14.2 Cell Transport

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Active Transport

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The movement of molecules across a cell membrane from low to high concentration using energy (usually ATP). It helps cells absorb nutrients even when they’re scarce outside.

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Osmosis

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The passive movement of water molecules through a semipermeable membrane from an area of low solute concentration to high solute concentration.

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Facilitated Diffusion

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A type of passive transport where molecules move across a membrane with the help of transport proteins, without using energy.

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Concentration Gradient

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A difference in the concentration of a substance across a space or membrane. Molecules naturally move from high to low concentration.

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Co-Transport

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A transport method where two substances move across a membrane together—one down its gradient, helping the other move against its gradient.

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Lipid Bilayer

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The double-layered structure of the cell membrane made of phospholipids. It has hydrophilic heads facing out and hydrophobic tails facing in.

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Hydrophobic

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Describes molecules that repel water. These are usually nonpolar and found in the inner part of the cell membrane.

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Hydrophilic

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Describes molecules that attract and dissolve in water. These are usually polar and found on the outer surfaces of membranes.

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Molecular Transport

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The process by which small molecules and ions are moved across a cell membrane with the help of specialized proteins, often requiring energy to go against their concentration gradient.

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Bulk Transport

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The movement of large particles or large quantities of substances into or out of a cell using vesicles. Includes endocytosis and exocytosis and uses energy.