Life Science: Session 7
What is a community?
Communities are populations of organisms that interact with each other. As with each level of organization in the living world, certain phenomena in a community act to shape and sustain it. The interactions among different populations are what hold a community together. Some interactions involve the provision of habitat. A good example is a tree that houses birds, insects, and other creatures. Other vital interactions involve reproduction, such as plants that are pollinated by insects. Symbiotic interactions, such as the relationship between algae and fungi in lichens, are also important.
Without a doubt, the most important interactions in a community involve energy flow — the transfer of energy along food chains from one organism to the next. Without this flow of energy, individual organisms cannot survive and the community collapses.
How does energy flow in a community?
In any community, there are the producers, consumers, and decomposers. Producers include plants and some protists, bacteria, and archaea. These individuals take in energy in an inorganic (i.e., nonliving) form, such as light, and change it into food, which is an organic form of energy. This energy is used or stored in the organic molecules that compose a producer’s body.
Consumers are organisms that can’t make their own food. The most familiar consumers to us are animals. They represent the “typical” consumer in that they ingest food to obtain energy. Some animal consumers eat plants, some eat other animals, and some eat a variety of food sources. Certain protists, like the amoeba, are also consumers.
A special group of consumers is the decomposers. Like other consumers, they can’t make their own food. They differ from other consumers because they obtain their energy by decomposing the bodies of dead things. They secrete digestive chemicals onto their food and break large molecules into smaller ones that they then absorb. The most important decomposers in most communities are the fungi and the bacteria. Some protists and archaea are also decomposers.
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