He lock-and-key mechanism refers to the complementary shapes of an enzyme and a substrate. the attractive forces between an enzyme and a substrate. the ability of an enzyme to lower the activation energy of a reaction. the ability of an enzyme to "unlock" the products of a reaction.

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to figure the total magnification of an image that you are viewing through the microscope is really quite simple. to get the total magnification take the power of the objective (4x, 10x, 40x) and multiply by the power of the eyepiece, (usually 10x)

answerwestern plateau,     central lowlands,     great dividing range;

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