หน้าที่ 16
Nitrogen Cycle
Nitrogen is important for the formation of amino acids in proteins Nitrogen is also needed to make chlorophyll in plants 79%o of the atmosphere is nitrogen gas However most organisms cannot use the nitrogen in this form it must be fixed in a usable form.
Lightning can fix nitrogen gas in the air into nitrate the nitrate enters the soil and is absorbed by plants to form plant proteins nitrogen can enter the soil some plants have special root nodules the bacteria in the root nodules fix the nitrogen into other compounds to be used by the plants.
Some bacteria in the soil fix the nitrogen in the soil to become other compounds such as ammonium nitrates plants absorb nitrates form the soil to make plant proteins when animals eat the plants the nitrogen is used to make animal proteins.
When the plants and animals dis the decomposers turn the nitrogen back into ammonium in the soil so that the nitrogen can re-enter the nitrogen cycle some bacteria in the soil return the extra nitrates back into nitrogen gas.