The Nitrogen Cycle worksheet showing the process of nitrogen transformation in the environment.

Here’s the completed worksheet based on the Nitrogen Cycle diagram and standard scientific knowledge:

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The Nitrogen Cycle

1. Label the steps of the nitrogen cycle using the diagram above:

*(Based on typical nitrogen cycle diagrams and the arrows shown in your image — assuming standard labeling)*

1. Nitrogen fixation (by bacteria or lightning) – Atmospheric N₂ is converted to usable forms (like ammonia) by bacteria in soil/roots or via lightning.
2. Nitrification – Ammonia (NH₃) is converted to nitrites (NO₂⁻), then to nitrates (NO₃⁻) by soil bacteria.
3. Assimilation – Plants absorb nitrates from the soil and use them to build proteins and DNA.
4. Consumption / Food chain transfer – Animals eat plants (or other animals) and obtain nitrogen-containing compounds.
5. Decomposition / Ammonification – When organisms die, decomposers (bacteria/fungi) break down organic matter and release ammonia back into the soil.
6. Denitrification – Bacteria convert nitrates back into nitrogen gas (N₂), which returns to the atmosphere.

> *Note: The exact numbering may vary slightly depending on how arrows are drawn in your diagram, but these 6 steps represent the core processes.*

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2. Roughly ___ percent of the atmosphere is composed of nitrogen gas.

✔ 78%

*(Nitrogen gas (N₂) makes up about 78% of Earth’s atmosphere by volume.)*

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3. Which organisms act as a bridge between the nitrogen in the atmosphere and the nitrogen on land?

✔ Nitrogen-fixing bacteria (e.g., *Rhizobium* in legume root nodules, free-living soil bacteria like *Azotobacter*, or cyanobacteria)

*(These bacteria convert atmospheric N₂ into ammonia (NH₃), making nitrogen available to plants and entering the terrestrial food web.)*

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4. Since humans need nitrogen but cannot get it from the air, we instead get nitrogen from ___

✔ eating plants and/or animals (or “the food we eat”)

*(Humans obtain nitrogen by consuming proteins from plant-based or animal-based foods — since we can’t directly use atmospheric N₂.)*

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5. Lightning combines nitrogen and oxygen in the air to form ___

✔ nitrogen oxides (like NO or NO₂) → which eventually become nitrates (NO₃⁻) in rainwater that fertilize soil.

*(Lightning provides enough energy to break the strong triple bond in N₂ and allow it to react with O₂, forming nitrogen oxides. These dissolve in rain to form nitric acid, which becomes usable nitrate for plants.)*

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✔ Final Answers Summary:

1.
1. Nitrogen Fixation
2. Nitrification
3. Assimilation
4. Consumption
5. Decomposition/Ammonification
6. Denitrification

2. 78%

3. Nitrogen-fixing bacteria

4. eating plants and/or animals (or “food”)

5. nitrogen oxides (or nitrates — depending on level; both acceptable, but “nitrogen oxides” is more precise for what lightning directly forms)

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Let me know if you’d like this formatted as a printable answer sheet! 🌱⚡