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The Science of Biology
Chapter 1
1
2
The Science of Life
• Biology unifies much of natural science
• Life defies simple definition
– Living systems are the most complex chemical systems on Earth
– Life is constrained by the properties of chemistry and physics
• Science is becoming more interdisciplinary
– Combining multiple fields
3
• 7 characteristics of all living organisms
1. Cellular organization
2. Ordered complexity
3. Sensitivity
4. Growth, development, and reproduction
5. Energy utilization
6. Homeostasis
7. Evolutionary adaptation
• Living systems show hierarchical
organization
– Cellular level
• Atoms, molecules, organelles, cells
• Cell is the basic unit of life
– Organismal level
• Tissues, organs, organ systems
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5
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Atoms Molecule Macromolecule
CELLULAR LEVEL
Organelle Cell
0.2 µm
O
C
H
N
O
H
NC
O
(organelle): © Dr. Donald Fawcett & Porter/Visuals Unlimited; (cell): © Steve Gschmeissner/Getty Images
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Tissue Organ
100 µm
ORGANISMAL LEVEL
Organ system Organism
(tissue): © Ed Reschke; (organism): © Russell Illig/Getty Images RF
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
– Populational level
• Population, community
– Ecosystem level
– Biosphere
• Earth is an ecosystem we call the biosphere
• Each level has emergent properties
– Result from interaction of components
– Cannot be deduced by looking at parts
themselves
– “Life” is an emergent property
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8
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
POPULATIONAL LEVEL
Population Species Community Ecosystem Biosphere
(population): © George Ostertag/agefotostock; (species): © PhotoDisc/Volume 44 RF; (community): © Ryan McGinnis/Alamy;
(ecosystem): © Robert and Jean Pollock; (biosphere): NASA
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The Nature of Science
• Science aims to understand the natural
world through observation and reasoning
• Science begins with observations,
therefore, much of science is purely
descriptive
– Classification of all life on Earth
– Human genome sequencing
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• Science uses both deductive and inductive
reasoning
• Deductive reasoning uses general
principles to make specific predictions
• Inductive reasoning uses specific
observations to develop general
conclusions
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• Scientists use a systematic approach to gain understanding of the natural world
– Observation
– Hypothesis formation
– Prediction
– Experimentation
– Conclusion
12
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Observation
Question
Potential
hypotheses
Remaining
possible
hypotheses
Last remaining
possible
hypothesis
Hypothesis 1
Hypothesis 2
Hypothesis 3
Hypothesis 4
Hypothesis 5
Hypothesis 2
Hypothesis 3
Hypothesis 5
Hypothesis 5
Reject
hypotheses
1 and 4Experiment
Reject
hypotheses
2 and 3
Experiment
Modify hypothesis
Experiment 4Experiment 1
Predictions
Experiment 2 Experiment 3
Predictions
confirmed
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• A hypothesis is a possible explanation for
an observation
• A hypothesis
– Must be tested to determine its validity
– Is often tested in many different ways
– Allows for predictions to be made
• Iterative
– Hypotheses can be changed and refined with
new data
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• Experiment
– Tests the hypothesis
– Must be carefully designed to test only one
variable at a time
– Consists of a test experiment and a control
experiment
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• Predictions
– Hypotheses should make predictions
– Predictions provide a way to test the validity of
hypotheses
– Hypothesis must be rejected if the experiment
produces results inconsistent with the
predictions
– The more experimentally supported
predictions a hypothesis makes, the more
valid the hypothesis
16
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
SCIENTIFIC THINKING
Test: Use swan-necked flasks to prevent entry of microorganisms. To
ensure that broth can still support life, break swan-neck after sterilization.
Question:
Broken
neck
of flask
Flask is sterilized
by boiling the broth.
Unbroken flask
remains sterile.
Broken flask becomes
contaminated after
exposure to germ-laden air.
Conclusion: Growth in broth is of preexisting microorganisms.
What is the source of contamination that occurs in a flask of nutrient
broth left exposed to the air?
Germ Hypothesis: Preexisting microorganisms present in the air contaminate
nutrient broth.
Prediction: Sterilized broth will remain sterile if microorganisms are prevented
from entering flask.
Spontaneous Generation Hypothesis: Living organisms will spontaneously
generate from nonliving organic molecules in broth.
Prediction: Organisms will spontaneously generate from organic molecules
in broth after sterilization.
Result: No growth occurs in sterile swan-necked flasks. When the neck is
broken off, and the broth is exposed to air, growth occurs.
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• Philosophical approaches to science
– Reductionism
• To break a complex process down to its simpler
parts
– Systems biology
• Focus on emergent properties that can’t be
understood by looking at simpler parts
• Models in science
– Way to organize thought
– Parts provided by reductionist approach
– Model shows how they fit together
– Suggest experiments to test the model
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• Scientific theory
– Is a body of interconnected concepts
– Is supported by much experimental evidence
and scientific reasoning
– Expresses ideas of which we are most certain
• Compare to general meaning of theory
– Implies a lack of knowledge or a guess
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Darwin and Evolution
• Example of how a scientist develops a
hypothesis and a theory gains acceptance
• Charles Darwin served as naturalist on
mapping expedition around coastal South
America
• 30 years of observation and study before
publishing On the Origin of Species by
Means of Natural Selection
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Voyage of the HMS BeagleCopyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
NORTH
PACIFIC
OCEAN
Marquesas
Society
Islands
Straits of Magellan
Cape Horn Tierra del Fuego
SOUTH
ATLANTIC
OCEAN
New
Zealand
Hobart
King George’s
Sound
Mauritius
Bourbon Island
NORTH
PACIFIC
OCEANPhilippine
Islands
British Isles
Western
IslesEUROPE ASIA
Madagascar
Friendly
Islands
Equator
NORTH
AMERICA
Galápagos
Islands
NORTH
ATLANTIC
OCEAN
Cape Verde
Islands
Canary
Islands
AFRICA
Sydney
AUSTRALIA
INDIAN
OCEAN
Cape of
Good Hope
Falkland
Islands
Valparaiso
SOUTH
AMERICA
Port DesireBuenos Aires
Montevideo
Keeling
Islands
Bahia
Ascension
St. Helena
Rio de Janeiro
• Darwin was not the first to propose
evolution
– Living things have changed over time
• Darwin’s contribution was a mechanism
– Natural selection
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• On the Beagle, Darwin saw that
characteristics of similar species varied
from place to place
• Galápagos Finches
– 14 related species differ only slightly
– “Descent with modification” or evolution
23
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Woodpecker Finch (Cactospiza pallida) Large Ground Finch (Geospiza magnirostris) Cactus Finch (Geospiza scandens)
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• Darwin studied Thomas Malthus’s An
Essay on the Principle of Population
– Populations of plants and animals increase
geometrically
– Humans can only increase their food supply
arithmetically
– Populations of species remain constant
because death limits population numbers
• Darwin saw that
although every
organism has
the potential to
produce more
offspring, only a
limited number
do survive and
reproduce
themselves
25
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2
6
18
54
46
8
geometric progression
arithmetic progression
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• Evidence supporting Darwin’s theory has
only grown
– Fossil record
• Transitional forms have been found at predicted
positions in time
– Earth’s age
• Physicists of Darwin’s time were wrong
• Earth is very old – 4.5 billion years old
– Mechanism for heredity
• Mendel’s laws of inheritance were unknown to
Darwin
– Comparative anatomy
• Vertebrate forelimbs all share the same basic array
of bones
• Homologous – same evolutionary origin but now
differ in structure and function
• Analogous – structures of different origin used for
the same purpose (butterfly and bird wings)
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28
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Human Cat Porpoise HorseBat
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– Molecular Evidence
• Compare genomes or proteins of different organisms
• Phylogenetic trees –based on tracing origin of particular nucleotide changes to reconstruct an evolutionary history
Human Rhesus Dog FrogBird
Number of Amino Acid Differences in a Hemoglobin Polypeptide
10 20 30 70600 40 50
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Unifying Themes in Biology
• Cell theory
– All organisms composed of cells
– Cells are life’s basic units
– All cells come from preexisting cells
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a.
b.
60 µm
500 µm
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
a: © Dennis Kunkel/Phototake; b: © Karl E. Deckart/Phototake
• Molecular basis of inheritance
– Deoxyribonucleic acid (DNA)
– Sequence of 4 nucleotides encode cell’s
information
– Gene – discrete unit of information
– Genome – entire set of DNA instructions
– Continuity of life depends on faithful copying
of DNA into daughter cells
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• Structure and function
– Study structure to learn function
– Know a function – look for that structure in
other organisms
– Example
• Receptor on human cell for insulin known
• Find similar molecule in a worm
• Might conclude this molecule functions the same in
the worm
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• Diversity of life arises by evolution
– Underlying unity of biochemistry and genetics
argues for life from the same origin event
– Diversity due to evolutionary change over
time
– 3 domains
• Bacteria – single-celled prokaryote
• Archaea – single-celled prokaryote
• Eukarya – single-celled or multicellular eukaryote
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Eukarya
Plantae
Fungi
Animalia
Protista
(plantae middle): © David M. Dennis/Animals Animals; (plantae right): © Corbis/Volume 46 RF; (fungi left): © Royalty Free/Corbis; (fungi middle):
© Mediscan/Corbis; (fungi right): © PhotoDisc BS/Volume 15 RF; (animalia left): © Royalty-Free/Corbis; (animalia middle): © Tom Brakefield/Corbis;
(animalia right): © PhotoDisc/Volume 44 RF; (protista left): © Corbis/Volume 64 RF; (protista middle): © Tom Adams/Visuals Unlimited;
(protista right): © Douglas P. Wilson/Frank Lane Picture Agency/Corbis
• Evolutionary conservation
– All organisms today descended from a simple
creature 3.5 BYA
– Some characteristics preserved – use of DNA
– Conservation reflects that they have a
fundamental role
35
• Cells are information-processing systems
– Information in DNA used to direct synthesis of
cellular components
• Control of gene expression leads to different cells/
tissue types
– Cells process environmental information
• Glucose levels, presence of hormones
– Cells in multicellular organisms must
coordinate with each other
36
• Nonequilibrium state
– Living systems are open systems
– Constant supply of energy needed
– Self-organizing properties at different levels
– Emergent properties from collections of
molecules, cells, and individuals
37
