Webster’s Seventh New Collegiate Dictionary

• : ancestry, parentage
• : rise, beginning, or derivation from a source
• : the point at which something begins its course or existence
• : applies to the things or persons from which something is ultimately derived and often to the point where something springs into being

• a : the quality that distinguishes a vital and functional being from a dead body or purely chemical matter
• b : the state of a material complex or individual characterized by the capacity to perform certain functional activities including metabolism, growth and reproduction

• Key characteristics shared by living things
• what is life?
• Many ideas about the origin of life
• ideas about the origin of life
• what the early earth was like
• testing the spontaneous origin hypothesis
• The first cells
• origin of cells
• the earliest cells - bacteria
• The first eukaryotic cells
• The kingdoms of life

• There are many ideas about the origin of life
• ideas about the origin of life
• can’t definitively answer question of how life originated
• its impossible to go back in time and observe life’s beginnings
• some questions about life’s origins can be answered from evidence in rocks
• other questions cannot be answered at this time
• in general, there are three possible explanations for the origin of life

• ideas about the origin of life
• three possible explanations for the origin of life
• special creation
• extraterrestrial origin
• spontaneous origin

• special creation
• the hypothesis that life forms were put on earth by supernatural or divine forces
• hypothesis of divine creation is at the core of most major religions
• oldest and most widely accepted hypothesis
• considered an "unscientific" explanation
• because it cannot be tested and potentially disproved
• assumes forces operating in the past are different than those operating today

• extraterrestrial origin
• hypothesis that life did not originate on earth but was carried to earth by meteors or cosmic dust as an extraterrestrial "infection"
• cannot be rejected based on evidence currently available to science
• recent discovery of possible fossils in Mars rocks
• recent discovery of liquid water under surface of Jupiter’s ice-shrouded moon Europa
• however, also considered an "unscientific" explanation because it cannot be tested and potentially disproved

• spontaneous origin
• the hypothesis that life evolved from inanimate matter, as associations among molecules became more and more complex
• in this view, the force leading to life was selection
• as changes in molecules increased their stability and caused them to persist longer, these molecules could initiate more and more complex associations
• this culminated in the evolution of cells

• spontaneous origin
• this view is not definitely the correct one
• this view does not preclude the other two possibilities
• that a divine entity may have acted via evolution
• that life may have infected the earth from some other world and then evolved

• spontaneous origin
• this view is considered the only "scientific" explanation of the three because it is the only one that can be tested and potentially disproved
• as such, it is the only explanation to be focused on in this text and in this course

• spontaneous origin
• the goal is attempting to understand whether
• the forces of evolution could have led to the origin of life and, if so
• how might the process have occurred

• What is life?
• What qualifies something as "living"?
• must distinguish between necessary and sufficient criteria
• necessary criteria
• possessed by all life
• sufficient criteria
• possessed only by life

• What is life?
• four possible criteria of life
• movement
• sensitivity (responding to stimuli)
• death
• complexity

• four possible criteria of life
• movement
• not necessary
• not all living plants and animals move
• not sufficient
• non-living clouds do move
• sensitivity (responding to stimuli)
• not necessary
• kicking a redwood tree
• not sufficient
• non-living street light w/ photo cell responds to light

• four possible criteria of life
• death
• necessary
• all living things die
• not good criterion because of circular definition
• complexity
• necessary
• all living things possess complexity
• not sufficient
• many non-living things, like computers, all possess complexity

• All organisms on earth exhibit these 7 fundamental properties
• cellular organization
• sensitivity
• growth
• development
• reproduction
• regulation
• homeostasis
• heredity

• cellular organization
• all organisms consist of one or more cells
• complex, organized assemblages of molecules enclosed within membranes
• sensitivity
• all organisms respond to stimuli
• not all organisms respond to stimuli in the same way

• growth
• all living things assimilate energy and use it to grow via a process called metabolism
• all life on earth is based upon the transfer of the energy in covalent bonds
• resulting from the ability of plants, algae and some bacteria to carry out the process of photosynthesis
• in which carbohydrates, with energy-storing covalent carbon-carbon bonds, are created from CO₂ and H₂O using energy from the sun

• development
• multi-cellular organisms undergo systematic, gene-directed changes as they grow and mature

• reproduction
• all living things reproduce, passing on traits from one generation to the next
• no organism lives for ever, as far as we know, although some organisms can live for a very long time
• since all organisms die, ongoing life is not possible without reproduction

• regulation
• all organisms have regulatory mechanisms that coordinate internal processes
• homeostasis
• all living things maintain relatively constant internal conditions, different from their environment

• heredity
• all organisms on earth possess a genetic system that is based on the replication of a long, complex molecule called DNA
• this mechanism allows for adaptation and evolution over time and for the distinguishing characteristics of living things

• exact composition of early earth and its atmosphere is not agreed upon by all scientists
• but some fundamental characteristics are agreed upon
• reducing atmosphere
• high temperatures

• some fundamental characteristics
• reducing atmosphere
• early atmosphere contained
• principally CO₂ and nitrogen gas
• significant amounts of water
• H atoms bonded to other light elements such as S, N, and C
• hydrogen gas
• little, if any, oxygen gas
• no layer of ozone (O₃) to protect from ultraviolet light

• some fundamental characteristics
• reducing atmosphere
• such an atmosphere called "reducing" atmosphere due to ample availability of hydrogen atoms and their associated electrons
• takes less energy than today to form the C-rich molecules from which life evolved
• today’s atmosphere is considered an "oxidizing" atmosphere, which contains app. 21% oxygen
• in today’s oxidizing atmosphere, the spontaneous formation of complex carbon molecules cannot occur

• some fundamental characteristics
• high temperatures
• between 4.6 and 3.8 billion years ago the surface of the earth was kept molten hot as a result of bombardment from rubble from the forming solar system
• around 3.8 billion years ago the bombardment stopped, temperatures dropped, ocean temperature was 49 to 88 ° C (120-190° F)
• between 3.8 and 3.5 billion years ago life appeared

• What kinds of molecules might have been produced on the early earth?
• the Miller-Urey experiment attempted to answer this question

• the Miller-Urey experiment attempted to answer this question
• by repeating the process
• assemble an atmosphere similar to that thought to have existed
• exclude gaseous oxygen from the atmosphere
• place this atmosphere over liquid water
• maintain this mixture at a temperature somewhat below 100 ° C
• simulate lightning by bombarding the mixture with energy in the form of sparks

• Results of the Miller-Urey experiment
• w/in 1 week, 15% of C originally present as methane gas (CH₄) was converted into other simple C compounds such as formaldehyde and hydrogen cyanide
• these compounds in turn combined to form molecules such as formic acid, urea, and the amino acids glycine and alanine, some of the basic building blocks of proteins
• in similar, later experiments, even the complex ring-shaped molecule adenine – a base found in DNA and RNA – was formed

• Theories about the evolution of cells
• the evolution of cells required early organic molecules to assemble into functional, independent units
• cells are essentially little bags of fluid
• every cells’ content differs from the environment outside the cell
• early cells may have floated along in an environment of "primordial soup" but its interior would have had a higher conc.of specific organic molecules

• Theories about the evolution of cells
• how did these "bags of fluid" evolve from simple organic molecules?
• most scientists believe bubbles were involved in this evolutionary step
• bubbles are spherical & hollow
• certain molecules spontaneously form bubbles in water (ex. phospholipids)
• the structure of the bubble shields the hydrophobic regions from contact with water

• Earliest evidence of life appears in microfossils
• fossilized forms of microscopic life

• Characteristics of earliest life forms
• small (1-2 nanometers)
• single-celled
• lacked external appendages
• little evidence of internal structure
• did not have nucleus
• in general, physically resembled today’s bacteria
• organisms with this general body plan are called prokaryotes ("before nucleus")

• Bacteria
• are now divided into two groups
• archaebacteria
• eubacteria

• Archaebacteria
• present day organisms that differ in form and metabolism from other living things
• are found in areas sheltered from evolutionary alteration
• unchanging habitats that resemble earth’s early environment
• these living relics are the surviving representatives of the first ages of life on earth

• Archaebacteria
• are found in extreme environments
• methanogens
• exist in warm, oxygen-free environments
• ingest CO₂ and H to produce methane
• unusual lipids in their cell membranes (which aren’t found anywhere else)
• extreme halophiles (salt lovers)
• extreme thermophiles (heat lovers)
• boiling waters of springs & deep sea vents

• Eubacteria
• are the second group of bacteria
• characteristics
• strong cell walls with peptidoglycan
• simpler gene architecture
• some evolved ability to photosynthesize
• cyanobacteria (formerly blue-green algae)
• appeared ~ 3 billion years ago, contributed to increasing atmosphere oxygen concentration

• Eukaryotes
• eukaryote means "true nucleus"
• first appeared ~ 1.5 billion years ago
• are larger than bacteria
• have internal membranes, membrane-bound structures including nucleus
• they rapidly evolved to produce the diverse life forms that inhabit the earth today
• all organisms other than bacteria are eukaryotes

• Endosymbiont theory
• suggests that a critical stage in the evolution of eukaryotic cells involved symbiotic relationships with prokaryotic organisms (bacteria)
• energy producing bacteria may have come to reside within larger bacteria, eventually evolving into mitochondria
• photosynthetic bacteria may have come to reside within larger bacteria, eventually evolving into chloroplasts
• flagellated bacteria may have come to reside within larger bacteria, eventually evolving into motile eukaryotes

• Support for the endosymbiont theory
• observation of many symbiotic relationships
• observation of DNA in organelles
• many organelles have their own DNA
• mitochondria
• chloroplasts
• centrioles
• organelle DNA is remarkably similar to bacterial DNA in size and character

• Levels of organization of life
• non-living components of life
• atom
• molecule
• within cells
• macromolecule (biological)
• organelle
• cell

• Levels of organization of life
• within multicellular organisms
• tissue
• organ
• organ systems

• Levels of organization of life
• among organisms
• species
• population
• community
• ecosystem
• biosphere
• ecosphere

• Levels of organization of life
• these levels represent a hierarchy
• each level is built of parts at successively lower levels of organization

• The diversity of life can be arranged into three domains

• The diversity of life can be arranged into three domains
• how we classify organisms

• Millions of different organisms inhabit our planet
• To make some order of this diversity, biologists have developed a system of classification
• Taxonomy is the science of classifying and naming organisms
• 300 years ago, scientists first began to develop an overall classification system for organisms

• The binomial system
• developed by Swedish biologist, Carl Linnaeus (1707-1778)
• he gave a two-part (binomial) name to each species
• the names of genera (genus, singular) were the basic point of reference in classification systems
• and these names eventually came to be written in Latin

• A system based on a unique two-part name for each organism (hence bi - nomial)
• First part of name designates the genus, the second part the species
• Species name always used together with full or abbreviated genus name preceding it
• Genus is capitalized, species is not, both are underlined or italicized

• Examples
• Homo sapiens or H. sapiens (human)
• Quercus alba or Q. alba (white oak)

• The taxonomic heirarchy
• in the decades following Linnaeus, taxonomists began to group genera into large, more inclusive categories known as families
• membership in these families was intended to reflect perceived relationships between the genera included
• the taxonomic system was eventually extended to include several, more inclusive units

• Species are grouped to form a genus
• Genera (plural of genus) are grouped together to form a family
• Families are grouped to form orders
• Orders are grouped to form classes
• Classes are grouped to form divisions (fungi, plants) or phyla (protists, animals)
• Phyla (divisions) grouped into kingdoms

• All organisms are grouped into a few major categories
• the earliest classification systems recognized only two kingdoms of living things
• animal kingdom
• plant kingdom
• as biologists discovered new organisms and learned more about existing ones, kingdoms were added in recognition of the fundamental differences being found

• as biologists learned more about the Archaebacteria it became clear that this ancient group was very different from other living organisms
• to reflect these significant differences, biologists are increasingly adopting a classification system that recognizes a taxonomic level higher than kingdom
• three domains
• Archaea
• Bacteria
• Eukarya

• How many kingdoms?
• most biologists now use a six-kingdom classification system first proposed by Carl Woese of the University of Illinois
• all "life" currently classified into 6 kingdoms
• Archaebacteria
• Eubacteria
• Protista
• Fungi
• Plantae
• Animalia

• Prokaryotic kingdoms
• Archaebacteria
• Eubacteria
• Eukaryotic kingdoms
• Protista
• Fungi
• Plantae
• Animalia

• Domain Archaea
• Kingdom Archaebcateria
• Domain Bacteria
• Kingdom Eubacteria
• Domain Eukarya
• Kingdom Protista
• Kingdom Fungi
• Kingdom Plantae
• Kingdom Animalia

• Domain: Eukarya
• Kingdom: Animalia
• Phylum: Chordata
• Class: Mammalia
• Order: Primates
• Family: Hominidae
• Genus: Homo
• Species: sapiens

• Unity in diversity
• All forms of life have common features
• Life is diverse, but there are common themes that all living things exhibit

• All forms of life have common features
• Basic characteristics of life
• order
• cellular organization
• movement
• growth and development
• reproduction
• regulation
• ability to evolve and adapt as a population

• All forms of life have common features
• Basic characteristics of life
• order
• complexity - high degree of organization
• cellular organization
• cell theory
• sensitivity
• responsiveness to stimuli
• movement

• All forms of life have common features
• Basic characteristics of life
• growth and development
• reproduction
• regulation
• coordination of an organisms internal functions
• homeostasis
• metabolism
• ability to evolve and adapt as a population

• Evolution explains the unity and diversity of life
• theory of evolution explains the unity and diversity of life
• theories are much broader in scope than hypotheses and have much greater explanatory power

• Evolution explains the unity and diversity of life
• Darwin showed that evolution can explain the diversity of life and the underlying commonalities of life’s diversity

• Living organisms and their environments form interconnecting webs

• Living organisms and their environments form interconnecting webs
• living organisms do not exist in isolation
• an organism’s environment includes both living and non-living components

• Living organisms and their environments form interconnecting webs
• plants, some prokaryotes and protistans make food from carbon dioxide, water and the energy of the sun
• via the process of photosynthesis
• all animals ultimately depend on these photosynthetic organisms for food
• decomposers help recycle organic matter back to photosynthetic organisms

• Living organisms and their environments form interconnecting webs
• relationships among the living and non-living components of an ecosystem can be illustrated as a web