Final answer:
Yeast is the leavening agent that is a living microorganism and is used in baking to make dough rise.
Step-by-step explanation:
The leavening agent that is a living microorganism is Yeast. Yeast is a type of fungi that is used in baking to make dough rise. It ferments the sugars in the dough, producing carbon dioxide gas which gets trapped in the gluten network, causing the dough to expand and become light and fluffy.
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