Here's a breakdown of why:

* Proteins: Enzymes are almost always proteins, complex molecules made up of amino acids.

* Speed up chemical reactions: This is the primary function of enzymes. They act as catalysts, lowering the activation energy required for a reaction to occur, thus making the reaction proceed much faster.

* Without requiring high temperatures: Enzymes allow reactions to happen quickly at the normal temperatures found within cells. Without enzymes, many essential reactions would occur too slowly to sustain life.

In summary: Enzymes are proteins that act as biological catalysts, speeding up chemical reactions in cells without the need for extreme temperatures.