Here is the correct labeling for the numbered boxes in "The Nitrogen Cycle" diagram, along with explanations for each step and the completed Key Points section.
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Labeled Boxes (1–7):
1. Nitrogen Fixation
→ This process converts atmospheric nitrogen gas (N₂) into usable forms like ammonia (NH₃). The arrow from “Nitrogen in the Air” to the plant’s roots (with bacteria in root nodules) indicates this step. Bacteria (like *Rhizobium*) in root nodules perform biological nitrogen fixation.
2. Nitrifying Bacteria
→ These bacteria convert ammonium ions (NH₄⁺) into nitrate ions (NO₃⁻), which plants can absorb. The box labeled “2” is positioned between “Ammonium ions” and “Nitrate ions,” showing this conversion step.
3. Uptake by roots
→ Plants absorb nitrate ions (NO₃⁻) through their roots to build amino acids and proteins. The arrow from “Nitrate ions” to the plant shows this uptake.
4. Feeding
→ Animals consume plants to obtain nitrogen-containing compounds (like proteins and amino acids). The arrow from the plant to the rabbit represents this transfer of nitrogen through the food chain.
5. Death and waste
→ When animals die or excrete waste, organic nitrogen is returned to the soil as decomposing matter. The arrow from the rabbit to the dead animal carcass illustrates this stage.
6. Decomposition
→ Decomposers (like bacteria and fungi) break down dead organisms and waste, releasing ammonium ions (NH₄⁺) back into the soil. The arrow from the dead animal to “Ammonium ions” represents decomposition.
7. Denitrifying Bacteria
→ These bacteria convert nitrates (NO₃⁻) back into nitrogen gas (N₂), which returns to the atmosphere. The arrow from “Nitrate ions” back to “Nitrogen in the Air” completes the cycle — this is denitrification.
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Key Points (Completed):
- A key type of organism involved in the cycling of nitrogen are
bacteria.
*(Bacteria drive nearly every step: fixation, nitrification, decomposition, denitrification.)*
- Nitrogen-
fixing bacteria are found in the root nodules of
legumes and can convert inert nitrogen gas into nitrogen-containing ions.
*(Legumes like beans and peas host symbiotic nitrogen-fixing bacteria.)*
- Nitrifying bacteria can convert ammonium ions to
nitrate ions, which can be taken up by the
roots of plants.
*(This is essential for making nitrogen available to most plants.)*
- Some bacteria, found in water-logged soils, convert nitrates back into nitrogen gas; these are known as
denitrifying bacteria.
*(They complete the cycle by returning N₂ to the atmosphere.)*
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✔ Final Answer Summary:
| Box # | Label |
|-------|------------------------|
| 1 | Nitrogen Fixation |
| 2 | Nitrifying Bacteria |
| 3 | Uptake by roots |
| 4 | Feeding |
| 5 | Death and waste |
| 6 | Decomposition |
| 7 | Denitrifying Bacteria |
Key Points Answers:
1. bacteria
2. fixing, legumes
3. nitrate, roots
4. denitrifying
This completes the diagram accurately according to the nitrogen cycle processes.
Parent Tip: Review the logic above to help your child master the concept of nitrogen cycle worksheet.
