How does matter move through an ecosystem?
When we speak of matter it literally refers to everything, animals, plants, water, air, rocks, soil, etc. So there are many ways you can describe matter moving through an ecosystem, it depends what matter you are interested in. Here I'll explain a little about organic matter, as in matter that contains carbon, oxygen and hydrogen, and in this case comes from living things.
In an ecosystem there is a hierarchy of feeding among the organisms called trophic levels, basically each level feeds on the one below it and plants form the base because they make there own food using light, water, and Carbon Dioxide.
As seen in the image below each level has a lot of energy and each layer has less than the one before. But in the end that top predator like the eagle, or human, shark, tuna, etc, will usually die without being killed and some animals of each level will also die. This dead matter will build up but luckily there are organisms that eat this, completing the cycle of organic matter.
Organisms that provide this clean up service include fungi, bacteria, insects, worms, all of which are in turn eaten by other trophic levels. The dead organic matter consumed by this clean up crew becomes soil which provides a place for plants to grow. As a result organic matter is always being recycled.
This is summarized below:
You can read more and review with questions and a video here: http://www.ck12.org/book/CK-12-Earth-Science-Concepts-For-Middle-School/section/11.16/
This is a great site to practice material and is free for students.