Question

which class of molecules is responsible for speeding up chemical reactions

Answer 1

catalysts

Answer 2

enzymes

Answer 3

Enzymes. :)

Answer 4

Enzymes are a type of Catalyst.

Answer 5

if you're talking about homogeneous and heterogeneous catalysts, although the latter can speed up chemical reaction, it changes the state of equilibrium and is inorganic. And since this is a biology question, I suppose enzyme as an answer is more fitting.

Answer 6

but you should be credited for pointing out a fact.