The Study of Life
Chapter 1
What is Life?
• The concept of “living” can be difficult to
define, since many qualities of living
things can be seen in non-living things:
• Crystals (non-living) can grow.
• A thermostat (non-living) responds to
the environment.
Qualities of Living Things
• Living things:
• are complex, organized, and made up of cells.
• maintain homeostasis.
• respond to stimuli.
• reproduce and grow.
• use materials and energy.
• as species, adapt and evolve.
Complex and organized
All living things
have DNA, which
contains
information to
build cell parts.
Cells are the basic
unit of living things.
Organisms can be single-celled,
or cells can organize into tissues
and organs.
Maintain Homeostasis
Living organisms
need to maintain an
internal
environment, such
as maintaining
temperature.
Respond to stimuli
All living things have ways of
sensing the environment that allow
them to respond to threats and find
food or favorable environments.
Reproduce and grow
Living things produce more
of their kind through
reproduction. The young
grow to maturity and the
cycle begins again.
Use materials and energy
In order to maintain complexity, maintain homeostasis,
to grow, and to respond to the environment,
organisms must take in energy and materials. Living
things have a metabolism and give off waste products
as they use materials.
Which of these are characteristics of living
organisms?
90%
1. Responds to stimuli.
2. Maintains
homeostasis.
3. Has an organized
structure.
4. Only 1 and 3
5. All of these
5%
0%
1
2
2%
3
3%
4
5
Still a relevant question
“What is life?” isn’t just a
question that you left
behind in Kindergarten.
Astrobiologists who search
for signs of life on other
planets look for many of
the same characteristics of
terrestrial life.
Microbiologists studying
nanobacteria may
challenge our current
understanding of “life.”
Scientific Inquiry
• Science is an investigation of the natural
world, using evidence from nature to
support explanations.
• The methods used by scientists to
investigate the natural world are called
Scientific Inquiry.
• Scientific Laws and Theories are
products of scientific inquiry.
Hypothesis Testing
• Scientific Inquiry is often used to test
hypotheses.
• A hypothesis is a tentative explanation
for an observation.
• A valid hypothesis must be specific,
testable, and falsifiable.
Scientific Evidence
• Based on natural
causes.
• Uniform in time and
space.
• Perceived similarly by
many people.
• Objective, measurable.
Forming Hypotheses
• Scientific Inquiry is often used to test
hypotheses.
• A hypothesis is a tentative explanation
for an observation.
• A valid hypothesis must be specific,
testable, and falsifiable.
Specific
• A hypothesis is specific if it
addresses particular observations
and has specific variables.
• Not specific: “Toxins in water make
fish populations decline.”
• Specific: “The herbicide glyphosate
causes trout embryos to die in the
egg when present in water at
levels of 100 parts per million or
more.”
Falsifiable
• A hypothesis is falsifiable if it can
be “true or false,” either supported
or rejected by evidence. Note we do
not say “proven” or “disproven.”
• Not falsifiable: “Black licorice is the
best kind of licorice.” (Opinions
cannot be true or false.)
• Falsifiable: “Over half of WOU
students in our biology class prefer
black licorice over red.”
Let’s test it!
Which kind of licorice
do you prefer?
33%
33%
33%
1. Black licorice
2. Red licorice
3. No preference
1
2
3
Testable
• A hypothesis is testable if involves
specific variables in the real, physical
world that can be measured directly or
indirectly.
• Not testable: “Students do poorly on
exams because of bad luck.”
• Testable: “Biology students who make
outlines and concept maps while
studying their textbook score 10% better
on exams than students who only read
the textbook.”
A hypothesis does not…
• …have to be “true” at the start of the
experiment. We don’t know until the
experiment is over whether the
hypothesis is supported or not.
• …have to explain everything. It only has
to address one variable at a time. If you
try to write a hypothesis that explains
everything, it is no longer specific.
Hypotheses often begin with an observation that leads
to questions.
Questions invite possible explanations.
These possible explanations are hypotheses. To be
valid, a hypothesis must be specific, testable, and
falsifiable – but it doesn’t have to be correct! In fact,
you don’t know if it is correct or not until you test it.
Each possible explanation — hypothesis — can give rise
to a prediction, often stated in an IF...THEN format.
A good prediction suggests a procedure that can test the
hypothesis.
Scientists test hypotheses and accept or reject
hypotheses based on data. They do not set out to prove
hypotheses or they may bias their results.
Once the procedures are carried out, scientists use the
data to reach a conclusion regarding the hypothesis.
Notice that the hypothesis is supported rather
than “proven.”
Observation
• What’s happening in this
picture?
Question
Hypothesis
Prediction
Experiment or
Observation
Conclusion
• Write an IF – THEN hypothesis
and prediction based on the
picture.
W
O
R
K
T
O
G
E
T
H
E
R
Experiments
are one type of
scientific
inquiry.
Experiments
test variables
to try to find
the cause of
natural events.
Observational studies are also part of scientific inquiry.
Much of Astronomy and Paleontology, for example,
involves observational science.
In order to test a hypothesis, a
scientist must conduct:
33%
33%
33%
1. An experiment.
2. An observation.
3. A study, using an
appropriate type of
inquiry for the
hypothesis.
1
2
3
Laws and Theories
• In general:
• Scientific Laws and Theories are both
products of Scientific Inquiry.
• Laws tend to be descriptions of natural
phenomena in given circumstances.
• Theories tend to be explanations of
how natural phenomena work.
Law of Gravity
describes what
happens when you
drop a rock or launch a
rocket at the moon.
Gravitational Theory explains
why dropped objects fall
toward the center of the mass
of the Earth.
Mendel’s Laws of
Heredity:
Describe patterns of
inheritance in terms of
probability.
Darwin’s Theory of
Natural Selection:
Explains why inherited
traits change in
populations over
generations.
A scientific explanation based on many observations
that have been tested and supported by many
scientists is a:
33%
33%
33%
1. Law
2. Theory
3. Hypothesis
1
2
3
Scientific laws are:
33%
33%
33%
1. Proven theories.
2. Proven hypotheses.
3. Descriptions of
natural phenomena.
1
2
3
Recap
• Living things are complex, organized, and
maintain homeostasis.
• Scientists study living things using scientific
inquiry to make observations and test
hypotheses.
• Laws and theories are the products of
science.
• Evolution is the unifying theory of modern
biology.