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Chapter 01

Lecture Outline

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

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The Science of BiologyChapter 1

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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

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• 7 characteristics of all living organisms1. Cellular organization2. Ordered complexity3. Sensitivity4. Growth, development, and reproduction5. Energy utilization6. Homeostasis7. 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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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


– 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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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 10

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

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Observation

Question

Potentialhypotheses

Remainingpossiblehypotheses

Last remainingpossiblehypothesis

Hypothesis 1

Hypothesis 2

Hypothesis 3Hypothesis 4

Hypothesis 5

Hypothesis 2

Hypothesis 3Hypothesis 5

Hypothesis 5

Rejecthypotheses1 and 4

Experiment

Rejecthypotheses2 and 3

Experiment

Modify hypothesis

Experiment 4Experiment 1

Predictions

Experiment 2 Experiment 3

Predictionsconfirmed 14

• 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

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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:

Brokenneckof flask

Flask is sterilizedby boiling the broth.

Unbroken flaskremains sterile.

Broken flask becomescontaminated afterexposure 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 contaminatenutrient broth.

Prediction: Sterilized broth will remain sterile if microorganisms are prevented from entering flask.

Spontaneous Generation Hypothesis: Living organisms will spontaneouslygenerate from nonliving organic molecules in broth.

Prediction: Organisms will spontaneously generate from organic moleculesin broth after sterilization.

Result: No growth occurs in sterile swan-necked flasks. When the neck isbroken 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

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• 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.

NORTHPACIFICOCEAN

Marquesas

SocietyIslands

Straits of Magellan

Cape Horn Tierra del Fuego

SOUTHATLANTIC

OCEAN

NewZealand

Hobart

King George’sSound

MauritiusBourbon Island

NORTHPACIFICOCEAN

PhilippineIslands

British Isles

WesternIsles

EUROPE ASIA

Madagascar

FriendlyIslands

Equator

NORTHAMERICA

GalápagosIslands

NORTHATLANTIC

OCEAN

Cape VerdeIslands

CanaryIslands

AFRICA

Sydney

AUSTRALIA

INDIANOCEAN

Cape ofGood Hope

FalklandIslands

Valparaiso

SOUTHAMERICA

Port DesireBuenos AiresMontevideo

KeelingIslands

Bahia

Ascension

St. HelenaRio 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

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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

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2

6

18

54

46

8

geometric progressionarithmetic 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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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


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

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• 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

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• 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

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