NSES Content Standard C  Life Science: Populations and ecosystems Grades 5-8, page 157 Populations of organisms can be categorized by the function they serve in an ecosystem. Plants and some micro-organisms are producers--they make their own food. All animals, including humans, are consumers, which obtain food by eating other organisms. Decomposers, primarily bacteria and fungi, are consumers that use waste materials and dead organisms for food. Food webs identify the relationships among producers, consumers, and decomposers in an ecosystem.

 
Benchmark 5A The Living Environment: Diversity of Life
Grades 6-8, page 104
One of the most general distinctions among organisms is between plants, which use sunlight to make their own food, and animals, which consume energy-rich foods. Some kinds of organisms, many of them microscopic, cannot be neatly classified as either plants or animals.

Benchmark 5A The Living Environment: Diversity of Life
Grades 6-8, page 104
All organisms, including the human species, are part of and depend on two main interconnected global food webs. One includes microscopic ocean plants, the animals that feed on them, and finally the animals that feed on those animals. The other web includes land plants, the animals that feed on them, and so forth. The cycles continue indefinitely because organisms decompose after death to return food material to the environment.

Benchmark 5D The Living Environment: Interdependence of Life
Grades 3-5, page 116
Insects and various other organisms depend on dead plant and animal material for food.

Benchmark 5D The Living Environment: Interdependence of Life
Grades 6-8, page 117
Two types of organisms may interact with one another in several ways: They may be in a producer/consumer, predator/prey, or parasite/host relationship. Or one organism may scavenge or decompose another. Relationships may be competitive or mutually beneficial. Some species have become so adapted to each other that neither could survive without the other.