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SS2: BIOLOGY - 2ND TERM

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  1. Mechanism of the Respiratory System | Week 1
    6 Topics
    |
    2 Quizzes
  2. Mechanism of Gaseous Exchange in Plants | Week 2
    1 Topic
    |
    1 Quiz
  3. Excretory Systems I | Week 3
    5 Topics
    |
    1 Quiz
  4. Excretory Systems II | Week 4
    4 Topics
    |
    3 Quizzes
  5. Nutrient Cycling in Nature I | Week 5
    3 Topics
  6. Nutrient Cycling in Nature II | Week 6
    2 Topics
    |
    1 Quiz
  7. Ecological Management | Week 7
    4 Topics
  8. Ecological Tolerance | Week 8
    2 Topics
    |
    1 Quiz
  9. Adaptation | Week 9
    3 Topics
    |
    1 Quiz



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Topic Content:

  • Definition of Nitrogen Cycle
  • Ways by which Nitrogen is Added to the Soil in the Nitrogen Cycle
  • Ways by which Soil can Gain Nitrogen
  • Ways by which Soil Nitrogen is lost from the Soil
  • Importance of Nitrogen Cycle
  • Summary

A. What is the Nitrogen Cycle?

The nitrogen Cycle is a complex process through which nitrogen is converted into many forms, consecutively passing from the atmosphere, to the soil, to organisms and back into the atmosphere.

Nitrogen is naturally added and removed from the soil. It involves several processes such as nitrogen fixation, nitrification, denitrification, decay and putrefaction.

Ways by which Nitrogen is Added to the Soil in the Nitrogen Cycle:

  • Direct fixation by lightening during rainfall (Electrical discharge)
  • Nitrogen-fixing bacteria in the root nodules.
  • Ammonification.
  • Nitrification.
  • Decomposition of organic matter.
  • Application of nitrogenous fertilizers.
  • Incorporation into the soil by free-living bacteria or non-symbiotic bacteria.

1. Electrical Discharge:

Nitrogen can be fixed into the soil during lightening. A lightning bolt, because of its high temperature, can break the bonds of atmospheric nitrogen molecules.

Free nitrogen atoms in the air combine with oxygen in the air to create nitrogen oxides, which dissolve in rainwater to form mild acids (nitrous and nitric acids), that are carried to Earth’s surface by precipitation. These acids react with other compounds in the soil to form nitrates, very little nitrogen is fixed this way.

electrical discharge

2. Ammonification and Nitrification:

 

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