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active transport

the movement of materials through a cell membrane using energy


(adenosine triphosphate) main energy source that cells use for most of their work


(biology) the basic structural and functional unit of all organisms

cell theory

idea that all living things are composed of cells, cells are the basic units of structure and function in living things, and new cells are produced from existing cells

cell wall

strong layer around the cell membrane in plants, algae, and some bacteria


an organelle found in plant and algae cells where photosynthesis occurs


short, hair-like structures made of microtubules that enable movement of cells or movement of materials outside a cell


describes how much solute is present in a solution compared to the amount of solvent


study of cells


process by which molecules tend to move from an area where they are more concentrated to an area where they are less concentrated


process by which a cell takes in a substance by surrounding it with the cell membrane

endoplasmic reticulum

a system of membranes that is found in a cell's cytoplasm and that assists in the production, processing, and transport of proteins and in the production of lipids


When the concentration of a solute is the same throughout a solution

eukaryotic cell

A type of cell with a membrane-enclosed nucleus and membrane-enclosed organelles. Examples of organisms with these cells are protists, plants, fungi, and animals.


the process by which a substance is released from the cell through a vesicle that transports the substance to the cell surface and then fuses with the membrane to let the substance out

facilitated diffusion

movement of specific molecules across cell membranes through carrier proteins


long, thin, whip-like structures, with a core of microtubules, that enable some cells to move

golgi apparatus

stack of membranes in the cell that modifies, sorts, and packages proteins from the endoplasmic reticulum


describes a solution whose solute concentration is higher than the solute concentration inside a cell; net water flow is going out of a cell


when comparing two solutions, the solution with the lesser concentration of solutes; net water flow is going into a cell


having a solute concentration equal to that of another solution; net water flow is in equilibrium


membrane-bound sac(organelle) containing digestive enzymes that can break down proteins, nucleic acids, and polysaccharides


thin layer that separates various cellular structures or organs


solid rod of protein, thinner than a microtubule, that enables a cell to move or change shape; found in eukaryotic cells


straight, hollow tube of proteins that gives rigidity, shape, and organization to a cell


Powerhouse of the cell, organelle that is the site of ATP (energy) production

nuclear envelope

layer of two membranes that surrounds the nucleus of a cell


The organelle where ribosomes are made, synthesized and partially assembled, located in the nucleus


specialized structure that performs important cellular functions within a eukaryotic cell (prokaryotic cells have some)


diffusion of molecules through a semipermeable membrane from a place of higher concentration to a place of lower concentration until the concentration on both sides is equal

passive transport

transport of a substance across a cell membrane by diffusion

permeable membrane

a membrane that allows for diffusion of certain solutes and water

phospholipid bilayer

two-layer "sandwich" of molecules that surrounds a cell

plasma membrane

thin flexible barrier that regulates what enters and exits the cell; composed of two layers of lipids

prokaryotic cell

A type of cell lacking a membrane-enclosed nucleus and membrane-enclosed organelles; found only in the domains Bacteria and Archaea.


small organelle in the cell on which proteins are assembled; made of RNA and protein

selectively permeable

a property of cell membranes that allows some substances to pass through, while others cannot


cell organelle that stores materials such as water, salts, proteins, and carbohydrates


small membrane-bound sac that functions in moving products into, out of, and within a cell

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