Substances that promote chemical reactions in living things but are not affected by the reaction are called enzymes.

Here's why:

* Catalysts: Enzymes act as catalysts, which means they speed up chemical reactions without being consumed in the process.

* Specificity: Enzymes are highly specific, meaning they only catalyze certain reactions involving specific molecules called substrates.

* Unchanged: After a reaction, enzymes remain unchanged and can be used again to catalyze the same reaction.

Let me know if you have any other questions!