A-F

• Brush border – A dense layer of microvilliTiny projections on the surface of epithelial cells that increase surface area for absorption. on the surface of certain cellsThe basic structural and functional units of life., increasing surface area for absorption.
• Centrioles – Cylindrical structures involved in organizing microtubules and cell division.
• Centrosomes – The region near the nucleusThe control center of the cell that contains DNA and directs cellular activities. that contains centriolesCylindrical structures involved in organizing microtubules and cell division. and helps organize the cytoskeleton A network of protein filaments that provide structure, shape, and movement to cells..
• Cilia – Hair-like projections on the surface of some cells that move fluids or particles.
• Cytoplasm – The gel-like substance within a cell that contains organellestructures within a cell that perform specialized functions. and cytosol.
• Cytoskeleton – A network of protein filaments that provide structure, shape, and movementA fundamental property of life involving motion of the body or its parts. to cells.
• Cytosol – The fluid portion of the cytoplasmThe gel-like substance within a cell that contains organelles and cytosol., excluding organelles.
• Extracellular fluid – Fluid found outside of cells, including interstitial fluidThe fluid surrounding cells within tissues. and plasmaThe liquid component of blood..
• Flagella – Long, whip-like structures used by some cells (e.g., sperm) for movement.

G-K

• G proteinA signaling protein activated by neurotransmitter receptors that triggers internal cellular response – A signaling molecule that helps transmit signals from receptorsProteins located on the surface or inside cells that bind specific molecules (e.g., neurotransmitter to intracellular pathways.
• Glycocalyx – A sugar-rich coating on the surface of cells that provides protection and cell recognition.
• Glycolipid – A lipid with a carbohydrateOrganic molecules composed of carbon, hydrogen, and oxygen, primarily used for energy. attached, playing a role in cell recognition.
• Glycoprotein – A protein with a carbohydrate chain attached, important for cell signaling.
• Golgi complex – An organelle that modifies, sorts, and packages proteinsLarge molecules made of amino acids with various functions in the body. and lipidsOrganic molecules including fats, oils, and steroids. for transport.
• Interstitial fluid – The fluid surrounding cells within tissues.
• Intracellular fluid – The fluid inside a cell, primarily composed of cytosol.

L-N

• Lysosome – An organelle filled with digestive enzymesProteins that speed up chemical reactions in the body. that break down waste and cellular debris.
• Macrophage – A type of immune cell that engulfs and digests pathogens, debris, and dead cells.
• Microvilli – Tiny finger-like projections on some cells that increase surface area for absorption.
• Mitochondria – Organelles responsible for ATPThe energy currency of cells used for muscle contraction. production through cellular respirationThe process of gas exchange, including ventilation, external and internal respiration..

• Nucleus – The control centerThe part of a feedback loop that processes information and initiates a response. of the cell that contains DNA and directs cellular activities.
• Nuclear pore – Openings in the nuclear envelopeA double membrane that surrounds the nucleus and separates it from the cytoplasm. that allow substances to move between the nucleus and cytoplasm.
• Nuclear envelope – A double membrane that surrounds the nucleus and separates it from the cytoplasm.

P-R

• Peroxisome – An organelle involved in breaking down fatty acids and detoxifying harmful substances.
• Plasma membrane – The outer boundary of a cell that controlsVariables that remain constant to ensure a fair test. what enters and exits.
• Receptor protein – A membrane protein that binds to specific moleculesGroups of atoms bonded together. (ligands) and triggers a response.
• Ribosomes – Small structures responsible for protein synthesis, either free-floating or attached to the rough ER.
• Rough endoplasmic reticulum – A membrane network covered in ribosomesSmall structures responsible for protein synthesis, either free-floating or attached to the rough ER that produces and processes proteins.

S-V

• Smooth endoplasmic reticulum – A membrane network involved in lipid synthesis, detoxification, and calcium storage.
• Vesicle – A small, membrane-bound sac that transports substances within the cell.

• Antiport – A type of membrane transport in which two substances move in opposite directions across a membrane.
• Aquaporin – A membrane protein that forms waterThe universal solvent essential for life. channelsProtein passages in the cell membrane that allow specific molecules to pass through., allowing rapid water transport across cell membranes.
• Carrier protein – A membrane protein that binds to and transports substances across the cell membrane.
• Carrier-mediated transport – A form of membrane transport that relies on specific proteins to move substances.
• Cotransport – The simultaneous transport of two substances across a membrane by a single protein.
• Endocytosis – The process of a cell engulfing material by wrapping its membrane around it.
• Exocytosis – The process of expelling materials from a cell via vesicles that fuse with the plasma membraneThe outer boundary of a cell that controls what enters and exits..
• Facilitated diffusionPassive movement of molecules from areas of high to low concentration. – The passive transport of substances across a membrane using transport proteinsBind hormones for transport in the blood..

H-L

• Hydrostatic pressureThe force exerted by gases in the respiratory system, affecting airflow and gas exchange. – The pressure exerted by a fluid in a confined space, such as blood pressure.
• Hypertonic – A solutionA homogeneous mixture of two or more substances. with a higher solute concentration than the inside of a cell, causing water to leave the cell.
• Hypotonic – A solution with a lower solute concentration than the inside of a cell, causing water to enter the cell.
• Integral protein – A membrane protein embedded within the lipid bilayer, often spanning the entire membrane.
• Isotonic – A solution with the same solute concentration as the inside of a cell, maintaining equilibrium.
• Leak channel – A membrane protein channel that allows ionsCharged atoms or molecules. to move freely down their concentration gradientA difference in the concentration of a substance across a space..
• Ligand-gated channel – A membrane protein channel that opens or closes in response to a specific chemical signal.

M-Q

• Osmolarity – A measure of solute concentration in a solution.
• Osmosis – The movement of water across a selectively permeableA membrane that allows some substances to pass while blocking others. membrane from a lower solute concentration to a higher one.
• Osmotic pressure – The force exerted by water moving across a membrane due to osmosis.
• Peripheral protein – A protein located on the surface of the cell membrane, not embedded within it.
• Phagocytosis – A type of endocytosisThe process of a cell engulfing material by wrapping its membrane around it. in which a cell engulfs large particles or microorganisms.
• Pinocytosis – A type of endocytosis in which a cell takes in fluid and small dissolved substances.
• Primary active transport – Transport that requires ATP to move substances against their concentration gradient.

R-Z

• Receptor-mediated endocytosis – A selective form of endocytosis where receptors on the membrane help capture specific molecules.
• Secondary active transport – Transport that relies on an ion gradient created by primary active transport to move substances.
• Selectively permeable – A membrane that allows some substances to pass while blocking others.
• Simple diffusion – The passive movement of molecules across a membrane without the use of transport proteins.
• Sodium-potassium pump – A transport protein that moves sodium(Na⁺): Major ECF cation; important for fluid balance, nerve function. out of the cell and potassium(K⁺): Major ICF cation; essential for muscle and nerve function. into the cell using ATP.
• Symport – A type of cotransport in which two substances move in the same direction across a membrane.
• Tonicity – The ability of a solution to affect the water balance in a cell.
• Transmembrane protein – A protein that spans the entire cell membrane and is involved in transport or signaling.
• Uniport – A type of transport in which a single substance moves in one direction across a membrane.
• Voltage-gated channel – A membrane channel that opens or closes in response to changes in electrical charge.