The nitrogen cycle

Nitrogen makes up about 78 percent of the atmosphere, but most organisms cannot use nitrogen gas directly, even though they need nitrogen to build proteins and DNA. In nitrogen fixation, bacteria in the soil and in the root nodules of plants like beans and peas convert nitrogen gas into ammonia, and other soil bacteria convert ammonia into nitrates that plants absorb through their roots. Animals get nitrogen by eating plants or other animals, decomposers return nitrogen from wastes and dead organisms to the soil as ammonia, and denitrifying bacteria turn nitrates back into nitrogen gas in the atmosphere. Human activity can disrupt this cycle: fertilizer runoff can overload lakes and coastal waters with nutrients, causing algal blooms whose decay uses up the oxygen in the water and kills fish.

This explanation is AI-generated and can occasionally be wrong. 🚩 Report