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Levels of Hierarchy of Biological Organization

Creating a hierarchy is a way or organizing information and concepts. Hierarchies exist in a wide range on systems. They all have one thing in common: Hierarchies go from simplest to most complex. In Biology, there are a wide range of living objects. The task of biologists is to create order out of such disparate living things as bacteria, elephants and apple trees. The concept of hierarchy helps biologists and biology students arrange different types of biological organisms.

Nested Hierarchy
- There are several different ways to organize a hierarchy. Two of the most popular means are nested and non-nested hierarchies. Nesting hierarchies mean that one level of hierarchy fits inside the next highest level. For example, one biological hierarchy starts with molecules, then cells, tissue, organ and the hierarchy builds. Every type of tissue is made of cells, and all organs are made of tissue that is made up of cells. Each level of the hierarchy contains the lower levels.
Non-Nested Hierarchy
- Nesting hierarchy works well for a wide range of systems, but it doesn't fit all forms of life and how they relate to each other. Food webs, for example, are intricate hierarchical systems, but they aren't nested. A lion may prey on an antelope, but so may parasites and scavengers. In some cases, more than one organism feeds on the prey at the same time.
Biological Hierarchy
- One common biological hierarchy moves from least complex to most complex. It starts with the molecule. Several molecules together form a cell and cells work together to create tissue. Organs comprise one or more types of tissue and work within an organ system. An organism is one individual from any species. A population is a local group of that species and it works within a community of all different species in the area. The entire area is called the ecosystem.
Problems with Hierarchies
- While this common biological hierarchy works well in most areas, there are problems. For example, Prions exist and biologists see the effects of the organisms. But they are molecular, like a chemical, not cellular, like a bacteria. So an individual prion jumps from molecule to organism then to population as it reproduces. In addition, some molecules are so common that they are almost ignored in the hierarchy. Carbon is present in all living organisms from simple single cells to large animals.
  
  Another issue is that as biologists move up the hierarchy, they can move into an even larger hierarchy. For example, when looking at the ecosystem of the yeast organism, that ecosystem might be the digestive tract of a human being. The human being, in turn, is part of a larger population, community and ecosystem.

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