Cells can make certain molecules when needed for a certain function. what happens when those molecules are no longer needed? they float freely in the cell. they return to the cell nucleus. they are broken down. they are stored for later use.

They are broken down.

Explanation:

Cell phones work in a highly regulated manner, quickly producing all the molecules necessary for their functioning in adequate quantities, avoiding the waste of energy and the accumulation of unnecessary molecules, at the moment.

Although rare, a cell can produce more molecules than necessary. Leaving these molecules free in the cellular environment can cause problems, for this reason, the cell digests these molecules, that is, the molecules are broken down.

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answer: substrate concentration. enzymes work best when there is a high enough substrate concentration for the reaction they catalyse.