An ecosystem is a community of plants, animals, and smaller organisms that live, feed, reproduce, and interact in the same area or environment. Every single plant and animal could not exist alone on planet Earth. All living organisms need millions of other living organisms to survive. The way these organisms interact with the sun, soil, water, air and each other in a specific area is called an ecosystem. In the following paragraphs I will discuss the organizations that make up an ecosystem and their organizations. There are two main types of ecosystems aquatic and terrestrial. An aquatic ecosystem is in a body of water, where animals, plants, and their physical environment interact in the water. The two main parts of aquatic ecosystems are marine ecosystems and freshwater ecosystems. The marine ecosystem covers approximately 71% of the Earth's surface and can be divided into different zones and categories. The marine ecosystem area is divided based on the depth of the water and the characteristics of the coast. The oceanic zone is the open part of the ocean where animals such as sharks and whales live. The intertidal zone is the area between high and low tide and includes coral reefs, lagoons and salt marshes. The benthic zone where many invertebrates live. There are also thousands of species of plants living in the ocean such as kelp, seaweed, sea grass, and mangroves. (Mann KH 2006) Aquatic ecosystem is also classified as freshwater ecosystem. These include ponds, lakes, streams and rivers, streams and wetlands. Ponds and lakes are often called lentic ecosystems. This means they have still or stagnant water, not moving water like rivers or streams. Lakes are often divided into four zones of biotic communities: Littoral zone - Lim...... middle of paper ......ing.• Living beings are composed of cells that have a complex and organized structure.• Living things maintain their complex structures and their internal environment called homeostasis.• Living things respond to stimuli from their environment.• Living things have the ability to evolve.• Living things acquire energy from their environment and convert it in different forms.• Living things grow.• Living things reproduce.If something follows one or only some of the rules listed above, it does not necessarily mean it is living. To be considered alive, an object must possess all the characteristics of living things. For example, a virus may be seen as a living thing because it has the ability to make someone seriously ill, but in reality viruses are not living things. Viruses do not reproduce, have no energy and do not respond to stimuli. (Audesirk T. 2011)