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What are the Levels of Organization in Biological Systems?


What makes something alive? It sounds like a simple question, but when you really delve into it the answer may not be obvious. Scientists have determined a list of traits that are shared by all living creatures: Living things are complex and made of one or more cells, they are able to respond to their environment, they have a genetic code, they can grow, reproduce, process energy, and maintain a consistent internal state (also known as “homeostasis”).


A cell is the smallest biological unit that is capable of possessing all the traits of a living organism. It is the least complex level of organization in biology. While cells can carry out all the same basic processes as more complex living organisms, their processes are smaller and more simplified.


A group of similar cells with the same function is called a tissue, and is the next level of biological organization. For example, a sample of muscle tissue might consist of many muscle cells that all have the same job of helping to move an arm or leg.


Many similar tissues combine to form an organ. Organs help perform vital functions that keep their organism alive. For example, your stomach breaks down the food you consume so that you can more easily get energy from it. Organs with interrelated jobs make up an organ system. Your stomach is part of your digestive system, which includes your mouth, intestines, colon, and even accessory organs like your gallbladder and pancreas. These organs all work together to digest food and provide your body with energy.


Of course, all the various organ systems of your body from your digestive systems to your nervous system carry out the various functions needed to keep your body alive. Together they make up an independent living organism.


All the organisms of a single species that live in a given area and interbreed are called a population. For example, all the American bison living in Yellowstone National Park make up a single population of bison. Yellowstone also contains populations of many other organisms, like trees, elk, insects, grasses, and wolves. Together, these populations make up the Yellowstone community. A community is made up of all the populations of living organisms found in a particular area.


However, a community only takes into consideration the living aspects of a particular area. The Yellowstone ecosystem encompasses all the living organisms found in the park as well as all the abiotic, or non-living, aspects like the soil, rocks, and rivers.


















(WikiImages, 2005)


All the ecosystems across the entire world are known as the biosphere. The biosphere includes all living things on our planet, as well as all the abiotic features that those organisms rely upon for life. The cell is the lowest level of biological organization and the biosphere is the highest.


Image Citation:

WikiImages (artist). (2005). Earth Blue Planet Globe [digital art]. Retrieved from

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