What are the structures that allow for one-way blood flow through the heart
1) atria
2) ventricles
3) valves
4) capillaries

The answer is valves.

Heart valves have a particularly important role in keeping blood flow in a certain direction, allowing blood to flow from the atria to the ventricles and from the ventricles to the heart. Valves control the flow of blood through the heart by opening and closing each time the heart contracts. The valve's opening and closing functions are controlled by the pressure difference between the heart chambers and some muscles in the heart.

In case of dysfunction of one of these valves can be made an artificial heart valve or a mechanical type

there are so many examples for that in different areas, like biology experiment carried out in our lab recently.

here's one link:

step 1: nitrogen fixation- conversion of atmospheric no₂ into forms useful to plants by lightning, bacteria, and cyanobacteria.

step 2: nitrification-process of converting ammonia to nitrite or nitrate.

step 3: assimilation-plant roots absorb new form of nitrogen.

step 4: ammonification-conversion of organic nitrogen to ammonia by bacteria involved in decomposition.

step 5: denitrification-bacteria turns the decomposed matter back into n₂o, which is released into atmosphere; repeat cycle.