Yeast breaking down starch into usable energy law of thermodynamics.

Yeast breaking down starch into usable energy obeys the first law of thermodynamics.

Explanation:

The first law of thermodynamics expresses the conservation of energy, specifically states that the internal energy of a system equals the difference of the heat transfer and the work done by the system.

But, the conservation of energy part is what applies here directly, because the yeast breakes down starch into fat, which is another form of energy, there's the conservation. Then, when this fat breaks down, it's to release the last form of energy of that process, the energy that will be used and transform in heat, there's presents the first law of thermodynamics, because such energy released will be able to be used as work.