Active and Passive Transport

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Homeostasis Noun

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[ho-mee-o-stay-sis]

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Homeostasis

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The process by which a cell or organism maintains a stable, constant internal environment despite changes in external conditions.

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Example: This diagram shows how red blood cells transport oxygen from the lungs to body cells, a process essential for maintaining homeostasis through passive transport (diffusion).

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Cell Membrane Noun

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[sel mem-brayn]

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Cell Membrane

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The semi-permeable barrier surrounding a cell, controlling which substances can enter or leave to maintain internal balance.

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Example: This diagram shows the cell membrane is a barrier with embedded proteins. The ion channel protein creates a pore, or tunnel, for specific substances to pass through.

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Semi-Permeable Adjective

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

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Semi-Permeable

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A property of a membrane that allows certain molecules or ions to pass through it but prevents the passage of others.

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Example: This diagram shows the lipid bilayer, the structure that forms a semi-permeable cell membrane, with its water-loving heads and water-fearing tails.

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Receptor Molecule Noun

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[ri-sep-ter mol-i-kyool]

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Receptor Molecule

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A protein in the cell membrane that recognizes, receives, and responds to specific external chemical signals from other cells.

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Example: A specific signaling molecule binds to a receptor molecule on the cell surface, causing the receptor to change shape and open a channel for ions to pass through.

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

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Example: Particles move from an area of high concentration to an area of low concentration across a membrane, which does not require energy.

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Concentration Gradient Noun

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[kon-sen-tray-shun gray-dee-ent]

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Concentration Gradient

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The difference in the concentration of a substance between two areas, which determines the direction of molecular movement.

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Example: This image shows particles (dye) moving from an area of high concentration to an area of low concentration, which demonstrates the effect of a concentration gradient.

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Diffusion Noun

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[di-fyoo-zhun]

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Diffusion

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The passive movement of molecules from an area of higher concentration to an area of lower concentration until equilibrium is reached.

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Example: Particles move from an area of high concentration to an area of low concentration across a cell membrane, a process that does not require energy.

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Facilitated Diffusion Noun

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[fuh-sil-i-tay-tid di-fyoo-zhun]

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Facilitated Diffusion

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A type of passive transport where molecules move across the cell membrane with the help of specific protein channels.

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Example: Molecules move from a high concentration area to a low concentration area across the cell membrane by passing through a special protein channel.

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Osmosis Noun

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[oz-mo-sis]

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Osmosis

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The specific diffusion of water molecules across a selectively permeable membrane from high to low water concentration.

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Example: Water molecules (solvent) move across a semi-permeable membrane from an area of high concentration to an area of low concentration, while larger solute molecules cannot pass.

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Active Transport Noun

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[ak-tiv trans-port]

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Active Transport

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The movement of molecules across a cell membrane against their concentration gradient, which requires the use of cellular energy.

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Example: A cell uses energy (ATP) to move substances through a protein channel from an area of low concentration to an area of high concentration.