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Leaving certificate biology

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  1. Ecology theory
    5 Topics
    |
    1 Quiz
  2. Unit 1
    Nutrient recycling
    4 Topics
    |
    1 Quiz
  3. Ecological relationships and population dynamics
    2 Topics
  4. Human impact on the ecosystem
    2 Topics
  5. Study of a grassland ecosystem
    3 Topics
  6. Responses in the Flowering Plant
    4 Topics
    |
    1 Quiz
  7. Unit 3
    Sexual reproduction in the flowering plant
    1 Topic
  8. The human reproductive system
    3 Topics
  9. The menstrual cycle
    2 Topics
  10. Pregnancy
    2 Topics
  11. The circulatory system
    4 Topics
  12. Blood
    5 Topics
  13. The heart
    5 Topics
Lesson 2, Topic 3
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The nitrogen cycle

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What is the nitrogen cycle ?

  • The nitrogen cycle is the biogeochemical cycle by which nitrogen is converted into multiple chemical forms as it circulates among atmosphere, terrestrial, and marine ecosystems. The conversion of nitrogen can be carried out through both biological and physical processes

Why is the nitrogen cycle important ?

  • Plants need nitrogen to make protein.
  • Plants can not use the nitrogen gas in the air to do this
  • The nitrogen cycle allows plants via bacteria to get nitrogen in a form they can use to make proteins

The role of nitrogen fixing bacteria in the nitrogen cycle

  • They are found in swellings called nodules on the roots of legumes (peas , beans).
  • These bacteria convert nitrogen gas into nitrate
  • Plants can then use these nitrates to make protein
  • This is an example of mutualism as both organisms benefit

The role of decomposers in the nitrogen cycle

  • When animals eat plants they assimilate the nitrogen in the plants into their own proteins
  • When plants and animals die they are decomposed by bacteria and fungi in the soil
  • As they decay nitrogen compounds such as ammonium salts are released into the soil

The role of nitrifying bacteria in the nitrogen cycle

  • Nitrifying bacteria in the soil convert ammonium salts into nitrites and then onto nitrates
  • These nitrates ate absorbed by plants to make proteinĀ 

The role of denitrifying bacteria in the nitrogen cycle

  • They convert nitrates into nitrogen gas

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