Ecology is the study of how living things interact with each other and with their environments. Those interactions involve cycling of chemical elements and the one-way flow of energy.
Processes occurring at the cellular level affect the entire biosphere. The diversity of life on earth is a function of the ecological processes that have driven evolution.
The study of ecology has many components. Among these components are the levels of organization in the biosphere. Ranging from molecules to ecosystems, each level of the biosphere interacts with every other.
On a small scale, a single grain of sand weighs almost nothing. A bucketful would weigh several pounds. The sand on a stretch of beach would weigh many tons. Although the scale has changed, sand is still being measured. Cells and the biosphere are measured through different scales.
Individual organisms are composed of organic molecules. Autotrophic organisms such as plants use molecules of inorganic carbon dioxide and soil nutrients to produce biomass.
Biomass is simply living material. Heterotrophic organisms produce biomass by feeding on other organisms. As organisms use energy through metabolism, inorganic molecules such as carbon dioxide and water are released. When organisms die, biomass breaks down and molecules of matter are recycled through the biosphere.
Individual organisms reproduce to form populations. A population is a group of organisms of the same species interacting in a given area. Some populations are composed of scattered individuals that only interact with each other to reproduce sexually. Other populations are composed of groups of individuals that interact closely.
Communities are all the populations of various species interacting in a given area. For instance, a pond may contain a population of the frog species Rana catesbeiana (bullfrogs). The same pond might also be home to the plant Typha latifolia (the cattail). A frequent visitor to the pond might be Egretta thula, a water...