A Quick Look at the Levels of Biological Organization.
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The biosphere is the region on, below, and above the Earth's surface where life exists. Living things can be found well into the atmosphere, the deepest parts of the ocean, and at least in some areas, microbes live in rock several kilometers below the surface of the earth.


The Earth contains numerous ecosystems. Ecosystems are distingushable groups of species and the abiotic(non-living) components of the environment with which the living creatures interact. Examples of ecosystems include ponds, forests, prairies.


A community is all the populations of different species living and interacting together in a distinct area. (e.g: all the species in a prarie) Abiotic means the nonliving parts of this distinct area which interact with the community. These two make up the ecosystem. For instance the particles of sand silt or clay in prairie soil are abiotic components of the prairie ecosystem. 
Species is the technical name given for a kind of organisms for example all people are considered to be one species distinct from other primates based on common appearence and more importantly that all races can and do interbreed with each other. 
A population is group of freely interacting and breeding individuals of the same species. For example, all the bull frogs in a pond can be considered a population of bullfrogs. Typically populations are subdivided into smaller groups: a pack of wolves, pride of lions, colony of ants. 
The organism or individual is that level of biological organisation that has its own distinct existance as a complex, self reproducing unit. We are multicellular organisms in that we are made of many highly specialized cells which cannot exist independently of other cells in the organism. Many organisms are unicellular, that is consist of a single independent cell. 
Multicellular organisms, especially animals typically are organized into organ systems, groups of organs that function together to carry out broad sets of functions. For instance an organ system in humans is the digestive system. Some of the organs in the digestive system are the stomach, liver, small intestine, pancreas. 
Organs are groups of tissues organised together to carry out a particular set of functions. Organs typically have several kinds of tissue. The stomach has an inner lining of tissue that secretes digestive enzymes outside the stomach has several layers of muscle and connective tissue. 
A tissue is a group of distinct and similar cells that carry out a specific set of functions. For example, muscle tissue is for contraction. Connective tissue is tissue consisting of cells surrounded by a large amount of non living material. Nerve tissue is for the conduction of nerve impulses and secretion of specialised chemicals called neurotransmitters. 
The cell is the smallest unit of biological organisation that biologists consider alive. All true cells are surrounded by a plasma membrane, carry out complex chemical reactions, and are at least potentially capable of self reproduction. Cells come in a wide variety of shapes and sizes. Not all cells have a nucleus, but again all true cells have genetic material in the form of DNA.
Organelles("little organ") area specialised structures inside of a cell. Often organelles are "membrane bound" (surrounded by a plasma membrane) but not always! Examples of organelles you will be come familiar with are the nucleus, mitochondria, endoplasmic reticulum, chloroplast, cilium, vacuole. The line between organelles and molecular assemblies is not clear. Sometimes the ribosome is not considered an organelle because it's not a membrane bound structure. 
Molecular assemblies are large organised sets of molecular units that make up parts of organelles. For example one common macromolecular assembly is the microtubule which important in forming structures in the cell related to maintaining the cell structure or related to cell movement. The cell(plasma) membrane that surrounds many organelles, and the cell, is a highly organised molecular assembly. 

Macro molecules are large molecules consisting of many subunits. Good examples are starch molecules which consist of many glucose units,(Glucose is a simple sugar) and proteins some of which consist of 1,000 or more amino acids. amino acids and proteins.


By small molecules I mean those molecules that are the small building blocks from which larger molecules are made. Some of the basic building blocks include; glucose, glycerol, amino acids, fatty acids, nucleotides. Some of these smaller molecules have other functions than as building blocks. 
Atoms are the smallest unit of matter that have the chemical properties of a particular chemical element. Atoms of an element have the same number of protons and electrons but two atoms of the same element may differ in terms of the number of neutrons. Most of the atom is empty space, in the center is the nucleus with the protons and neutrons, "Orbiting" the nucleus are the electrons. 
Neutrons and protons are in the atomic nucleus. Protons have a positive electrical charge, neutrons have no charge. Electrons have a negative electrical charge. Electrons occurr in only certain energy levels or shells and only so many electrons can occupy each energy level. An important concept is that electrons can carry and release energy. The last subatomic particle you need is the photon. A photon is a packet of light energy. It has no mass moves at the speed of light and is associated with electrons in that electrons can absorb and release photons. 

 

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Revised 05/3/01 pgd