Final answer:
Primary consumers are the organisms that do not make their own food and get it from producers, such as herbivores that eat plants. Decomposers consume dead organic material from all trophic levels and recycle nutrients, differentiating them from tertiary consumers.
Step-by-step explanation:
The organisms that do not make their own food and receive it from producers are known as primary consumers. These are typically herbivores that feed directly on producers such as plants or phytoplankton. In contrast, secondary consumers are usually carnivores that eat the primary consumers, and tertiary consumers are carnivores that eat other carnivores. Decomposers, on the other hand, break down dead organic material from all trophic levels and are crucial for recycling nutrients back into the ecosystem.
Decomposers differ from tertiary consumers because they consume dead components of each trophic level, while tertiary consumers typically feed on living prey. Decomposers play a vital role in sustaining the ecosystem by breaking down dead matter and returning nutrients to the soil or water, which can then be used by primary producers.