Chapter 1
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 Key Concepts

1.1 Living Organisms Share Common Aspects of Structure,
Function, and Energy Flow

1.2 Life Depends on Organization and Energy

1.3 Genetic Systems Control the Flow, Exchange, Storage,
and Use of Information

1.4 Evolution Explains the Diversity as Well as the Unity of
Life

1.5 Science Is Based on Quantitative Observations,
Experiments, and Reasoning
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 Biology: the scientific study of
living things or organisms.
 Living things are all descended
from a single-celled ancestor (a
single common ancestor).
 The characteristics shared by all
organisms logically lead to the
conclusion that all life has a
common ancestry.
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 Characteristics shared by all living organisms:
• Composed of a common set of chemical components and similar
structures (e.g., cells)
• Depend on interactions among structurally complex parts to
maintain the living state
 Contain genetic information that uses a nearly universal code
 Convert molecules obtained from their environment into new
biological molecules
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• Extract energy from the environment and use it for life functions
• Replicate their genetic information in the same manner when
reproducing
 Share structural similarities among a fundamental set of genes
 Evolve through gradual changes in genetic information
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 Earth formed between 4.6 and 4.5 billion years ago.
 The earliest life evolved about 600 million years later.
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Figure 1.1 Life’s Calendar
 Complex biological molecules
possibly arose from random
associations of chemicals in the
early environment.
 Experiments that simulate
conditions on early Earth show
that this was possible.
 Critical step for evolution of life:
 Formation of nucleic acids that
could reproduce themselves and
contain the information to produce
proteins.
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 The next step:
 Biological molecules were
enclosed in a membranes,
to form a cell.
 Fatty acids, which form
membrane-like films in
water, were important in
forming membranes.
 Membranes separate the
cell from the surrounding
environment.
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 For 2 billion years, organisms were unicellular prokaryotes.
 Early prokaryotes were confined to oceans, where they were
protected from UV light.
 There was little or no O2 in the atmosphere, and hence no
protective ozone (O3) layer.
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Figure 1.2 The Basic Unit of Life Is the Cell
 Photosynthesis evolved
about 2.7 billion years ago.
 The energy of sunlight is
transformed into the
chemical-bond energy of
biological molecules.
 Earliest photosynthetic cells
were probably similar to
cyanobacteria.
 O2 was a by-product of
photosynthesis, and it began
to accumulate in the
atmosphere.
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Figure 1.3 Photosynthetic Organisms Changed Earth’s Atmosphere
 O2 was poisonous to many
early prokaryotes.
 Organisms that could tolerate
O2 evolved aerobic
metabolism (energy
production using O2), which
is more efficient than
anaerobic metabolism.
 Organisms were able to grow
larger. Aerobic metabolism is
used by most living
organisms today.
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 O2 also produced a layer of ozone (O3) in the upper
atmosphere.
 This layer absorbs UV light, and its formation allowed
organisms to move from the ocean to land.
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 Some cells evolved membrane-
enclosed compartments called
organelles, where specialized
functions can be performed.
 The nucleus contains the genetic
information.
 These cells are called eukaryotes.
 Prokaryotes lack nuclei and other
internal compartments.
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 Some organelles may have originated by endosymbiosis,
when larger cells engulfed smaller ones.
 Mitochondria (sites of energy generation) probably evolved
from engulfed prokaryotic organisms.
 Chloroplasts (sites of photosynthesis) probably evolved from
engulfed photosynthetic prokaryotes.
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 Multicellular organisms arose
about 1 billion years ago.
Groups of eukaryote cells
probably failed to separate
after division.
 Cellular specialization—
cells became specialized to
perform certain functions.
 This allowed multicellular
eukaryotes to become larger
and adapt to specific
environments.
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 Evolution of species:
 Mutations (changes) are introduced when a genome is replicated.
 Some mutations give rise to structural and functional changes in
organisms, and new species arise.
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 Each species has a distinct
scientific name, a binomial:
• Genus name
• Species name
 Example: Homo sapiens
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 Evolutionary relationships of
species can be determined by
comparing genomes.
 Genome sequencing and other
molecular techniques have
added molecular evidence to
knowledge from the fossil
record.
 Phylogenetic trees document
and diagram evolutionary
relationships.
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Figure 1.4 The Tree of Life
 Relationships in the tree of life are based on fossil evidence,
structures, metabolic processes, behavior, and molecular
analyses.
 Three domains of life:
 Bacteria (prokaryotes)
 Archaea (prokaryotes)
 Eukarya (eukaryotes)
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 All organisms that are alive today descended from common
ancestors in the past.
 Living species did not evolve from other species living today.
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 Because all life is related, discoveries made using one type of
organism can be extended to other types.
 Biologists use model organisms for research, such as the
green alga Chlorella to study photosynthesis.
Bozeman Science – Essential
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Characteristics of Life
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 The second law of thermodynamics states that, left to
themselves, organized entities tend to become more random.
 Energy is required for cells to combat the tendency for their
molecules, structures, and systems to lose organization.
 Energy is required by cells throughout their lives.
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 Organization is apparent in
a hierarchy of levels from
molecules to ecosystems.
 Cells use energy to
synthesize complex
molecules by assembling
atoms into new, highly
organized configurations.
 Organization is essential for
cells to function in a
multicellular organism,
which has many levels of
organization.
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Figure 1.5 Life Consists of Organized Systems at a Hierarchy of Scales (1)
 Organisms also interact with their physical environment and
with each other, resulting in hierarchy in the larger biological
world.
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 A system is a set of interacting parts (components) in which
neither the parts nor the whole can be understood without
taking into account the interactions (processes).
 Systems are found at every level of biological organization.
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Figure 1.7 Organized Systems Exist at Many Levels
 Biological systems are dynamic:
 Characterized by rapid flows of matter and energy.
 They constantly exchange energy and matter with their
surroundings.
 But even though there is constant turnover of atoms, molecules,
etc., the organization of the systems persist.
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 Feedback: the amount of one component in a system affects the
rate of an earlier process in the system.
 Positive feedback occurs when a product of the system speeds
up an earlier process.
 Negative feedback occurs when a product of the system slows
down an earlier process.
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 Positive feedback tends to destabilize a system (sometimes
advantageous, provided it is ultimately brought under control).
 Negative feedback tends to stabilize systems and is very
common in regulatory systems.
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 Systems analysis is used to understand how biological
systems function.
 The system components are identified, and processes by which
the components interact are determined.
 Rates of interactions can be affected by feedback.
 Then we can analyze how the system will change through time.
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 Mathematical equations express amounts of the different
components and include processes and their rates, resulting in
a computational model.
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 If a computational model is
well grounded in factual
knowledge of the
biological system, it will
mimic the biological
system.
 Computational models can
be used for prediction, for
instance, the future
behavior of a system in a
warming world.
 Parameters of the model
are adjusted to take into
account the expected
increases in temperature.
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 The genome is the sum
total of all the
information encoded by
an organism’s genes.
 DNA consists of
repeating subunits
called nucleotides.
 A gene is a specific
segment of DNA that
contains information for
making one or more
proteins.
 Proteins govern
chemical reactions in
cells and form much of
an organism’s structure.
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 All cells in a multicellular organism contain the same genome,
but different cells have different functions.
 The different types of cells must express different parts of the
genome.
 How cells control genome expression is a major focus of
biological research.
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 Mutations alter nucleotide sequences of a gene, and the protein
is often altered as well.
 Mutations may occur during replication or be caused by
chemicals and radiation.
 Most are harmful or have no effect, but some may improve the
functioning of the organism.
 Mutations are the raw material of evolution.
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 Complete genome sequences have been determined for many
organisms.
 They are used to study the genetic basis of everything from
physical structure to inherited diseases and evolutionary
relationships.
 Bioinformatics is the field of study that developed to organize
and process the immense amount of data resulting from
genome sequencing.
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 Evolution is a change in genetic makeup of biological
populations through time—a major unifying principle of
biology.
 A common set of evolutionary mechanisms applies to all
organisms.
 The constant change that occurs among populations gives rise
to all the diversity of life.
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 Charles Darwin proposed that all
living organisms are descended
from a common ancestor by the
mechanism of natural selection.
 Natural selection leads to
adaptations—structural,
physiological, or behavioral traits
that enhance an organism’s
chances of survival and
reproduction.
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Figure 1.10 Adaptations to the Environment
 Two kinds of explanations for adaptations:
 Proximate explanations—immediate genetic, physiological,
neurological, and developmental processes that explain how an
adaption works.
 Ultimate explanations—what processes led to the evolution of an
adaptation.
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 In science, a theory is a body of scientific work in which
rigorously tested and well-established facts and principles are
used to make predictions about the natural world.
 Evolutionary theory is:
1. A body of knowledge supported by facts
2. The resulting understanding of processes by which populations
have changed and diversified over time, and continue to evolve
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 Evolution can be
observed and
measured by:
• Changes in genetic
composition of
populations over
short time frames
• The fossil record—
population changes
over very long time
frames
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 Scientific investigations are
based on observation,
experimentation, and
reasoning.
 Understanding the natural
history of organisms—how they
get food, reproduce, behave,
regulate functions, and interact
with other organisms—
facilitates observation and
leads to questions.
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 Observation is enhanced by technology—microscopes,
imaging, genome sequencing, satellites.
 Observations must be quantified by measurement and
mathematical and statistical calculations.
Bozeman Science – Scientific Method
Video
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 The scientific
method
(hypothesis–
prediction
method):
1.
2.
3.
4.
5.
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Observations
Questions
Hypotheses
Predictions
Testing
 To answer questions, biologists look at
what is already known to form possible
answers, or hypotheses.
 Predictions are made based on
observations, and experiments are
designed to test these predictions.
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 Controlled experiments
manipulate the factor, or
variable, that is predicted to
be causing the phenomenon
being investigated.
 A method is devised to
manipulate only that variable
in an “experimental” group,
which is compared with an
unmanipulated “control”
group.
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Figure 1.12 Controlled Experiments Manipulate a Variable (Part 1)
Figure 1.12 Controlled Experiments Manipulate a Variable (Part 2)
 Independent variable—the variable being manipulated
 Dependent variable—the response that is measured
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 Comparative experiments look for differences between
samples or groups.
 The variables cannot be controlled; data are gathered from different
sample groups and compared.
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Figure 1.13 Comparative Experiments Look for Differences among Groups (Part 1)
Figure 1.13 Comparative Experiments Look for Differences among Groups (Part 2)
 Statistical methods help scientists determine if differences
between groups are significant.
 Statistical tests start with a null hypothesis—that no
differences exists.
 Statistical methods eliminate the possibility that results are due
to random variation.
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 Not all forms of inquiry into nature are scientific.
 Scientific hypotheses must be testable and have the potential of
being rejected.
 Science depends on evidence that comes from reproducible
and quantifiable observations.
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 Religious or spiritual explanations of natural phenomena are
not testable and therefore are not science.
 Science does not say that untestable religious beliefs are
necessarily wrong, just that they cannot be addressed using
scientific methods.
 Many advances in science raise ethical concerns. Science can
not tell us how we should address these concerns.
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