechanisms that facilitate transport. Some materials are so important to a cell that it spends some of its energy, hydrolyzing adenosine triphosphate (ATP), to obtain these materials. For example, red blood cells use some of their energy doing just that. All cells spend the majority of their energy to maintain an imbalance of sodium and potassium ions between the interior and exterior of the cell.

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    • Introduction to Kinds of Transport. Authored by: Shelli Carter and Lumen Learning. Provided by: Lumen Learning. License: CC BY: Attribution
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    6.4: Introduction to Kinds of Transport is shared under a not declared license and was authored, remixed, and/or curated by LibreTexts.

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