Transcript What is Life?

What is Life?
What is the definition of life?
• There have been many definitions of life created
over the years. There has yet to be a definition
that has been broadly accepted.
• We need to understand what qualifies matter as
living if we are to find life elsewhere in the
Universe.
• Can life exist somewhere other than earth? If so,
where? Would it be anything like earth life?
In 1976, NASA landed two Viking landers on
Mars in hopes of finding life on the planet
Viking Lander analyzing soil samples
Viking Biological Experiments
• The Gas Exchange Experiment (GEX) involved
injecting gases (O2, CO2). into a test chamber containing
a soil sample. Looking for changes in the makeup of
gases in a test chamber that might indicate that the
gases were taken up by living things.
• The Labeled Release Experiment (LR) was set up to
detect the uptake of a radioactively-tagged liquid nutrient
by living things. The idea was that gases emitted by
these living things would show the tagging indicating that
they consumed the nutrient.
• The Pyrolytic Release Experiment (PR) involved
"cooking" soil samples that had been exposed to
radioactively-tagged gases to see if the chemical had
been used by organisms to make organic compounds.
Results
Experiment
Response for
sample
GEX
no change
LR
labeled CO2
emitted
no organics
detected
PR
Response for
heat-sterilized
control
no change
none
no organics
detected
LR: The test sample released significant amounts of
radioactivity but was determined to be a false positive
Unifying Principles of Life
Evolution: living things change over time through natural
selection
Homeostasis: living things regulate their internal environment
Energy and Organization: living things are made up of highly
organized matter (cells) that use energy to carry out life
processes
Continuity: living things contain the genetic material DNA
which is passed from parent to offspring during
reproduction
Development: living things grow and develop over their life
Ecology: living things interact with their living and non-living
environment
Unifying Principles of Life
Can you find the unifying principles in
the above pictures?
Domains and Kingdoms of Life
Domain
Kingdom
# of cells
Type of
cell
Mode of
nutrition
Examples
Archaea Bacteria
Several
Eukarya
Several Protista Fungi Plantae
Animalia
Domains and Kingdoms of Life
Domain
Archaea
Bacteria
Kingdom
Several
Several
Protista
Fungi
# of cells
Unicellular
Unicellular
Uni or
Multi
Uni or
Multi
Multi
Multi
Type of
cell
Prokaryotic
Prokaryotic
Euk
Euk
Euk
Euk
Mode of
nutrition
Autotrophic
or
Heterotrophic
Auto or
Hetero
Auto or
Hetero
Hetero
Auto
Hetero
Eukarya
Plantae Animalia
Domains and Kingdoms of Life
• Archaea, bacteria, fungi, and plant cells have a cell wall
surrounding the cell membrane, but the structure of the
cell wall differs between each group (not homologous).
• Multicellular protists lack specialized tissues and organs
found in fungi, plants, and animals.
• Most autotrophy occurs via photosynthesis, but some
bacteria and archaea can use energy in chemicals to
make food.
• Heterotrophy occurs by ingestion (internal digestion) in
animals and absorption (external digestion) in fungi and
bacteria.
• Most animals have a nervous system and can move.
Domains and Kingdoms of Life
Prokaryotes vs. Eukaryotes
Prokaryote
Eukaryote
No nucleus (DNA not enclosed)
DNA in nucleus
No membrane-enclosed
structures
Membrane-enclosed
structures
0.1-10 micrometers (µm)
10-1000 micrometers (µm)
Evolved 3.5 billion years ago
Evolved 1.5 billion years ago
Kingdoms: Bacteria, Archaea
Kingdoms: Protista, Fungi,
Plantae, Animalia
Size of life
Domains and Kingdoms of Life
Are Viruses Alive?