Ecosystems Curriculum

Section 2: Background Information

Matter Recycling and the Conservation of Matter

Matter is neither created nor destroyed, but it can be changed into new forms. Matter in the non-living world can enter the living world through plants. As matter then moves through a food web, it becomes reorganized and is incorporated into the bodies of the living things that take it in. When something dies and decomposes, matter does not disappear but is broken down and recycled into the ecosystem (though not necessarily the same ecosystem). Decomposition, carried out by decomposers, is the process of breaking down dead matter into basic substances that can then be used again by new living things. The nutrient cycle is the way in which nutrients move between living things and the physical environment. It is the intake of basic substances (like CO₂ and H₂O) from the physical environment by plants, the consumption of food in the form of plants and animals, the release of waste and other by-products of life processes by all organisms, and decomposition of any dead thing by decomposers. It can be challenging for students to grasp the idea of conservation of matter. They do not necessarily believe that matter is conserved and are comfortable with explanations that involve dead material drying up, blowing away, and disintegrating till there's nothing left, for example.

Cyclic Causality and Decay

The activities in this section introduce students to the cyclic causal pattern involved in decay. It can be difficult to talk about cyclic patterns. Typically we break them down into linear patterns to talk about what happens, and so we lose the fundamental circular aspect (which cannot be reduced further). In cyclic causal forms, no single event is the cause of what happens, rather events are both causes (of other events) and effects (of other events). In some curricula, decomposers are introduced as the end of a food chain. Decomposers ARE the end of the food chain in terms of being the end point of energy flow. They are NOT the end of a nutrient cycle because the matter can be used again. The activities in this section underscore that the relevant causal pattern is a circle, not a line. Decomposition is always occurring. Students need to realize that there are many things decomposing simultaneously in different states of decay. There are many simultaneous circles of decay. Matter is being recycled. Energy is not. New energy enters the system from the sun.