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The Scientific Study of Life
Chapter 1
BIOL114
Dave Werner
1.1 What is Life?
 We understand life by thinking about nature at
different levels of organization
 Nature’s organization begins at the level of
atoms, and extends through the biosphere
 The quality of life emerges at the level of the cell
Making Sense of the World
 Nature is everything in the universe except what
humans have manufactured
A Pattern in Life’s Organization
 Atoms
• Fundamental building blocks of all substances
 Molecules
• Consisting of two or more atoms
 Cell
• The smallest unit of life
 Organism
• An individual consisting of one or more cells
A Pattern in Life’s Organization
 Population
• Individuals of the same species in the same area
 Community
• Populations of all species in the same area
 Ecosystem
• A community and its environment
 Biosphere
• All regions of the Earth where organisms live
Levels of Organization in Nature
Levels of Organization in Nature
Emergent Properties
 Each level of organization in nature has
emergent properties – a characteristic of a
system that does not appear in any of its
component parts
Overview of Life’s Unity
 All living things have similar characteristics
• Continual inputs of energy and the cycling of
materials maintain life’s complex organization
• Organisms sense and respond to change
• DNA inherited from parents is the basis of growth
and reproduction in all organisms
Energy and Life’s Organization
 Energy
• The capacity to do work
 Nutrients
• Atoms or molecules essential in growth and
survival that an organism cannot make for itself
Producers and Consumers
 Producers
• Acquire energy and raw materials from the
environment
• Make their own food (photosynthesis)
 Consumers
• Cannot make their own food
• Get energy by eating producers and other
organisms
Homeostasis
 Homeostasis
• Organisms use receptors to help keep conditions
in their internal environment within ranges that
their cells can tolerate
Organisms Grow and Reproduce
 Organisms grow, develop, and reproduce
using information in their DNA, a nucleic acid
inherited from parents
 Information encoded in DNA is the source of an
individual’s distinct features (traits)
Same Materials, Many Products
 20 amino acids are the building blocks used to
build a great variety of proteins
Instructions in DNA Guide Development
Life’s Underlying Unity
 All organisms consist of one or more cells, which
stay alive through ongoing inputs of energy and
raw materials
 All sense and respond to change; all inherited
DNA, a type of molecule that encodes
information necessary for growth, development,
and reproduction
Animation: One-way energy flow and
materials cycling
Overview of Life’s Diversity
 Of an estimated 100 billion kinds of organisms
that have ever lived on Earth, as many as 100
million are with us today
1.2 The Tree of Life Includes Three Main
Branches
 Scientific Naming - Each type of organism is
given a two-part name that includes genus and
species names
 Genus
• A group of species that share unique features
 Species
• Individuals that share one or more heritable traits
and can interbreed (if sexually reproducing)
Scientific Naming
 The heavy-beaked parrotfish, Scarus gibbus
Classification Systems
 Classification systems group species by their
shared, heritable traits
 All organisms are classified into three domains
• Bacteria, archaea, and eukaryotes
• Eukaryotes include plants, animals, protists
and fungi
Comparison of Life’s Three Domains
Diversity of Life
Diversity of Life
Life’s Diversity
 Many millions of kinds of organisms, or species,
have appeared and disappeared over time
 Each kind is unique in some aspects of its body
form or behavior
Animation: Life’s diversity
One-Way Flow of Energy and Cycling of
Materials through an Ecosystem
energy input,
mainly from
sunlight
PRODUCERS
plants and other
self-feeding organisms
nutrient
cycling
CONSUMERS
animals, most fungi,
many protists, bacteria
A Energy inputs from
the environment flow
through producers,
then consumers.
B Nutrients become
incorporated into the
cells of producers
and consumers.
Some nutrients
released by
decomposition cycle
back to producers.
C All energy that
enters an ecosystem
eventually flows out
of it, mainly as heat.
energy output, mainly heat
Fig. 1-3, p. 6
energy input,
mainly from
sunlight
PRODUCERS
plants and other
self-feeding organisms
nutrient
cycling
CONSUMERS
animals, most fungi,
many protists, bacteria
energy output, mainly heat
A Energy inputs from
the environment flow
through producers,
then consumers.
B Nutrients become
incorporated into the
cells of producers
and consumers.
Some nutrients
released by
decomposition cycle
back to producers.
C All energy that
enters an ecosystem
eventually flows out
of it, mainly as heat.
Stepped Art
Fig. 1-3, p. 6
An Evolutionary View of Diversity
 A theory of evolution by natural selection is an
explanation of life’s diversity
Variation and Mutation
 Information encoded in DNA is the basis of traits
an organism shares with others of its species
 Mutations are the original source of variation in
traits
Adaptation
 Some forms of traits are more adaptive than
others, so their bearers are more likely to survive
and reproduce
 Over generations, adaptive traits tend to
become more common in a population; less
adaptive forms of traits become less common or
are lost
Evolution and Natural Selection
 Evolution is change in a line of descent
• Traits that characterize a species can change
over generations in evolving populations
 Natural selection is an evolutionary process
• Differential survival and reproduction among
individuals that vary in the details of their shared,
heritable traits
Artificial and Natural Selection
1.3 Key Concepts:
Explaining Unity in Diversity
 Theories of evolution, especially a theory of
evolution by natural selection, help explain why
life shows both unity and diversity
 Evolutionary theories guide research in all fields
of biology
1.5 Critical Thinking and Science
 Critical thinking is judging the quality of
information
 Science is limited to that which is observed
• Helps minimize bias in judgments by focusing on
testable ideas about observable aspects of nature
A Guide to Critical Thinking
1.6 How Science Works
 Scientists make and test potentially falsifiable
predictions about how the natural world works
Observations, Hypotheses, and Tests
 Researchers make observations, form
hypotheses (testable assumptions), and make
predictions about what might occur if the
hypothesis is correct
A Scientific Approach
Research in Laboratory and Field
About the Word “Theory”
 A hypothesis that is inconsistent with results of
scientific tests (evidence) is modified or
discarded
 A scientific theory is a long-standing
hypothesis that is used to make useful
predictions
Examples of Scientific Theories
Some Terms Used in Experiments
 Experiments
• Tests that can support or falsify a prediction
 Variable
• A single characteristic in a set of individuals that
differs from the control group in an experiment
Some Terms Used in Experiments
 Experimental group
• Group with a single variable characteristic to be
tested against a control group in an experiment
 Control group
• Group identical to the control group, except for
the variable
1.7 The Power of Experimental Tests
 Researchers unravel cause and effect in
complex natural processes by studying the
effects of one variable at a time
Potato Chips and Stomach Aches
 Researchers tested the prediction that Olestra®
in potato chips causes cramps
• Experimental group: Olestra chips
• Control group: regular chips
Experiment:
Olestra and Stomach Cramps
Hypothesis
Olestra® causes intestinal cramps.
Prediction
People who eat potato chips made with Olestra will be more
likely to get intestinal cramps than those who eat potato
chips made without Olestra
Experiment
Control Group
Eats regular
potato chips
Experimental Group
Eats Olestra
potato chips
Results
Control Group
Eats regular
potato chips
Experimental Group
Eats Olestra
potato chips
Conclusion
Percentages are about equal. People who eat potato chips
made with Olestra are just as likely to get intestinal cramps
as those who eat potato chips made without Olestra.
These results do not support the hypothesis.
Stepped Art
Fig. 1-10, p. 14
Butterflies and Birds
 Why does the peacock butterfly flick its wings
when birds are near?
 Researchers tested two hypotheses
• Wing spots deter predatory birds
• Hissing and clicking sounds deter predatory birds
Peacock Butterfly Defenses
against Predatory Birds
Fig. 1-11a, p. 15
Fig. 1-11b, p. 15
Fig. 1-11c, p. 15
Results: Peacock Butterfly Experiment
Asking Useful Questions
 Scientists try to design single-variable
experiments that yield quantitative results
 When studying humans, isolating a single
variable is not often possible
1.8 Sampling Error in Experiments
 Researchers experiment on subsets of a group
• Results may differ from results of the same
experiment performed on the whole group
 Sampling error is a difference between results
from a subset and results from the whole
• Small sample size increases the likelihood of
sampling error in experiments
Animation: Sampling error
Summary of Life’s Characteristics
1.5-1.8 Key Concepts:
How We Know
 Biologists make systematic observations,
predictions, and tests in the laboratory and in the
field
 They report their results so others may repeat
their work and check their reasoning
Animation: Insect development
Animation: Three domains
Video: Finding new species