Question

in order to function efficiently and to conserve energy and raw materials, a cell ______

never allows more than a few biochemical pathways to be active at any given time
maintains biochemical pathways active only when their products are needed
maintains all biochemical pathways active at all times

Explanation:

Cells regulate biochemical pathways to be energy - efficient. Activating all pathways all the time would be wasteful, and having only a few active at all times is not enough for diverse functions. Cells activate pathways when their products are required.

Answer:

B. maintains biochemical pathways active only when their products are needed