The answer is "Decomposers directly convert ammonium into nitrogen gas".
Living organisms such as plants and animals contains nitrogen in the form of the amino acids and proteins. When they die, the nitrogen in the form of ammonium is decomposed by microorganisms. It is then converted into nitrites and then to nitrates by nitrifying bacteria. The denitrifying bacteria then converts nitrates into nitrogen.
Energy cannot be created or destroyed; it can only change from one form to another. There is always as much energy after an event as there was before, but some of the energy may be wasted as heat that escapes into the surroundings.
Valves ensure blood flows toward your heart. Vein valves work to bring the blood that flowed down via arteries back up to your heart.
