Chapter 1 Lecture [Compatibility Mode]

8/7/2019 Chapter 1 Lecture [Compatibility Mode]

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Chapter 1 A.P.

Themes


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Lifes basic characteristic is a high degree oforder.

Biological organization is based on a

hierarchy of structural levels, each buildingon the levels below.

At the lowest level are atoms that are orderedinto complex biological molecules.

Many molecules are arranged into minutestructure called organelles, which are thecomponents of cells.

1. Each level of biological organization hasemergent properties

Copyright 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Fig. 1.2(2)


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Cells are the subunits of organisms, the unitsof life.

Some organisms consist of a single cells, others aremulticellular aggregates of specialized cells.

Whether multicellular or unicellular, all organisms

must accomplish the same functions: uptake andprocessing of nutrients, excretion of wastes,

response to environmental stimuli, and reproductionamong others.


Fig. 1.2(3)


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Multicellular organisms exhibit three majorstructural levels above the cell: similar cells aregrouped into tissues, several tissues coordinate

to form organs, and several organs form anorgan system. For example, to coordinate locomotory movements,

sensory information travels from sense organs to thebrain, where nervous tissues composed of billions of

interconnected neurons, supported by connectivetissue, coordinate signals that travel via other neuronsto the individual muscle cells.


Fig. 1.2(4) Fig. 1.2(5)


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Organisms belong to populations, localizedgroup of organisms belonging to the samespecies.

Populations of several species in the samearea comprise a biological community.

These populations interact with their physicalenvironment to form an ecosystem.

Fig. 1.2(6)


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Investigating biology at its many levels isfundamental to the study of life.

Biological processes often involve several levels ofbiological organization.

The coordinated strike of a rattlesnake at a mouserequires complex interactions at the molecular, cell,tissue, and organ levels within its body.

The outcome impacts not only the well-being of thesnake and the mouse but also the populations of bothwith implications for their biological community.

Many biologists study life at one level but gain a

broader perspective when they integrate theirdiscoveries with processes at other levels.



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Novel properties emerge at each stepupward in the biological hierarchy.

These emergent properties result frominteractions between components.

A cell is certainly much more than a bag ofmolecules.

This theme of emergent properties accentsthe importance of structural arrangement.

The emergent properties of life are not

supernatural, but simply reflect a hierarchyof structural organization.



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Life resists a simple, one-sentencedefinition, yet we can recognize life by what

living things do.


Fig. 1.3


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The complex organization of life presents adilemma to scientists seeking to

understand biological processes.We cannot fully explain a higher level oforganization by breaking down to its parts.

At the same time, it is futile to try to analyzesomething a complex as an organism or cell

without taking it apart.

Reductionism, reducing complex systemsto simpler components, is a powerfulstrategy in biology.

Reductionism is balanced by the longer-range objective of understanding emergentproperties.



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The cell is the lowest level of structure that iscapable of performing allthe activities of life.

The first cells were observed and named by

Robert Hooke in 1665 from slice of cork. His contemporary, Anton van Leeuwenhoek,

first saw single-celled organisms in pondwater and observed cells in blood and

sperm.

2. Cells are an organisms basicunit of structure and function



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In 1839, Matthais Schleiden and TheodorSchwann extrapolated from their own

microscopic research and that of others topropose the cell theory.

The cell theory postulates that all living thingsconsist of cells.

The cell theory has been extended to includethe concept that all cells come from other cells.

New cells are produced by division of existing cells,the critical process in reproduction, growth, andrepair of multicellular organisms.



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All cells are enclosed by a membrane thatregulates the passage of materials between

the cell and its surroundings. At some point, all cells contain DNA, the

heritable material that directs the cellsactivities.

Two major kinds of cells - prokaryotic cellsand eukaryotic cells - can be distinguishedby their structural organization.

The cells of the microorganisms called bacteriaand archaea are prokaryotic.

All other forms of life have the more complexeukaryotic cells.


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In contrast, in prokaryotic cells the DNA isnot separated from the cytoplasm in a

nucleus. There are no membrane-enclosed

organelles in the cytoplasm.

Almost all prokaryotic cells have toughexternal cell walls.

All cells, regardless of size, shape, orstructural complexity, are highly ordered

structures that carry out complicatedprocesses necessary for life.



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Biological instructions for ordering the

processes of life are encoded in DNA(deoxyribonucleic acid).

DNA is the substance of genes, the units ofinheritance that transmit information from

parents to offspring.

3. The continuity of life is based on heritableinformation in the form of DNA



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Fig. 1.5

Each DNAmolecule is

composed of twolong chainsarranged into adouble helix.

The buildingblocks of thechain, four kindsof nucleotides,convey

information by thespecific order ofthese nucleotides.


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How a device works is correlated with itsstructure - form fits function.

Analyzing a biological structure gives usclues about what it does and how it works.

Alternatively, knowing the function of astructure provides insight into its

construction.

4. Structure and function are correlatedat all levels of biological organization



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Organisms exist as open systems thatexchange energy and materials with theirsurroundings.The roots of a tree absorb water and nutrients

from the soil.The leaves absorb carbon dioxide from the air

and capture the energy of light to drivephotosynthesis.

The tree releases oxygen to its surroundings andmodifies soil.

Both an organism and its environment areaffected by the interactions between them.

5. Organisms are open systems that interactcontinuously with their environments



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The dynamics of any ecosystem includesthe cycling of nutrients and the flow ofenergy.

Minerals acquired by plants will be returned tosoil by microorganisms that decompose leaflitter, dead roots and other organic debris.


Energy flow

proceeds fromsunlight tophotosyntheticorganisms

(producers) toorganisms thatfeed on plants(consumers).

Fig. 1.7


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Organisms obtain useful energy from fuelslike sugars because cells break themolecules down in a series of closelyregulated chemical reactions.

Special protein molecules, called enzymes,catalyze these chemical reactions.Enzymes speed up these reactions and can

themselves be regulated.

When muscle need more energy, enzymes catalyzethe rapid breakdown of sugar molecules, releasingenergy.

At rest, other enzymes store energy in complex sugars.

6. Regulatory mechanisms ensure adynamic balance in living systems



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Many biological processes are self-regulating, in which an output or product of a

process regulates that process. Negative feedback or feedback inhibition

slows or stops processes.

Positive feedback speeds a process up.


Fig. 1.8


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A negative-feedback system keeps the bodytemperature of mammals and birds within a narrowrange in spite of internal and external fluctuations.

A thermostat in the brain controls processes that holdsthe temperature of the blood at a set point.

When temperature rises above the set point, an

evaporative cooling system cools the blood until it

reaches the set point at which the system is turned off. If temperature drops below the set point, the brains

control center inactivates the cooling systems andconstricts blood to the core, reducing heat loss.

This steady-state regulation, keeping an internal

factor within narrow limits, is called homeostasis.



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While positive feedback systems are lesscommon, they do regulate some

processes.For example, when a blood vessel is injured,

platelets in the blood accumulate at the site.

Chemicals released by the platelets attract

more platelets.The platelet cluster initiates a complex

sequence of chemical reactions that seals thewound with a clot.

Regulation by positive and negativefeedback is a pervasive theme in biology.



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Diversity is a hallmark of life.

At present, biologists have identified and namedabout 1.5 million species.

This includes over 280,000 plants, almost 50,000

vertebrates, and over 750,000 insects.

Thousands of newly identified species are addedeach year.

Estimates of the total diversity of life range

from about 5 million to over 30 millionspecies.

7. Diversity and unity are thedual faces of life on Earth



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In the face of thiscomplexity, humansare inclined tocategorize diverseitems into a smallernumber of groups.

Taxonomy is thebranch of biology thatnames and classifiesspecies into a

hierarchical order.


Fig. 1.10


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Until the last decade, biologists dividedthe diversity of life into five kingdoms.

New methods, including comparisons ofDNA among organisms, have led to areassessment of the number andboundaries of the kingdoms.Various classification schemes now include

six, eight, or more kingdoms.

Also coming from this debate has beenthe recognition that there are three evenhigher levels of classifications, thedomains.The three domains are the Bacteria,

Archaea, and Eukarya.


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Both Bacteria and Archaea have prokaryotes.

Archaea may be more closely related to

eukaryotes than they are to bacteria. The Eukarya

includes atleast fourkingdoms:Protista,Plantae,Fungi, andAnimalia.


Fig. 1.11


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Underlying the diversityof life is a striking unity,especially at the lowerlevels of organization.

The universal geneticlanguage of DNA unitesprokaryotes, like

bacteria, witheukaryotes, likehumans.

Among eukaryotes,

unity is evident in manydetails of cell structure.


Fig. 1.12


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Charles Darwin brought biology into focusin 1859 when he presented two main

concepts in The Origin of Species.


The first was thatcontemporary species arose

from a succession ofancestors through descent

with modification (evolution).

The second was that the

mechanism of evolution isnatural selection.

Fig. 1.14


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Fig. 1.15


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Fig. 1.17b

The finches of the Galapagos Islands diversifiedafter an initial colonization from the mainland toexploit different food sources on different islands.


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Descent with modification accounts for boththe unity and diversity of life.

In many cases, features shared by two speciesare due to their descent from a commonancestor.

Differences are due to modifications by natural

selection modifying the ancestral equipment indifferent environments.

Evolution is the core theme of biology - aunifying thread that ties biology together.



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The word scienceis derived from a Latinverb meaning to know.

At the heart of science are people askingquestions about nature and believing thatthose questions are answerable.

The process of science blends two types of

exploration: discovery science andhypothetico-deductive science.

9. Science is a process of inquiry thatincludes repeatable observations and

testable hypotheses



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Science seeks natural causes for naturalphenomena.

The scope of science is limited to the studyof structures and processes that we canobserve and measure, either directly orindirectly.


Verifiable observationsand measurements arethe data of discovery

science.

Fig. 1.18


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In some cases the observations entail a planneddetailed dissection and description of a biologicalphenomenon, like the human genome.

In other cases, curious and observant peoplemake totally serendipitous discoveries.

In 1928, Alexander Fleming accidentally discoveredthe antibacterial properties of Pencilliumwhen this

fungus contaminated some of his bacterial cultures. Discovery science can lead to important

conclusions via inductive reasoning.

An inductive conclusion is a generalization that

summarizes many concurrent observations.



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The observations of discovery science leadto further questions and the search foradditional explanations via the scientific

method.


The scientific methodconsists of a series ofsteps.

Few scientists adhererigidly to thisprescription, but at itsheart the scientific

method employshypothetico-deductivereasoning. Fig. 1.19


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A hypothesis is a tentative answer to somequestion.

The deductive part in hypothetico-deductivereasoning refers to the use of deductive logicto test hypotheses.

In deduction, the reasoning flows from the general

to the specific.From general premises we extrapolate to a

specific result that we should expect if thepremises are true.

In the process of science, the deduction usuallytakes the form of predictions about what weshould expect if a particular hypothesis is correct.



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The research by David Reznick and JohnEndler on differences between populations

of guppies in Trinidad is a case study of thehypothetico-deductive logic.

Guppies, Poecilia reticulata, are small fish thatform isolated populations in small streams.

These populations are often isolated by waterfalls.

Reznick and Endler observed differences inlife history characteristicsamongpopulations.

These include age and size at sexual maturity.



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Variation in life history characteristics arecorrelated with the types of predators present.

Some pool have a small predator, a killifish, which

preys predominately on juvenile guppies.

Other pools have a larger predator, a pike-cichlid,

which preys on sexually mature individuals.

Guppy populations that live with pike-cichlids are

smaller at maturity and reproduce at a youngerage on average than those that coexist withkillifish.

However, the presence of a correlation does not

necessarily imply a cause-and-effect relationship. Some third factor may be responsible.



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These life history differences may be due todifferences in water temperature or to someother physical factor.Hypothesis 1: If differences in physical

environment cause variations in guppy lifehistories

Experiment: and samples of different guppy

populations are maintained for severalgeneration in identical predator-free aquaria,

Predicted result: then the laboratorypopulations should become more similar in lifehistory characteristics.

The differences among populationspersisted for many generations, indicatingthat the differences were genetic.



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Reznick and Endler used a transplantexperiment to test the hypothesis that

predators caused life history differencebetween populations of guppies.

Fig. 1.21


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Reznick and Endler used controlledexperimentsto make comparisons betweentwo sets of subjects - guppy populations.The set that receives the experimental treatment

(transplantation) is the experimental group.

The control groupwere guppies who remained inthe pike-cichlid pools.

Such a controlled experiment enablesresearchers to focus on responses to asingle variable.Without a control group for comparison, there

would be no way to tell if it was the killifish orsome otherfactors that caused the populationsto change.



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Based on these experiments, Reznick andEndler concluded that natural selection due

to differential predation on larger versussmaller guppies is the most likelyexplanation for the observed differences inlife history characteristics.

Because pike-cichlids prey preferentially onmature adults, guppies that mature at a youngage and smaller size will be more likely toreproduce at least one brood before reachingthe size preferred by the predator.

The controlled experiments documentedevolution under natural settings in only 11years.



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Facts, in the form of verifiable observationsand repeatable experimental results, are the

prerequisites of science. Science advances, however, when new

theory ties together several observationsand experimental results that seemed

unrelated previously. A scientific theory is broader in scope, more

comprehensive, than a hypothesis.

They are only widely accepted in science if theyare supported by the accumulation of extensiveand varied evidence.



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It is not unusual that several scientists areasking the same questions.

Scientists build on earlier research and payclose attention to contemporary scientists inthe same field.

They share information through publications,

seminars, meetings, and personalcommunication.

Both cooperation and competitioncharacterize the scientific culture.

Scientists check each others claims byattempting to repeat experiments.

Scientists are generally skeptics.Copyright 2002 Pearson Education, Inc., publishing as Benjamin Cummings


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1 ) cience and technology are


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Science and technology are associated. Technology results from scientific discoveries

applied to the development of goods andservices.

The discovery of the structure of DNA by Watsonand Crick sparked an explosion of scientificactivity.

These discoveries made it possible to manipulate

DNA, enabling genetic technologists to transplantforeign genes into microorganisms and mass-produce valuable products.

1 ) cience and technology arefunctions of society



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DNA technology and biotechnology hasrevolutionized the pharmaceutical industry.

It has also had an important impact onagriculture and the legal profession.


Fig. 1.23


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