Introduction, Characteristics of life

January 10, 2000

Readings: Starr text: Ch 1 front page, 1.1, 1.2, 1.4

The most beautiful thing we can experience is the mysterious. It is the source of all true art and science". -- Albert Einstein

Outline, Chapter 1 - Themes and Concepts in Biology

I. Biology is the study of life

II. Some definitions of Life

III. What Properties are associated with Life?

IV. Life is organized on many structural levels

V. Intro into the Classification of Life

Chapter 1 - Themes and Concepts in Biology

I. Biology is the study of life. It is a human endeavor that results from our attraction to life in all its forms (E.O. Wilson's biophilia)

II. Some Definitions of Life:

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)

Life: As described in the Catholic Encyclopedia - just for those interested in a more philosophical definition...

III. 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.


IV . Life is organized on many structural levels: At each level of organization, novel properties emerge that were not present at the previous level. (Figure 1.2)

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

V. Intro into the Classification of Life = The Five Kingdoms (or is it 6?)

The Amazing Diversity Of Living Systems: How Many Species Are There?

There are at least 5 million and perhaps 10 - 30 million species on Earth!

6 to 7 million in tropics alone
1.4 million species currently named and described
260,000 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 cell
Use the same genetic code (DNA)
Share similar or identical metabolic pathways
Share similarities of cell structure

Exercise: Viruses: Alive or not?!? A special case.
Scientists do not agree whether viruses are alive or not.

A virus consists of DNA (or a related molecule, RNA) wrapped with a protein "coat" and sometimes an outer envelope "borrowed" from its host cell.

The coat can consist of hundreds of proteins arranged in symmetcical, complex patterns

Viruses do not have organelles or cytoplasm

Viruses are parasites of other cells - that is the only way they can reproduce.


1. In what ways of the 5 we discussed could viruses said to be "alive"?


2. What components do viruses lack that are shared by other living organisms?


3. Are viruses "alive" or not?



Objectives - Ch 1: Characteristics of Life. Be sure you are able to

1. List Characteristics that distinguish living organisms from non living objects
2. List the levels of chemical / biological organization from simple to complex, and list a structure found at each level
3. Explain the 5 Kindgoms and list a representative organism for each kingdom

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