8.8 - Nitrogen cycle

• What is nitrogen fixation?

  It is the process by which atmospheric nitrogen in the air is converted to nitrates and ammonia in the soil.
• Describe the 2 ways in which nitrogen fixation takes place.

  - Via lightning - lightning converts atmospheric nitrogen directly into nitrates.

  - Via nitrogen-fixing bacteria - these convert atmospheric nitrogen into ammonia. Nitrogen-fixing bacteria are found in the soil, and also in the roots of some plants.
• What carries out nitrification?

  nitrifying bacteria in the soil
• What are the 2 steps to nitrification?

  - Ammonia in the soil is first converted to nitrites.

  - Those nitrites are then converted to nitrates.
• How does nitrogen enter the food chain?

  - assimilation - when animals eat plants they assimilate these nitrogen containing compounds (e.g. proteins) into their own bodies.
• What is assimilation?


  It is the process by which plants absorb nitrates and ammonium ions, and use them to create biological molecules such as proteins.
• Decomposition occurs when ...

  ... decomposers feed on the waste excretions of animals, and the rotting corpses of dead plants and animals. During this process they convert urea and proteins into ammonia.
• Why is decomposition important?

  - It is important because the ammonia in the soil forms ammonium ions, which is one of few the nitrogen-containing compounds plants can absorb and assimilate.

  - NOTE: that the some of the ammonia produced by nitrogen fixation is also converted to ammonium ions.
• What is denitrification?


  It's when denitrifying bacteria in the soil convert nitrates back into atmospheric nitrogen.
• Why is denitrification bad for plants?

  It means there are fewer nitrates in the soil, reducing the amount available for the plants to absorb and assimilate.
• Name 2 biological molecules contain nitrogen.


  Proteins, DNA
• What is the name of the process that converts ammonia to nitrite, and then to nitrates?

  Nitrification
• What is the name of the process that converts nitrates to atmospheric nitrogen?

  Denitrification
• Which process describes how plants use nitrogen to build biological molecules, that the plants then incorporate into their bodies?

  Assimilation
• True or false? Plants can absorb atmospheric nitrogen.

  FALSE - Nitrogen must be in the form of ammonium ions or nitrates for plants to be able to absorb it.
• What are the microorganisms responsible for converting atmospheric nitrogen to ammonia/ammonium ions called?

  Nitrogen-fixing bacteria
• True or false? Nitrogen-fixing bacteria are found in lightning.

  FALSE - Lightning converts atmospheric nitrogen directly into nitrates.