Teacher Guide: Nitrogen Cycle STEM Case and Handbook
Grade Level: 9th - 12th
Subjects: Biology, AP Biology
Versions: Biology and AP Biology
Time: Biology 40-50 mins; AP Biology 60-80 mins
STEM Role: EPA Environmental Engineer
Preview Video: Nitrogen Cycle Preview Video
Introduction: An infant on a farm has blue
baby syndrome. As an EPA environmental
engineer, students must find the cause of
the baby’s illness. Using data from the
environment, students learn the importance
of the nitrogen cycle and how human
factors can impact nature.
Learning Objectives: STEM Cases are designed to help students learn the core concepts and
practice critical thinking skills (data analysis, data interpretation, hypothesis and reasoning,
predictions and communicating findings). Students are assessed on each of these and their
progress can be monitored in real time by teachers. The following concepts are addressed in the
Nitrogen Cycle STEM Case:
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Importance of nitrogen (DNA, proteins,
amino acids), sources of nitrogen
●
Nitrogen cycle, nitrogen gas, ammonia,
nitrites, nitrates, enzymes, bacteria of the
nitrogen cycle, nitrogen fixation, nitrification,
denitrification, ammonification, assimilation,
decomposition
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Humans impacts on the nitrogen cycle,
fertilizers, wastewater treatment, bloom
zones
●
Plant anatomy on
chloroplasts and roots
●
Biology Expanded Handbook Only: Amino acid structure, ammonia dissolving in water
(ammonia vs. ammonium), ATP in nitrogenase synthesis of ammonia
●
AP Version Only: Reduction, oxidation, redox reactions
leaves,
stomata,
Vocabulary: Every STEM Case and Handbook contains a glossary containing all of the
vocabulary needed for the activity. As new vocabulary is introduced, the words are presented as
orange text - clicking the orange text opens the glossary page for that term. The glossary can
also be opened at any time throughout the case.
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Lesson Summary: At the start of the Nitrogen Cycle
case study students are sent a report from a hospital
about a baby named Jennifer who has blue baby
syndrome. The report shows a timeline of the baby’s
symptoms as well as 4 other blue baby cases in the
area. While Jennifer has recovered, it is vital that the
cause of the blue baby syndrome cases is found to
prevent further cases. Since blue baby syndrome
can be caused by high nitrates in drinking water, the
students must examine the local water nitrate levels.
Before they can start their investigation, students
enter the Nitrogen Cycle Handbook to the learn the
science needed to solve the problem. The Handbook is an interactive guide that introduces
students to each step in the nitrogen cycle. The students learn about the nitrogen cycle by building
it step-by-step and learn how human activities that impact the cycle can have important
consequences.
Once the Handbook is complete students travel to Jennifer’s home to collect water samples. They
collect data on the ammonia, nitrite, and nitrate levels in the well water and at various locations in
the river between her home and a nearby town. Analyzing and interpreting this data leads the
students to identify the town’s wastewater treatment plant as the source of the problem. Inside
the treatment plant, students are introduced to a 3-stage water treatment system. The tanks at
the plant are not in the correct order and, using their learning from the Handbook about the
nitrogen cycle, the students must put the tanks in the correct order to fix the problem.
Students then recollect the data and realize that the problem has not been entirely solved. This
leads them to collect more data further upriver and discover other sources of nitrates from human
activities. At the conclusion of the Nitrogen Cycle case, students write a case summary to
communicate their findings and practice scientific writing skills.
Recommended STEM Case Order: The
Nitrogen Cycle STEM Case should not be used
as the first case experience for your students as
the nitrogen cycle is a difficult process for many
students to learn. We highly recommend that
students use one of the introductory case
studies first such as diffusion, osmosis, or
homeostasis to help familiarize students with
the case study format. Using the Enzymes case
prior to using the case will also help your
students.
Follow Up: Your students can learn more about
the nitrogen cycle and human impacts here:
●
●
●
Nitrate in the Mississippi River Basin
Nitrates in Drinking Water
Science Careers at the EPA
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Scientific Background: Nitrogen is the most
abundant gas in earth’s atmosphere and is a
vital component of many molecules in plants and
animals. The cycling of nitrogen within an
environment is vital in both terrestrial and marine
ecosystems and human activities can negatively
impact this cycle. One example is the
occurrence of increased levels of nitrates in
drinking water.
In humans, the enzymes required to metabolize
nitrates are not synthesized until the individual is
6 months old. As such, nitrates can be toxic to
infants under this age resulting in blue baby
syndrome which is associated with a blueness of
the skin (particularly around the mouth and extremities. Nitrates from polluted water enter the
infant’s red blood cells and transforms the protein hemoglobin to methemoglobin. Increases in
methemoglobin in the blood (methemoglobinemia) reduces the delivery of oxygen to the tissues
of the body. Blood with high levels of methemoglobin has a chocolatey brown color rather than
the usual red color of normal blood.
Hemoglobin has 4 subunits, each of which can bind an oxygen molecule in areas of high oxygen
concentration (the lungs and arteries) and release the oxygen in areas of low oxygen
concentration (the capillaries in organs and tissues. Each subunit contains the ferrous form of the
iron ion (Fe2+) that binds the oxygen molecule. Nitrates transform the ion to the ferric form (Fe3+),
which has two effects. First, the affected subunit has a decreased affinity for oxygen, which
decreases the oxygen carrying capacity of the protein. However, the second effect is to increase
the affinity of the other 3 subunits for oxygen. This increased affinity means that the other subunits
hold on the oxygen very tightly and prevents the release of oxygen into organs and tissues.
Severe cases of methemoglobinemia can result in seizures, coma and death.
Teacher Preview Version: We highly recommend teachers complete the teacher version of a
case study before assigning a case to their class. In the teacher version, the pages are “unlocked”
which means that you are able to move from page to page without answering questions. You can
use this version to familiarize yourself with the activities that students will complete. You can also
use it to review concepts with your class by presenting it via a projector or smartboard.
Handbook: The Expanded Handbook that
accompanies the Biology version of this case
has extra sections on ammonia vs ammonium, in
addition to the concepts covered in the handbook
section of the High School Case. The AP
Handbook is the same as the Handbook in the
AP version of the case. It can be used as an
introduction to the concepts prior to taking the
case, as a review of concepts before exams, as
homework, extra credit or as part of a flipped
classroom approach (students could complete
the Handbook at home and then complete the
case in-class). If class time is limited, the
handbook could also be used as a replacement
for the case as it only takes 15-20 minutes to
complete.
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