Ch.1.4: CHARACTERISTICS OF LIFE
In order to be considered LIVING an organism must meet
all 8 of the following criteria:
 1. Made of cells, at least one
 2. Take in and use energy, (do work, produce waste)
 aka METABOLISM
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3. Respond to their environment
4. Grow, develop and die
5. Be highly organized
6. Maintain homeostasis
7. CONTAIN DNA to Reproduce more cells and more
organisms
 8. CONTAIN DNA so have a means to evolve (“adapt”
too easy to confuse with “respond)
Made of cells
 Cell Theory says that
 Cells are the basic structural and functional units of life
 All organisms have at least one cell
 Cells only come from pre-existing cells
 Cells must have at least
 1. cell membrane (defining boundary; keep things inside)
 2. cytoplasm (material inside cell)
 3. genetic material (DNA in the form of a chromosome)
 4. free ribosomes ( to make proteins for the cell)
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Viruses are “less than” a cell
Multicellular organisms vs. unicellular organisms
Prokaryotic cells vs. Eukaryotic cells
Plant cells vs. Animal cells vs. Bacteria cells
Cell Types
PROKARYOTIC CELLS
• Pro/pre/ before
• ‘karyo’ = center or kernel
• CM, cytoplasm, DNA and free
ribosomes
• Bacteria
• Must be single cell
• No nucleus made with nuclear
membrane to keep in the 1
chromosome
• No organelles that are made of
membranes; no internal membrane
structures or compartments
• May have cell wall
EUKARYOTIC CELLS
• ‘eu’ = true
• ‘karyo’ = center or kernel
• CM, cytoplasm, DNA and free
ribosomes
• Plants, Animals, Fungi and Protista
• Can be single cell (mildew and algae)
can be multicellular (people = 30
trillion)
• Nucleus made of nuclear membrane to
keep in the many chromosomes
• Lots of membrane bound organelles
that make compartments like
endoplasmic reticulum and vacuoles
and mitochondria
• Some have a cell wall
Take in energy
METABOLISM
Maintaining life requires constant energy
Photosynthesis provides energy for food
web (solar energy becomes chemical
energy when trapped and stored as sugar)
Autotrophic plants make their own “food”
Heterotrophic organisms must eat
Waste is given off – CO2, NH4 and heat ,
sweat, urine/feces, even oxygen (plants)
Energy is used to do WORK
Respond / Interact (don’t confuse with Adapt)
 Respond means react
Respond to internal environment (low blood sugar, tired
and hungry)
Respond to external environment (predator/ prey)
 Immediate and short term compared to
adaptations
 Senses
 Stimuli – something that an organism respond to
 Examples: groan when alarm clock rings,
stomach growls when hungry, dog growls when
upset, hibernate when cold, grow toward the
sunlight, shiver when cold, laugh, sweat during a
test, make adrenaline when afraid…..
Grow, Develop and Die
 Growth indicates an increase in size, bigger
organisms and/or bigger cells – could be more
cells
 Development refers to changes in structure and
function.
Baby -> toddler -> teen -> adult -> elderly.
Also changes such as metamorphosis
 Senescence means to age.
 Living = mortal, won’t live forever. Even things
with long life spans (redwood tree 800 -2000
years, still eventually die)
Highly Organized
 Adult human has +30 trillion cells
 They aren’t just in a pile, and you wouldn’t work
well as one big 120 pound cell!
 Cells are highly organized internally by cell
membrane, organelles, DNA , etc.
 Organisms are also highly organized with cells
 tissues  organs  organ systems and then
organisms
 Unicellular organisms are also highly organized.
Homeostasis
Process of maintaining a steady internal
state while the external environment
changes
Body temp, blood glucose level, hydration,
etc.
Requires a constant input of energy.
1000 Cal a day to stay alive of the 20002500 need by an adult human.
Have DNA for Reproduction
 Cells wear out and need to be replaced
 Skin cells reproduce, asexually, to make more
skin cells
 Asexual means one source of DNA (one parent);
one skin cell divides and there are 2 new skin cells
 Organisms will grow develop and die – have to
make next generation or their species will be
extinct
 Reproduce more individuals by asexual
reproduction or make reproductive cells to be
used in sexual reproduction (potential new
organisms… not every acorn will be a tree)
Have DNA to Evolve
(sometimes called Adapt)
 The gene pool of a population changes over
long periods of time. (7-10 generations)
 This is genetic, not nervous, endocrine, etc.
 This is much slower and longer lasting than ‘responses’
 Incorporated into the structure of DNA is its
amazing ability to be replicated accurately AND
the ability to change and to pass on the new
version to the next generation.
 Process driven by Natural Selection
(if you have genes for more successful traits – at that
time, in that setting, then you will have offspring that will
be successful at leaving offspring. If environment
changes then “successful” traits will also change)