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43 Cards in this Set
- Front
- Back
the smallest unit of life
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cell
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the gatekeeper of the cell, which allows only specific substances in or out and passes chemical messages from the external environment to the cell's interiror
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plasma membrane
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- selectively isolates the cell's contents from the external environment
- regulates the exchange of essential substances between the cell's contents and the external environment - communicates with other cells |
functions of the plasma membrane
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model of the plasma membrane
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fluid mosaic model
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consists of all of a cell's internal contents, including all the organelles except the nucleus, in eukaryotes; mostly water
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cytoplasm
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double layer within the plasma membrane which phospholipids spontaneously arrange themselves into
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phospholipid bilayer
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membrane proteins and their attached carbohydrates
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glycoproteins
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regulates the movement of hydrophilic molecules through the plasma membrane
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transport proteins
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forms pores or channels that allow small water-soluble molecules to pass through the membrane
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channel proteins
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binding sites that can temporarily attach to specific molecules on one side of the membrane to change the protein's shape and move the molecule across the membrane
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carrier proteins
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trigger cellular responses when specific molecules in the extracellular fluid bind to them
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receptor proteins
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serve as identification tags and cell-surface attachment sites
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recognition proteins
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any substance that can move or change shape in response to external forces without breaking apart
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fluids
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the number of molecules in a given unit of volume
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concentration
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a physical difference in properties such as temperature, pressure, electrical charge, or concentration of a particular substance between two adjoining regions
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gradient
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a difference in concentration of those substances between one region and another
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concentration gradient
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the net movement of molecules from regions of high concentration to regions of low concentration
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diffusion
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occurs when no factors, such as electrical charge, pressure differences, or physical barriers, are opposing the movement of diffusion; the moevement of molecules from regions of high to low concentration will continue until the substance is evenly dispersed through the fluid or the air
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dynamic equilibrium
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movement of substances across a membrane, going down a gradient of concentration, pressure, or electrical charge. does not require the cell to expend energy
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passive transport
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diffusion of water, dissolved gasses, or lipid-soluble molecules through the phospholipid bilayer of a membrane
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simple diffusion
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diffusion of usually water-soluble molecules through a channel or carrier protein
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facilitated diffusion
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diffusion of water across a selectively permeable membrane - that is, a membrane that is more permeable to water than to dissolved molecules
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osmosis
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movement of substances into or out of a cell using cellular energy
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energy-requiring transport
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movement of individual small molecules or ions through membrane-spanning proteins, using cellular energy, usually ATP
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active transport
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movement of large particles, including large molecules or entire microorganisms, into a cell by engulfing extracellular material, as the plasma membrane forms membrane-bound sacs that enter the cytoplam
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endocytosis
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movement of materials out of a cell by enclosing the material in a membranous sac that moves to the cell surface, fuses with the plasma membrane, and opens to the outside, allowing its contents to diffuse away
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exocytosis
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property of the membrane that allows some molecules to pass through, or *permeate*
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selectively permeable
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a barrier that prevents the passage of all molecules
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impermeable
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(during osmosis) the equal movement of water into and out of cells
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isotonic
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(during osmosis) the net water movement out of cells
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hypertonic
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(during osmosis) the net water movement into cells
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hypotonic
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a membranous sac
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vesicle
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(type of endocytosis) a dimple forms in the plasma membrane, which deepens and surrounds the extracellular fluid; the membrane encloses the fluid, forming a vesicle
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pinocytosis
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(type of endocytosis) the plasma membrane extends pseudopods toward an extracellular particle (for example, food); the ends of the pseudopods fuse, encircling the particle; a vesicle called a food vacuole is formed containing the engulfed particle
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phagocytosis
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(type of endocytosis) receptor proteins for specific molecules or complexes of molecules are localized at coated pit sites; the receptors bind the molecules and the membrane dimples inward; the coated pit region of the membrane encloses the receptor-bound molecules; a vesicle containing the bound molecules is released into the cytoplasm
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receptor-mediated endocytosis
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junction made of protein strands that holds cells together
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desmosomes
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junction formed by strands of protein that seal cells together by wrapping around them and making them leak-proof
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tight junctions
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junction made of pairs of channels that connect the insides of adjacent cells and allows cells to communicate by allowing the flow of certain substances from cell to cell; found in animal cells
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gap junctions
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juction that connects the inside of adjacent cells and allows communication and the transfer of certain materials between cells; found in plant cells
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plasmodesmata
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the outer surfaces of the cells of bacteria, plants, fungi, and some protists
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cell wall
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the part of the cell wall that is formed by cellulose
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primary cell wall
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the part of the cell wall that is formed by lignin
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secondary cell wall
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carbohydrate attached to the head of a phospholipid
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glycolipid
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