Cell Membrane

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Plasma Membrane Noun

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[plaz-muh mem-breyn]

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Plasma Membrane

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The semipermeable barrier surrounding a cell, controlling substance passage and separating the cell from its external environment.

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Example: This diagram shows the plasma membrane is a flexible barrier with embedded proteins that control what substances can pass into or out of the cell.

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Homeostasis Noun

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[hoh-mee-oh-stey-sis]

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Homeostasis

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The tendency of a biological system to maintain a stable, relatively constant internal environment to ensure proper functioning.

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Example: This diagram shows a red blood cell delivering oxygen to body cells, a process that maintains stable oxygen levels, which is an example of homeostasis.

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Semipermeable Adjective

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[sem-ee-pur-mee-uh-buhl]

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Semipermeable

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A property of a membrane that allows certain molecules or ions to pass through it by diffusion but not others.

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Example: This diagram shows a semipermeable cell membrane, which acts as a selective barrier, allowing certain molecules like water to pass through into the cell.

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Phospholipid Noun

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[fos-foh-lip-id]

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Phospholipid

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A lipid molecule with a hydrophilic head and two hydrophobic tails that is the main component of cell membranes.

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Example: This diagram shows how a phospholipid has a water-loving (hydrophilic) head and a water-fearing (hydrophobic) tail, causing them to form a lipid bilayer.

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Hydrophilic Adjective

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[hy-dro-fil-ik]

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Hydrophilic

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Describes molecules or parts of molecules that are chemically attracted to, and tend to be dissolved by, water.

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Example: This diagram shows a cell membrane's phospholipid bilayer, where the round 'hydrophilic heads' face outwards because they are attracted to water.

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Hydrophobic Adjective

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[hy-dro-foh-bik]

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Hydrophobic

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Describes molecules or parts of molecules that repel or fail to mix with water, tending to be nonpolar.

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Example: This diagram shows that hydrophobic ('water-fearing') tails of molecules cluster together to avoid water, surrounding an oil droplet, a key principle in cell membrane formation.

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Phospholipid Bilayer Noun

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[fos-foh-lip-id bahy-ley-er]

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Phospholipid Bilayer

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The double layer of phospholipid molecules that forms the basic structural framework of all cell membranes.

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Example: This diagram shows the phospholipid bilayer as two layers of molecules, forming the basic structure of the cell membrane, which also contains various proteins.

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Fluid Mosaic Model Noun

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[floo-id moh-zey-ik mod-l]

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Fluid Mosaic Model

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A model describing the cell membrane as a dynamic structure with proteins and lipids free to move laterally.

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Example: The cell membrane is a fluid mosaic, with various proteins and carbohydrates embedded or attached to a flexible, double layer of phospholipids.

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Passive Transport Noun

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[pas-iv trans-port]

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Passive Transport

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The movement of substances across a cell membrane from high to low concentration without the use of cellular energy.

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Example: This image shows molecules moving across a cell membrane over time, from an area of high concentration to an area of low concentration, without using energy.

Front

Diffusion Noun

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[dih-fyoo-zhun]

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Diffusion

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The net passive movement of particles from a region of higher concentration to a region of lower concentration.

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Example: Carbon dioxide (CO2) molecules move from an area of high concentration to an area of low concentration, passing directly through the cell membrane.