Billion Oyster Project

Nitrogen Transformations in Your Tank


Nitrogen Cycle Investigation



Class Periods




Subject Areas



Students compare and contrast multiple diagrams that describe nitrogen transformations in tanks.  They evaluate the pros and cons of different diagrams, and use them to uncover information about how nitrogen enters a tank, gets transformed by the organisms in the tank, and ultimately leaves the tank.  Students consider whether there is a complete ‘cycle’ of nitrogen within a tank.


  • Identify similarities and differences between multiple diagrams on the same topic.

  • Identify strengths and weaknesses of multiple diagrams on the same topic.

  • Evaluate whether a complete nitrogen cycle is likely to occur in the classroom tank.

Materials and Resources

Teacher Resources


Molecular models of ammonia/ammonium, nitrite, nitrate, nitrogen gas -- one set for each group.  Note: students build their own models in the previous lesson, Get to Know a Few Nitrogen Molecules.

Instruction Plan


  1. Students get their molecular models of ammonia/ammonium, nitrite, nitrate, and nitrogen gas, since they will need them later.
  2. Revisit the powerpoint Tilapia in Tanks.
  3. Ask students to brainstorm: “If a nitrite spike can kill all those animals, what are some different ideas about how it’s possible to keep a lot of animals, alive and healthy, in a tank?”
  4. And: “What questions do you have now about about how it’s possible to keep a lot of animals, alive and healthy, in a tank?”


  1. In small groups, students examine Diagrams that Describe Nitrogen Changes in Tanks  

  2. They go through each diagram and place their models of ammonia/ammonium, nitrite, nitrate, and/or nitrogen gas on the diagram in the appropriate location.

  3. Students identify the sequence of nitrogen transformations in a tank:

    • First is (ammonia/ammonium)

    • Then that gets transformed into (nitrites)

    • Finally, that gets transformed into (nitrates)


  1. In pairs, students choose two sources’ diagrams to study in depth, and complete Compare and Contrast Diagrams that Describe How to Regulate Nitrogen in Your Tank.

  2. Ask fast-working pairs to create their own version of these diagrams, which should be, in their opinion, an improvement on all of the ones that they studied.


Students debrief in a full-class discussion.  

  • Insist that students refer to specific elements from specific diagrams.  

  • Insist that the rest of the class turn to those diagrams and examine those elements afresh.  

  • Ask the group if they understand those elements to mean exactly the same thing.  Often they don’t, and in those cases, ask everyone to search for other evidence within the diagram to support or contradict one of the interpretations that a student has suggested.

  • Post of points of disagreement, shared understandings, and persistent questions.


NGSS - Cross-Cutting Concepts

  • Energy and Matter

    • Matter is conserved because atoms are conserved in physical and chemical processes.

NGSS - Disciplinary Core Ideas

  • ESS2.A: Earth’s Materials and Systems

    • All Earth processes are the result of energy flowing and matter cycling within and among the planet’s systems. This energy is derived from the sun and Earth’s hot interior. The energy that flows and matter that cycles produce chemical and physical changes in Earth’s materials and living organisms.
  • LS2.B: Cycle of Matter and Energy Transfer in Ecosystems

    • Food webs are models that demonstrate how matter and energy is transferred between producers, consumers, and decomposers as the three groups interact within an ecosystem. Transfers of matter into and out of the physical environment occur at every level. Decomposers recycle nutrients from dead plant or animal matter back to the soil in terrestrial environments or to the water in aquatic environments. The atoms that make up the organisms in an ecosystem are cycled repeatedly between the living and nonliving parts of the ecosystem.

NYC Science Scope & Sequence - Units

  • Grade 6, Unit 4

    • Interdependence

NYS Science Standards - Major Understandings

    • Matter is transferred from one organism to another and between organisms and their physical environment. Water, nitrogen, carbon dioxide, and oxygen are examples of substances cycled between the living and nonliving environment.