nitrogen cycle

• nitrogen in the air gets turned into nitrates by nitrogen-fixing bacteria

  nitrates are then absorbed by plants to make amino acids

  amino acids then pass into animals that eat the plants

  animals release waste products such as urea

  both plants and animals die

  so we get nitrogen in waste products and dead remains
• decomposing bacteria now convert the nitrogen into ammoniafinally nitrifying bacteria convert the ammonia into nitratesnitrates can now be absorbed again by plants and cycle repeatsbacteria in the soil break down nitrates back into nitrogen gas which returns to the air called denitrifying bacteria
• 1. Both plants and animals need nitrogen in order to survive, but neither plants or animals can absorb the nitrogen in the air (atmospheric nitrogen). Animals get their nitrogen from digesting plants (or other animals), and plants must get their nitrogen from the soil, either as nitrates or ammonium ions (two chemicals that contain nitrogen)
• 2.The processes of nitrogen fixation and then nitrification cover how atmospheric nitrogen gets converted to nitrates. This happens either in a single step (via lightning), or via a multi-step process (nitrogen fixation and then nitrification) carried out by nitrogen-fixing bacteria, and then nitrifying bacteria.
• 3.Separately to the above, decomposers break down plant and animal waste to produce ammonia. This ammonia then reacts to form ammonium ions (which plants can absorb)
• 4.Plants absorb nitrates and ammonium ions from the soil, and use them to create essential biological molecules such as proteins and DNA. This process is called assimilation, and is how nitrogen becomes part of the plant's tissues, and enters the food chain
• 5.At the same time as all of the above, some of the nitrates in the soil are being converted back into atmospheric nitrogen due to the process of denitrification (due to denitrifying bacteria).