Final answer:
The list that does not follow the natural food chain is 'grass, raccoon, mouse' as it improperly orders the trophic levels by placing the raccoon, a secondary consumer, before the mouse, a primary consumer. A natural food chain shows the flow of energy from producers to apex predators or decomposers, where decomposers can be included to represent nutrient recycling.
Step-by-step explanation:
A food chain is a linear representation of how different organisms in an ecosystem feed on each other. It shows the flow of energy and nutrients from one organism to the next, beginning with producers and ending with apex predators or decomposers. In a food chain, each organism occupies a specific trophic level. Producers, like algae and grass, are at the first level; primary consumers, such as krill and mouse, feed on these producers. Secondary consumers eat primary consumers, and so on.
One of the lists provided by the student does not follow the natural order of a food chain: grass, raccoon, mouse. Typically, a raccoon is a secondary consumer that would eat smaller animals such as mice, which are primary consumers. Grass, as a producer, would support animals like mice rather than raccoons directly. Therefore, this sequence is incorrect as it does not represent a natural flow of energy in an ecosystem.
Regarding the inclusion of decomposers in a food chain, they can certainly be added to depict the recycling of nutrients back into the ecosystem. Decomposers, such as fungi and bacteria, break down dead organisms and waste, returning important nutrients to the soil where they can be used by producers, thereby completing the cycle.