What makes things alive?
CRITERIA FOR LIFE
Learning Goals
 I can determine if something is alive based on
the criteria for life.
 I can describe the history of life on Earth.
 I can describe how organisms are classified by
biologists.
 I can determine which kingdom an organism
belongs to based on its characteristics.
Criteria for Life
 In order for something to be considered alive:
 It must be made of cells
 Must use energy
 Grow and develop
 Reproduce
 Adapt to its environment
 Maintain Homeostasis
Criteria for Life
 Made of cells
 Life is either multicellular or unicellular
 Multicellular – made of many cells
 Unicellular – made of one cell
 2 types of cells
 prokaryotic
 eukaryotic
Criteria for Life
 Grow and Develop
 Change over time
 Gain size, characteristics, etc
 Reproduce
 Be able to reproduce with in its own species
 All life comes from other life
Criteria for Life
 Adapt to its environment
 Respond to environmental stimuli
 Both individually and evolutionarily
 Maintain Homeostasis
 Maintain an internal balance
Where did all of this come from?
HISTORY OF LIFE
The Origin of Life
 Age of the Earth
 4.5 billion years old
 Life has been around for 3.5-4 billion years
 Many ideas
 Most can not be supported by scientific
evidence
 Many are our best guess
 Most agree that life began when nonliving
materials organized into molecular aggregates
 Produced abiotically
 Made when organic molecules began to glom together
Origin of Life
 Other ideas
 Spontaneous Generation
 Old thought that life would come from nonlife
 Disproven by Pastuer
 Biogenesis
 Life can only arise from other life
 So something must have put it here.
 RNA is believed to be the first genetic material
Evidence
 Fossils
 Preserved specimens of tissue that was once alive
 Usually found in sedimentary rock
 Shows change in organisms on Earth
throughout history Organized into the
geologic time scale
 Broken into eons, eras, periods, and epochs.
 Based on the life that lived during that time
Evidence
 Dating of Fossils
 Relative dating – bottom layer is older than
the one above
 Radioactive dating
 Radioactive elements breakdown at a specific rate
 Based on the element
 Each element has a half-life
 time it takes for half of the original to break down

Evidence
 Other evidence
 Continental Drift
 Slow movement of continents throughout time
 explains how similar fossils can be found on
continents now separated by oceans.
Classifying Life
TAXONOMY
The Diversity of Life
 Scientists have identified and named
approximately 2.5 million species!!
 Many believe there are as many as 20 million
species alive today!!! Now add in all of the
species that have become extinct over the
history of earth, the numbers have now risen
to over 500 million species in just the last 500
million years
Why Classify?
 Scientists need a way to organize all of these
organisms in order to distinguish one from
another.
 A universal language needed to be
developed, so scientists from around the
globe could understand one another.
Linnaeus
 In 1735, Swedish botanist Carl Linnaeus
thought there should be a way for standard
way for science to name organisms. He
developed a system of naming plants that is
still used today (with many changes.)
Linnaean System
 The system created by Linnaeus placed
organisms into a hierarchy.
 In this hierarchy, the farther you went up, the
more general and larger the groups were.
 The smallest most specific group is the species.
 The largest, most general group is called the
Kingdom.
Linnaean System
 As you travel down the hierarchy, the groups
get more specific. This leads to a system
called Taxonomy.
 Each group, taxa, has specific characteristics
that separate them from the others.
Linnaean System
Kingdom
Phylum
Class
Order
Family
Genus
Species
Animalia
Chordata
Mammalia
Primates
Hominidae
Homo
sapiens
New division
 A new division was recently added due to
evolutionary (DNA) evidence.
 Domain
 Large category that includes several kingoms
 Archaea – prokaryotic cells that tend to live in
extreme environments
 Believed to be most like ancient, earliest life
 Bacteria – newer prokaryotic organisms
 Eukaryota – all eukaryotic organisms
Binomial Nomenclature
 The Linnaeus system of naming required a
two word, Latin name for each species.
 This is called Binomial Nomenclature.
 Each name contains the genus and the
species name for that organism
 Ie. Homo sapiens
Species
 Species is the only taxa with real biological
definition.
 All members of a species share a gene pool.
 They can interbreed and create viable offspring.
(offspring that can reproduce)
 Every other taxa is less definite and subject to
debate.
The Six Kingdom System
 Organisms on Earth have been classified into one
of five kingdoms.
 Each kingdom has different characteristics.
 The Six Kingdoms
 Animalia
 Plantae
 Fungi
 Protista
 Archaea
 Bacteria
Archaea
 The oldest (evolutionarily) of all organisms
 Characteristics
 Unicellular
 Prokaryotic
 Examples
 Halophiles
 Extremophiles
 methanogens
Bacteria
 Characteristics
 Unicellular
 Prokayotic (no nucleus)
 Examples:
 Bacteria
 Blue-Green Algae
Protista
 Characteristics
 Unicellular
 Eukaryotic (cells have a
nucleus)
 Examples:
 Plankton
 Ameba
 Paramecium
 Algae
Fungi
 Characteristics
 Multicellular (mostly)
 Eukaryotic
 Obtains Food (heterotrophs)
 Cell walls made of Chitin
 Can not move on its own (sessile)
 Examples
 Mushrooms
 Yeast
 Molds
Plantae
 Characteristics





Multicellular
Eukaryotic
Makes it own food (autotrophic)
Cell walls made of cellulose
Can not move on its own (sessile)
 Examples:
 Trees
 Ferns
 Moss
Animalia
 Characteristics:




Multicellular
Eukaryotes
Heterotrophs
No cell walls
 Examples




Humans
Sponges
Insects
Birds