Life: The property manifested in functions such as metabolism, growth, response to stimulation, and reproduction, by which living organisms are distinguished from dead organisms or from inanimate matter. (Webster's Dictionary)
Life: The state of being which begins with generation, birth, or germination, and ends with death; also, the time during which this state continues; that state of an animal or plant in which all or any of its organs are capable of performing all or any of their functions; used of all animal and vegetable organisms. (Gray's Medical Dictionary)
II. What Properties are Associated with Life? Life is difficult to define, but all living organisms are alike in these aspects:
1. Cellular Organization: All living organisms are composed of one or more cells - the basic unit of life ... "Life is Totally Cellular"
2. Growth and Development: All living organisms assemble matter (chemical elements) into simple or complex compounds, and use the energy derived from these compounds to grow and change over time. The process of using chemical energy to do cellular work is called metabolism.
3. Reproduction: All living organisms are programmed to produce new generations of cells or new multicellular organisms.
4. Response to Environment: All living organisms sense changes in their surroundings (using receptors) and make controlled responses (behavior).
5. Heredity: All living organisms possess a genetic system that is based on the replication of DNA, a complex double-stranded molecule that specifies the information to make cellular proteins.
III. Life is organized on many structural levels: At each level of organization, novel properties emerge that were not present at the previous level.
Biosphere - regions of air, water and soil on Earth where living organisms exist
Ecosystem - a community and its physical environment
Community - groups of different species living in the same area
Population - groups of individuals of the same species living in the same area
Multicellular Organism - an individual composed of cells arranges into tissues and organs
Organ System - groups of organs performing a common task
Organ - groups of tissues performing a common task
Tissue - group of specialized cells
Cell - Smallest living unit
Organelle - compartments inside cells
Molecule - 2 or more atoms bonded together
Atom - smallest unit of an element
Subatomic Particle - proton, electron, neutron
IV. Classifications of Life
There are at least 5 million and perhaps 10 - 30 million species on Earth!
6 to 7 million in tropics alone1.4 million species currently named and described260,000 plants, 50,000 vertebrates, 750,000 insects....
1. Kingdom Monera [10,000 species]: Unicellular and colonial-- true bacteria (eubacteria), archaebacteria*, and photosynthetic cyanobacteria (blue-green algae).
2. Kingdom Protista [250,000 species]: Unicellular protozoans and algae (unicellular & multicellular)
3. Kingdom Fungi: [100,000 species] Multicellular, generally heterotrophic mushrooms, molds, and fungi
4. Kingdom Plantae: [250,000 species] Multicellular photosynthetic organisms
5. Kingdom Animalia: 1,000,000 species] Multicellular animals, without cell walls and without photosynthetic pigments
*Currently 5 different Kingdoms are recognized; however, many scientists believe that the prokaryotic Archaebacteria belong in their in their own (6th) Kingdom
However, even with all this diversity.....all forms of life show unity in that they are all
Are based on the cellUse the same genetic code (DNA)Share similar or identical metabolic pathwaysShare similarities of cell structure
