Nutrient Cycling in the Serengeti
Activity
Educator Materials
For each group or individual students:
• “Card Activity Instructions” document
• either version of the “Student Handout” (to be completed after the card activity)
• (optional) “Nitrogen Cycle Diagram” graphic
BACKGROUND
Although rainfall is important for plant productivity, nutrient availability is what allows plants to flourish. Some
nutrients are harder for plants to get; they are referred to as limiting nutrients because they limit a plant’s ability
to grow.
Nutrient cycles involve the movement of certain nutrients — such as carbon, nitrogen, and phosphorus —
between biotic and abiotic reservoirs in the ecosystem. In this activity, the abiotic reservoirs are the atmosphere
(a source of carbon) and soil (a source of nitrogen and phosphorus), and the biotic reservoirs are the plants and
animals that live in the ecosystem.
Nutrient cycling keeps ecosystems functioning and productive. This activity provides multiple examples of how
nutrients cycle in the Serengeti specifically. As shown in the activity, herbivores take in nutrients by eating plants
and return them to the environment through processes such as defecation, urination, and decomposition.
Microbes and decomposers, such as detritivores, transform the nutrients into forms that plants can take up. For
example, some microbes convert atmospheric N
2
, which cannot be directly used by plants, to NH
4
+
(ammonium)
or NH
3
(ammonia), which can be used by plants.
TEACHING TIPS
• The card activity can be used with groups of any size. The number of students in a group does not affect the
activity, since they are jointly completing one model.
• Each group may experience the activity differently based on how they shuffle their cards. For example, some
groups may draw a microbe card that enables nutrient uptake early. Others may not and have more limited
nutrient uptake. Allow groups to compare their experiences during the discussion after the card activity.
• You may need to emphasize that although only carbon, nitrogen, and phosphorus appear in this activity,
other nutrients (iron, sulfur, etc.) are also needed to support ecosystems and also undergo nutrient cycling.
• The card activity is intended to introduce students to and engage them with the concept of nutrient cycling.
Every process depicted on the cards is more complex in reality than it is portrayed in this activity. You should
be aware of, and may also wish to discuss with your students, some of the simplifications or caveats of the
card model. For example:
o C:N:P ratios in plants are highly variable and can even vary based on growing conditions. The ratio used
in the card activity is that of Panicum maximum, a typical savanna grass.
o In reality, microbial communities are highly diverse, and different groups of bacteria are responsible for
different stages of decomposition and nutrient release. (For more details, see the short BioInteractive
video Solving Crimes with the Necrobiome
.) The goal of this activity is for students to understand that
microbes play an essential role in the cycling of many nutrients. A rigorous review of microbiology is
beyond the scope of the activity.
o The activity includes multiple cards to represent different components of the nitrogen cycle, and the
effects of some components are greatly simplified for ease of use. For example, the denitrifying bacteria
cards do not have a direct impact on the card activity. However, denitrification does have an important
role in nitrogen cycling and is included for the sake of completeness.
• Two options are provided for the accompanying handout. The regular “Student Handout,” which requires
minimal prior knowledge, is recommended for a general high school audience. The advanced “Student
Handout,” which requires more prior knowledge (see the “Prior Knowledge” section above for details), is
recommended for AP/IB or undergraduate students.