Answer:
Cell
Explanation:
I'm not 100% what you mean by "building block", but because your subject is biology, I will assume that you mean a cell.
In general, a cell is considered the "building block" of life because everything that is alive is made up of cells.
Hope I helped :)
<span>a large landmass that is part of a continent
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Zippy Xylem. The xylem of a plant is the system of tubes and transport cells that circulates water and dissolved minerals.