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The Study of Life
Chapter 1
Bio logy
Biology is the branch of science that studies living things
What is “life?”
How do scientists study it?
vs. Non-living
When talking about the qualities of “living things,” we are
often talking about the species level rather than the
individual level. “Skunks are living things,” rather than, “That
skunk is living, the one on the road is dead.”
• Observe the items in
the green trays.
Discuss with others:
• Is it alive? How do
we know?
• At what level of
organization should
this item be placed?
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 Laws and Theories are
products of scientific inquiry.
Scientific Evidence
• Based on _______
• Uniform in time and
• Perceived similarly by
many people.
• ________,
Forming Hypotheses
• Scientific Inquiry is often used to test
• A hypothesis is a
____________________ for an
• A valid hypothesis must be __________,
____________, and
• 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
• 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.”
• A hypothesis is testable if involves
specific variables in the real, physical
world that can be measured directly or
• 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
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.”
Testing Hypotheses
• Scientific inquiry is used to test
• Scientific inquiry can be carried out by:
• Experiments
• Observational studies
• Scientists design
experiments when their
questions ask, “What is
the natural cause of
what I am seeing?”
• Variables must be
Results must be
___________ to be
• Experiments use
controls and replication.
“Does this fertilizer cause
crops to mature faster?”
“Does pond water pH
affect Daphnia survival?”
are one type of
test variables
to try to find
the cause of
natural events.
Observational Studies
• Scientists design
observational studies when
their questions ask, “What
is happening here?”
• Observational studies may
be needed to establish
which variables to test in
an experiment.
“What lived here long
• In some fields, observation
may be all that is possible.
“What lives here now?”
Much of Astronomy and Paleontology involves
observational science. We can’t do experiments on
things out in space or that went extinct long ago.
Laws and Theories
• In general:
• Scientific Laws and Theories are both
products of Scientific Inquiry.
• Laws tend to be _____________ of
natural phenomena in given
• Theories tend to be _____________ of
how natural phenomena work.
Two misconceptions to avoid!
• Laws are NOT ideas or theories that are
“proven.” They are NOT “better” than
• Theories are NOT guesses that have not
been “proven” yet. Scientists to NOT
form theories and then “desperately” try
to “prove” them!
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
Describe patterns of
inheritance in terms of
Darwin’s Theory of
Natural Selection:
Explains why inherited
traits change in
populations over
A Unifying Theory
The gene pool of populations changes
over time. Changing environmental
conditions favor different gene
combinations at different times.
• Change in the genetics of a population
from generation to generation is called
• Evolution explains species diversity and
underlies all of modern Biology.
Modern evolutionary theory explains why organisms are
so diverse, yet all are related.
Three processes underlie evolution: genetic variability,
inheritance, and selection.
Genetic variability in
populations is normal.
Genetic variation is inherited when DNA is passed from
one generation to the next. Our DNA contains the code
for all of our inheritable traits.
Natural Selection,
one mechanism that
causes evolution, is a
tendency for genes
for traits that help an
organism survive and
reproduce to be
passed on from
generation to
generation. Traits that
interfere with
reproductive success
tend not to be passed
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
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
environment, such
as maintaining
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.
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.”
Life can be studied on many
different levels.
What is the smallest
level of organization
that meets our
criteria for “living
• The classification systems described are
applied to living organisms.
• Some particles are “proto-living” – having
a few of the characteristics of living
things, but not quite alive.
HIV Virus
• A virus has:
• _______________
• _______________
• A virus lacks a
metabolism and
cannot reproduce on
its own.
• Much, much smaller
than bacteria.
Viruses infecting a bacteria cell.
• A viroid is only
often in a ring.
• Viroids can,
however, act as
infectious agents.
Several plant
diseases are
caused by viroids.
• Prions are ____
___ that cause disease
(such as “mad cow”
• How prions replicate is
still not fully understood.
• Living things are complex, organized, and
maintain homeostasis.
• Scientists study living things using scientific
inquiry to make observations and test
• Laws and theories are the products of
• Evolution is the unifying theory of modern