How Matter Moves Through an Ecosystem

The laws of conservation of energy and mass state that energy and matter are never lost or gained—but they do change forms.

We have already seen that while energy does not cycle through an ecosystem, certain chemical nutrients do. In other words, matter gets used over and over and over again.

Watch this video, which documents the varied interactions that occur in a freshwater ecosystem. As you watch, notice how matter passes through the food web and into and out of the air, water, and soil, and how it is combined and recombined in different ways. After watching, review the information about biogeochemical cycles in the box below, and respond to the questions under Take Notes.

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Video: Follow That Nutrient | UNC-TV Quest

Biogeochemical Cycles

Plants absorb chemical nutrients from the soil, and these nutrients are subsequently passed on through the food chain. But it doesn’t end there.

Through mechanisms that change the configuration of molecules, including respiration, digestion, and decomposition, living things release these chemical nutrients back to the physical environment, where they enter into the atmosphere, the oceans, and even rocks. Since the chemicals move through both the living (biological) and the nonliving (geological) world, we call these kinds of pathways biogeochemical cycles.

The four main biogeochemical cycles are the water cycle, the carbon cycle, the nitrogen cycle, and the phosphorous cycle. Using the water cycle as an example, this cycle captures the complete journey that water makes, from one place to the other, and from one state to the other. As the word "cycle" suggests, there is no starting or ending point. You can begin at any point and trace a path back to where you started.

Take Notes

What are some common student conceptions about nutrient or biogeochemical cycles that you see in your classes?
How would you use this type of media to support your teaching about matter in ecosystems?

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