The Characteristics of Life
AP Biology
Notes: #1
Life’s Diversity & Unity
Life has extensive diversity.
Despite its diversity, all living things are
composed of the same chemical elements
that make-up non-living things.
Yet, all living things have fundamental
characteristics that they share and help
distinguish from non-living things.
The Characteristics of Life
Biologists have devised a list of 8
characteristics that all life shares.
Something can be considered alive ONLY if it
displays ALL 8 of these characteristics.
Anything that possesses all 8 of the
characteristics of life is called an organism.
The 8 Characteristics of Life:
1.
Organization/Order – has cellular organization
(all organisms are made of 1 or more cells)
cell  tissue  organ  system  organism
Reproduces – DNA is the common genetic material
Growth & Development
Metabolism – acquires materials for energy
Responds to Stimuli – responds to the environment
Homeostasis/Regulation – maintains internal
balance
7. Evolutionary Adaptations – As a group, organisms
adapt and change over time.
8. Organic – Carbon is the basis of all biological
molecules found in living organisms
2.
3.
4.
5.
6.
The Characteristics of Life
1. Life has Cell(s) & is based on Cellular
Organization:
All life begins with the cell.
Cell = smallest unit of life.
In multi-cellular organisms, similar cells
cluster together to form tissues.
"Omnis cellula e cellula”
(Every cell out of a cell)
Rudolf Carl Virchow (1821 – 1902)
A Hierarchy of Biological
Organization
The hierarchy of life
– extends through many levels of biological
organization
The levels:
Atom  Molecule  Cell  Tissue 
Organ  System  Organism  Population
 Community  Ecosystem  Biosphere
Emergent Properties
Each new level of biological organization
has “emergent properties”.
Emergent Properties = features that result
due to interactions between parts
making up the whole that do not exist in
the parts alone.
“IN THE LIVING WORLD, THE WHOLE IS
INDEED MORE THAN THE SUM OF ITS
PARTS.”
The Characteristics of Life
2. Life reproduces:
All living organisms are able to produce
live offspring.
Life comes from life!
SPECIES = group
of organisms that
can breed &
produce fertile
Sexual
offspring
Asexual
DNA/Genes
All living
organisms contain
genetic
information that
can be passed on
through
generations.
Each offspring’s
DNA is unique!
3. Life Grows & Develops:
All living organisms grow & develop during
their life spans.
Growth: an increase in the
size or mass of an
organism due to an
increase in the size &
number of cells
Development: all of the
changes that take place
throughout the life span of
an organism
The Characteristics of Life
4. Life requires Energy/Metabolism:
Life acquires, stores, & processes nutrient
molecules from “food” for energy.
 PRODUCERS: most plants &
some unicellular organisms use
solar energy to make their own
food & fuel their activities.
 CONSUMERS: organisms that cannot
make their own food get energy by
consuming other organisms.
What is Metabolism?
All chemical reactions in the cell that make
parts or products from nutrient molecules
to utilize or create energy.
Two Types:
– Anabolism = synthesis reactions (to produce
& store energy)
– Catabolism = breaking down reactions (to
release energy)
“Here Comes the Sun…”
ULTIMATE SOURCE OF ENERGY = SUN!
Photosynthesis = process of transforming
solar energy into chemical energy stored in the
chemical bonds between organic nutrient
molecules
Cellular Respiration = process of acquiring
energy by metabolizing nutrient molecules
produced by photosynthesis
Byproducts of each support the other!
The Characteristics of Life
5. Life Responds to Stimuli:
Living things have the ability to react
(or respond) to an environmental
condition or stimulus.
Physiological or Behavioral Response
– often results in movement
Necessary to help ensure survival of
the organism & help it to carry out
daily activities or behaviors.
What is Stimuli?
Stimulus = anything in the
internal or external
environment that causes a
response
Response = reaction to a
stimulus; can be a
behavior change or
physical and/or chemical
response
Venus flytrap
The Characteristics of Life
6. Maintains Homeostasis:
All living organisms are able to
maintain a relatively constant internal
environment or condition.
Homeostasis: the regulation of an
organism’s internal environment within
certain boundaries to maintain
conditions suitable for life.
Organisms maintain homeostasis
by depending on:
Behavior
Innate Control Mechanisms
– Release of Enzymes, Hormones, Nerve
Impulses, etc.
– Positive & Negative Feedback Mechanisms
are Essential for Internal Regulation:
Organisms maintain dynamic balance by “switching
on & off” physiological pathways
Pathways can create products that stimulate new
pathways or even shut themselves “off.”
The Characteristics of Life
7. Life Adapts and Evolves:
Living things must adapt to their environment
to survive.
If a “trait” is advantageous,
– it becomes an adaptation.
– it can help some individuals survive
– it is passed on to future generations.
OVER LOTS OF TIME,
– the population’s genes can change/evolve
– because more individuals have the adaptation.
Adaptation = an
inherited trait that
gives an advantage
to organisms in their
environment & is
passed on
Evolution = changes in
the genetic make-up
of an organism over
time
Evolution occurs by natural selection of
adaptations.
Clarifying Evolution, Adaption, and
Natural Selection
Evolution = the theory on how changes in a
population (i.e. group of interbreeding species)
occurs over extended time
– assumes that the “how” or mechanism by which
adaptations occur in a species is natural selection
Natural Selection = the mechanism by which
evolutionary adaptations occur over time in
response to a population’s environment
Adaptation = the product of natural selection; a
trait or physical modification that makes organisms
better suited for their environment
Evolutionary View on Life
Began in 1859 when Charles Darwin
published On the Origin of Species by
Natural Selection
Origin of Species
Highlighted:
– Natural Selection
– Descent with Modification
Figure 1.18
When Natural Selection Occurs
A population’s have heritable variations or
traits.
– exposed to the environment all the time.
Selection occurs when traits in a
population give an organism an advantage
for survival and successful reproduction.
– Thus, selection is when heritable variations
favor the reproductive success of some
individuals over others.
Products of Natural Selection
Are exquisite adaptations of organisms to
the special circumstances of their way of
life and their environment
Evolution Supports the Theme of
“Descent with Modification”
“Descent with Modification” explains
why life has both unity and diversity.
– UNITY: All organisms share common
defining features of life, suggesting they
“descended” from a common ancestor
– DIVERSITY: The process of evolution
allows species to modify features in order
to adapt to different ways of life. This
allows for life to be diverse.
The Characteristics of Life
8. Life is ORGANIC:
Living organisms are made of
molecules with lots of Carbon atoms!
Carbon…the “stuff” of life
Organic molecules contain a variety of atomic
elements.
– i.e. hydrogen, oxygen, nitrogen, phosphorus, & sulfur
Yet, carbon atoms are the most predominant
structures in organic molecules
– typically linked as carbon-to-carbon bonds
All cells share a common set of carbon-containing
molecules (called “organic molecules”) dissolved
or dispersed in H20 as a common medium of
housing and interaction.