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| 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, substances tend to move from where they are more concentrated to where they are less concentrated. |
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| The spontaneous tendency of a substance to move down its concentration gradient from where it is more concentrated to where it is less concentrated. |
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| The diffusion of water across a selectively permeable membrane. |
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| A solution having the same solute concentration as another solution, thus having no effect on passage of water in or out of the cell. |
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| In comparing two solutions, the one with the greater concentration of solutes; cells in such a solution will lose water to their surroundings. |
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| In comparing two solutions, the one with the lower concentration of solutes; cells in such a solution will take up water from their surroundings. |
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| The movement of a substance across a biological membrane against its concentration gradient, aided by specific transport proteins and requiring input of energy (often as ATP). |
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| A chemical bond resulting from the attraction between oppositely charged ions. |
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| An attraction between atoms that share one or more pairs of outer-shell electrons; symbolized by a single line between the atoms. |
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| An atom that has gained or lost one or more electrons, thus acquiring a charge. |
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| The dissolving agent of a solution. Water is the most versatile solvent known. |
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| A substance that is dissolved in a solution. |
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| A measure of the relative acidity of a solution, ranging in value from 0 (most acidic) to 14 (most basic). The letters pH stand for potential hydrogen and refer to the concentration of hydrogen ions (H). |
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| A substance that increases the hydrogen ion concentration in a solution. |
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| A substance that decreases the hydrogen ion (H) concentration in a solution. |
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| An assemblage of atoms commonly attached to the carbon skeletons of organic molecules and usually involved in chemical reactions. |
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| A chemical process in which two molecules become covalently bonded to each other with the removal of a water molecule. Also called condensation. |
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| A chemical process in which polymers are broken down by the chemical addition of water molecules to the bonds linking their monomers; an essential part of digestion. |
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| Member of the class of biological molecules consisting of simple single-monomer sugars (monosaccharides), two-monomer sugars (disaccharides), and other multiunit sugars (polysaccharides). |
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| An organic compound consisting mainly of carbon and hydrogen atoms linked by nonpolar convalent bonds, making the compound mostly hydrophobic. Lipids include fats, phospholipids, and steroids and are insoluble in water. |
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| A polymer consisting of many nucleotide monomers; serves as a blueprint for proteins and, through the actions of proteins, for all cellular structures and activities. The two types of nucleic acids are DNA and RNA |
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| A functional biological molecule consisting of one or more polypeptides folded into a specific three-dimensional structure. |
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