Enzymes influence chemical reactions in living systems by

Often, reactants are found in low concentrations. Because the reactions must take place very quickly, they usually need a catalyst. Enzymes are catalysts for chemical reactions in living things. Enzymes, like other catalysts, lower the activation energy and increase the rate of chemical reac- tions.

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(im only a 6th grader so I might be wrong but this is how i define it)

answer: the blood-brain barrier is a layer of specialized membranes and cell processes designed to keep undesirable substances from passing from the bloodstream into the precious tissues of the brain. while the blood-brain barrier does keep most bad things out of the central nervous system, it is not impermeable.

explanation:

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