AP BIO CH 7

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active transport

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37 Terms

1

active transport

The movement of a substance across a biological membrane against its concentration or electrochemical gradient with the help of energy input and specific transport proteins.

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2

amphipathic molecule

A molecule that has both a hydrophilic region and a hydrophobic region.

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3

aquaporin

A transport protein in the plasma membrane of a plant or animal cell that specifically facilitates the diffusion of water across the membrane (osmosis).

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4

concentration gradient

An increase or decrease in the density of a chemical substance in an area. Cells often maintain concentration gradients of ions across their membranes. When a gradient exists, the ions or other chemical substances involved tend to move from where they are more concentrated to where they are less concentrated.

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5

cotransport

The coupling of the downhilldiffusion of one substance to the uphilltransport of another against its own concentration gradient.

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6

diffusion

The spontaneous tendency of a substance to move down its concentration gradient from a more concentrated to a less concentrated area.

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7

electrochemical gradient

The diffusion gradient of an ion, representing a type of potential energy that accounts for both the concentration difference of the ion across a membrane and its tendency to move relative to the membrane potential.

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8

electrogenic pump

An ion transport protein that generates voltage across a membrane.

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9

endocytosis

The cellular uptake of macromolecules and particulate substances by localized regions of the plasma membrane that surround the substance and pinch off to form an intracellular vesicle.

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10

exocytosis

The cellular secretion of macromolecules by the fusion of vesicles with the plasma membrane.

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11

facilitated diffusion

The spontaneous passage of molecules and ions, bound to specific carrier proteins, across a biological membrane down their concentration gradients.

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12

flaccid

Limp. A walled cell is flaccid in surroundings where there is no tendency for water to enter.

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13

fluid mosaic model

The currently accepted model of cell membrane structure, which envisions the membrane as a mosaic of individually inserted protein molecules drifting laterally in a fluid bilayer of phospholipids.

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14

gated channel

A protein channel in a cell membrane that opens or closes in response to a particular stimulus.

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15

glycolipid

A lipid covalently attached to a carbohydrate.

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16

glycoprotein

A protein covalently attached to a carbohydrate.

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17

hypertonic

In comparing two solutions, referring to the one with a greater solute concentration.

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18

hypotonic

In comparing two solutions, referring to the one with a lower solute concentration.

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19

integral protein

Typically a transmembrane protein with hydrophobic regions that completely spans the hydrophobic interior of the membrane.

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20

ion channel

Protein channel in a cell membrane that allows passage of a specific ion down its concentration gradient.

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21

isotonic

Having the same solute concentration as another solution.

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22

ligand

A molecule that binds specifically to a receptor site of another molecule.

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23

membrane potential

The charge difference between a cell's cytoplasm and the extracellular fluid, due to the differential distribution of ions. Membrane potential affects the activity of excitable cells and the transmembrane movement of all charged substances.

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24

osmoregulation

The regulation of solute and water concentrations in body fluids by organisms living in hyperosmotic, hypoosmotic, and terrestrial environments.

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25

osmosis

The diffusion of water across a selectively permeable membrane.

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26

passive transport

The diffusion of a substance across a biological membrane.

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27

peripheral protein

A protein appendage loosely bound to the surface of a membrane and not embedded in the lipid bilayer.

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28

phagocytosis

A type of endocytosis involving large, particulate substances, accomplished mainly by macrophages, neutrophils, and dendritic cells.

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29

pinocytosis

A type of endocytosis in which the cell ingests extracellular fluid and its dissolved solutes.

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30

plasmolysis

A phenomenon in walled cells in which the cytoplasm shrivels and the plasma membrane pulls away from the cell wall when the cell loses water to a hypertonic environment.

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31

proton pump

An active transport mechanism in cell membranes that uses ATP to force hydrogen ions out of a cell, generating a membrane potential in the process.

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32

receptor-mediated endocytosis

The movement of specific molecules into a cell by the inward budding of membranous vesicles containing proteins with receptor sites specific to the molecules being taken in; enables a cell to acquire bulk quantities of specific substances.

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33

selective permeability

A property of biological membranes that allows some substances to cross more easily than others.

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34

sodium-potassium pump

A special transport protein in the plasma membrane of animal cells that transports sodium out of the cell and potassium into the cell against their concentration gradients.

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35

tonicity

The ability of a solution to cause a cell within it to gain or lose water.

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36

transport protein

A transmembrane protein that helps a certain substance or class of closely related substances to cross the membrane.

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37

turgid

Very firm. A walled cell become turgid if it has a greater solute concentration than its surroundings, resulting in entry of water.

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