4. Nitrogen Fixation Plants need nitrogen in order to grow, but they cannot use the N 2 in the atmosphere - It must be FIXED first

5. Bacteria do this Fixation Bacteria in the soil and water convert N 2 to NH 4 + (ammonia) = NITROGEN FIXATION

6. This fixed nitrogen can be used by plants to make DNA and Proteins We get our nitrogen by eating plants. We use this nitrogen to make our DNA and proteins

7. When bacteria detect there is too much nitrogen in the soil, they denitrify it = DENITRIFICATION DENITRIFICATION turns nitrogen back into a gas

8. Back to the soil When plants and animals die, they DECOMPOSE and are broken down by DECOMPOSERS (bacteria and fungi) DECOMPOSERS add nitrogen to the soil