OpenSciEd 7.5 Ecosystem Dynamics Practice Test

Biogeochemical cycles move essential elements through living things and the nonliving parts of Earth, linking organisms to air, water, and rocks. Through processes like photosynthesis, organisms take carbon dioxide from the air and water from their surroundings to build organic matter, storing energy from sunlight. In respiration, those organisms release some of that carbon back to the air as CO2, releasing the energy they used to grow and survive. Decomposition recycles nutrients from dead matter back into soil and water, making them available again for other organisms. Weathering of rocks releases minerals into soils and waters, supplying nutrients that living things need. All of these steps connect the biosphere with the lithosphere, atmosphere, and hydrosphere, showing how matter moves through different reservoirs across the planet. It’s important to keep in mind that energy flow and matter cycling are related but distinct. Energy from the sun drives the chemical changes in photosynthesis and respiration, but the cycles themselves are about moving elements through different reservoirs, not about the one-way transfer of energy. The other descriptions are incomplete because they either narrow the focus to a single element or to living things only, or they claim cycles don’t relate to energy at all. The full idea is that cycles involve both living organisms and nonliving parts, moving essential elements through multiple parts of the Earth system.