Ecosystem model (described): In a pond ecosystem, algae (living) take in matter from pond water (nonliving) and from the air (nonliving). A snail (living) eats algae. A fish (living) eats snails. When organisms die, bacteria and fungi (living decomposers) break down dead matter. Matter from decomposers becomes part of the pond mud (nonliving). Arrows are labeled:
- water matter algae
- air matter algae
- algae matter snail
- snail matter fish
- dead matter decomposers
- decomposer matter pond mud The model states: Matter cycles through ecosystems.
Which statement about matter movement is supported by evidence from the ecosystem model?
- Matter only moves between living organisms; nonliving parts like water, air, and mud do not take part in matter movement
- Matter moves randomly in any direction, so the arrows do not provide evidence about where matter goes
- Matter from dead organisms can move into decomposers and then become part of a nonliving part of the ecosystem (pond mud) (correct answer)
- Matter is created when algae grow, so more matter exists in the ecosystem over time
Explanation: The core skill in tracing matter in ecosystems is analyzing models to find evidence of how matter flows between components. Matter moves through ecosystems by entering from nonliving parts like water and air into producers, then to consumers and decomposers, eventually returning to the environment. Models illustrate cycling with arrows labeled to show matter transferring, such as from dead organisms to decomposers and then to pond mud. A useful checking strategy is to evaluate each statement against the arrow directions and labels in the model for support. One misconception is that matter is created anew by growing organisms, but matter is conserved and only rearranged. By tracing matter, we understand how ecosystems maintain balance through recycling. This generalization highlights that ecosystem functioning depends on matter's perpetual circulation.