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Membranes and transport

The plasma membrane

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Fluid mosaic model of cell membranes

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Structure of the plasma membrane

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Diffusion and osmosis

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Diffusion - Introduction

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Concentration gradients

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Hypotonic, isotonic, and hypertonic solutions (tonicity)

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Osmosis and tonicity

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Diffusion and osmosis

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Diffusion, osmosis, and tonicityGet 5 of 7 questions to level up!

Passive transport

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Passive transport and selective permeability

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Facilitated diffusion

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Diffusion and passive transport

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Passive transportGet 3 of 4 questions to level up!

Active transport

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Sodium potassium pump

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Electrochemical gradients and secondary active transport

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Uniporters, symporters and antiporters

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Active transport

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Active transportGet 3 of 4 questions to level up!

Bulk transport

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Endocytosis, phagocytosis, and pinocytosis

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Bulk transportGet 3 of 4 questions to level up!

About this unit

How do the cells in your body define their boundaries (and control what comes in or goes out)? As it turns out, cells have a sophisticated and flexible barrier, the plasma membrane, and a wide array of strategies for transporting molecules in and out. Learn more about what the membrane's made of and how different types of molecules move across it.