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Preliminary Biology Topic 3 “Life on Earth”copyright © 2005-22008 keep it simple sciencewww.keepitsimplescience.com.au

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1

What is this topic about?To keep it as simple as possible, (K.I.S.S.) this topic involves the study of:1. THE ORIGINS OF LIFE ON EARTH

2. THE HISTORY OF LIFE ON EARTH3. THE PROCARYOTIC ORGANISMS TODAY

4. THE VARIETY OF LIFE & HOW WE CLASSIFY

but first, an introduction...Biological Evolution“Evolution” means to undergo a sequence ofchanges. The change is NOT random... it followsa sequence or pattern.

There is overwhelming scientific evidence that

LIFE ON EARTH HAS CHANGEDover millions of years, and that there is adefinite pattern in the changes... life hasevolved.

In this topic you will study the

FACTS OF EVOLUTION ...what we know about the pattern of changes tolife on Earth over millions of years.

In a later topics you will study the

THEORY OF EVOLUTION...the scientific theory which attempts to explainhow and why evolution of life occurs.

The Variety of LifeEstimates vary enormously, but there areundoubtably millions of different types (species)of living things on Earth today. This variety isjust a tiny fraction of all the different types thathave ever lived.

How can we study and understand suchdiversity? Only by developing a system to

classify organisms into groups.You already know about grouping like-thingstogether:

In this topic you will study the way that sciencedeals with the staggering diversity of life on Earth.

Preliminary Biology Topic 3

LIFE ON EARTH

Plantsare

differentto

animals...

dolphins are exactly unlikecentipedes...

and jellyfishand

mushroomshave no

similaritiesexcept their

generalshape.




2

The EarlyEarth

Technologiesthat help usUnderstand Changing

Ideas

Science &

CulturalBeliefs

The Need to Classify&

Criteria used

DichotomousKeys

The Classification System

Changesto the

System?

Technolgiesto Study

Procaryotes

PossibleEnvironments in

Which LifeBegan

The MainSteps

LIFEon

EARTH

Origins ofLife on Earth

History ofLife on Earth

ProcaryoticOrganisms

Today

Variety of Life&

How We ClassifyThe

Archaea

Theoriesof

Origins of Life

CONCEPT DIAGRAM (“Mind Map”) OF TOPICSome students find that memorising the OUTLINE of a topic helps them learn and remember

the concepts and important facts. As you proceed through the topic, come back to this page regularly to see how each bit fits the whole.

At the end of the notes you will find a blank version of this “Mind Map” to practise on.




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In the Beginning...

We believe the Earth is about 4.6 billion(= 4,600 million) years old. How do weknow? That will be dealt with later.

The Earth of 4 billion years ago wasvery different to that of today.

How do we know that? Well, we cannotbe 100% sure, but this descriptionmatches with:-

• conditions & chemicals on other planets.

• the chemicals that erupt from volcanicvents today, and probably always have.

Chemicals First, Then CellsWe think that he atmosphere of the primitive Earth contained exactly

the same elements that the chemicals of life are made from... mainly carbon, hydrogen, oxygen & nitrogen.

In the 1920’s it was suggested by two scientists independently, that maybe the conditions on Earth 4 billion years ago:-

• firstly caused chemical reactions that made complex organic molecules.• then these chemicals somehow came together to form living cells.• and once life got started, it evolved into all the species in the

fossil record and alive today.

1. THE ORIGINS OF LIFE ON EARTH

Volcanoesadd manygases to

atmosphere

Strong U.V.rays from Sun Atmosphere of

H22O vapour,methane,ammonia,

carbon dioxide,nitrogen,hydrogen.

NO free oxygen

Spontaneous Generation of Life

Until about 150 years ago, it wasgenerally believed that life could appearspontaneously... maggots just“happened” in rotting meat and frogsjust “arise” from swampy ground.

This concept was finally proven wrongby Louise Pasteur’s famous experimentof 1862...

...and by the 1880’s the cell theory of lifewas established as a scientificprinciple.

This includes the statement that “allcells (life) come(s) from pre-existingcells (life)”.

So how did the first living thingsget started on the primitive Earth?

Each flask contains a “broth”,boiled until sterilized

CClloosseedd ffllaasskkrreemmaaiinnss

sstteerriillee...... nnoommiiccrroobbeessggrrooww iinn iitt..

OOppeenn ffllaasskk ggrroowwssmmiiccrroobbeess && rroottss..IItt wwaass bbeelliieevveeddtthhee lliiffee ccaammee

ssppoonnttaanneeoouussllyyffrroomm ccoonnttaacctt

wwiitthh aaiirr..

TThhiiss ffllaasskk iiss ooppeenn ttoo tthheeaaiirr,, bbuutt tthhee ““ggoooosseenneecckk””pprreevveennttss aaiirrbboorrnnee ssppoorreess

ggeettttiinngg ttoo tthhee bbrrootthh..IItt rreemmaaiinneedd sstteerriillee,, aannddpprroovveedd ““ssppoonnttaanneeoouussggeenneerraattiioonn”” iiss wwrroonngg..

Violent storms - a lot of Lightning

Earlyoceans



4

Significance of the Urey-Miller Experiment

1. It demonstrates the way Scienceworks, by formulating an hypothesisand then testing it by experiment. In thiscase the hypothesis was put forward byother scientists 30 years before theexperiment was done.

2. Although it didn’t prove how life gotstarted on Earth, the experimentalresults support the hypothesis byshowing that life-forming chemicalscould have been produced naturallyunder the conditions of the primitiveEarth.

3. In combination with evidence from:

• Space Exploration• Vulcanology & Earth Chemistry• Ancient Rocks & Fossils• Study of “Primitive” Life Alive Today

and other areas of scientific study, theUrey-Miller experiment is just one partof a “package” of evidence that seemsquite consistent with the idea that lifeformed naturally on the primitive Earthsome 4 billion years ago, and hasevolved into what we see today.

We cannot prove how life arose, but theweight of evidence suggests we’re onthe right track.


This was one of the most famousexperiments in the history of Biology. Itwas designed in the 1950’s to test the firstpart of the hypothesis about the origins oflife... that the conditions of the primitiveEarth could naturally produce the complexmolecules necessary for life to start.

The initial experiments resulted in theproduction of sugars and amino acids,and later variations produced thechemical building blocks for cellmembranes, and even for DNA.

THIS SUPPORTS THE FIRST PART OFTHE HYPOTHESIS... the chemicals oflife could have appeared spontaneouslyon the primitive Earth.

““OOcceeaann””FFllaasskkbbeeggaannwwiitthhppuurreewwaatteerr

“Atmosphere” Flask

HEAT

Vapo

urs

circ

ulat

e

Electricspark

simulateslightning

Condensercools vapours

back toliquids

““LLiiqquuiidd TTrraapp””wwaass llaatteerr ffoouunndd ttoo

ccoonnttaaiinn oorrggaanniicccchheemmiiccaallss,, ssuucchh aassssuuggaarrss aanndd aammiinnooaacciiddss...... tthhee bbaassiicccchheemmiiccaallss ooff lliiffee..

MMiixxttuurree ooff ggaasseess ttoo ssiimmuullaatteepprriimmiittiivvee aattmmoosspphheerree..mmeetthhaannee((CCHH4)),, CCOO2,,

aammmmoonniiaa ((NNHH3)),, NN2,, HH2

The Urey-Miller Experiment

Life From Outer Space?The hypothesis that Urey &Miller tested is not the onlyidea for the origins of life.

It has been suggested that thefirst living things on Earth (orat least the chemicals theyformed from) could have comefrom outer space.

This is an interestingidea, but so far theweight of evidence

supports the hypothesisthat Earth life arose on

Earth, and notsomewhere else.



5

This is one of the key technologies inour search for an understanding of theorigins of life. It is the method thatallows us to measure the age of rocks &fossils.

The atoms of each chemical element arenot all exactly the same. They have thesame number of protons & electrons(that’s what makes them that element),but the number of neutrons in the atomcan vary. Such atoms of the sameelement, but with a different number ofneutrons, are called “isotopes”. Someisotopes are “radio-active” and give offnuclear radiations... hence “radio-isotopes”.

Radio-isotopes “decay” at a predictablerate. That is, the level of radiation diesdown over time in an exactmathematical way.

This “Radiometric Dating” is how weknow the age of the Earth, ofdifferent fossils etc, and can

describe the entire history of life onEarth fairly precisely.


TIME

RAD

IATI

ON

LEVE

L

ffrroomm hheerree

to hh

erre

to here

110000

5500

2255

00

hhaallff-lliiffeehhaallff-lliiffee hhaallff-lliiffee

TThhee ttiimmee iitt ttaakkeessffoorr tthhee rraaddiiaattiioonnttoo ddrroopp ttoo hhaallff

tthhee pprreevviioouuss lleevveelliiss ccoonnssttaanntt.. TThhiiss iiss tthhee

“Half-llife”

Technologies That Help Us Understand

By measuring the amount of radiationpresent now, and knowing the “half-life”of the isotope, the age of objects can becalculated.

The most famous example is “CarbonDating” which uses an isotope ofcarbon (called “carbon-14”) to find theage of artifacts from human history.

Carbon-14 has a half-life of about 5,700years, so if a bone orwooden tool ismeasured to haveonly 1/2 as muchradiation as it wouldhave had originally,then one half-life hasgone by since that bone or tree died...therefore, it must be 5,700 years old.

Carbon-14 is not much use beyondabout 40,000 years, but there are otherisotopes (e.g. potassium and uranium)with half-lives of many millions of years.These can measure the ages of fossilsand rocks which formed millions, oreven billions of years ago.

Radiometric Dating

The Electron MicroscopeThis device was mentioned in Topic 2 as having a major impact

on our understanding of cells and cell structures.

Electron microscopes can also allow scientists to studyvery ancient fossil cells in rocks and to make

comparisons with some types of “primitive” cells whichstill live today. This gives us further clues about how

ancient life-forms lived and evolved.




6

Biochemical Analysis & DNA Technology

It’s well known from TV crime dramasthat by analysing traces of DNA from acrime scene, a criminal can bepositively identified.

The technique is also used to identifythe remains of victims of war or naturaldisasters. By comparing DNA samplesfrom a body part with samples from therelatives of missing people, scientistscan positively determine which familythe victim is from.

The same technique can be used to findthe “relatedness” of different livingthings, and even give estimates of howlong ago 2 related species divided fromeach other, in an evolutionary sense.

For example, DNA studies suggeststrongly that humans and chimpanzeesare closely related; our DNA is 99%identical.

Our ancestors and chimp ancestorsmust have separated only about 5million years ago.

We’re prettycertain about

this, even thoughthe relevant

fossils have notbeen discovered.

More generally, biochemistry and DNAstudies have shown:

• all life forms on Earth are related. Thismeans that all living things todayevolved from one original type.

• which types are more closely, or moredistantly, related.

This complements the evidence of thefossil record, to give us a clearer pictureof the exact sequence of evolution.

Fill in the blank spaces.

We believe that the Earth of 4 billionyears ago had an atmospherecontaining gases such as(a).........................., (b)..........................and (c)......................................... but nouncombined (d)............................. Therewere many (e)........................... erupting,and violent storms producing a lot of(f)..................................(g)......................... radiation from the sunwas at high levels.

Under these conditions, it is possiblethat complex (h)..................... chemicalscould form naturally. The (i).....................& ........................ experiment supportedthis hypothesis. The experimentinvolved simulating the conditions ofthe primitive Earth, and after some timeit was found that (j)...............................and (k)................................ had formed.

Another hypothesis for how life beganon Earth is that living cells, or at leastthe chemicals they formed from camefrom (l)...............................................

Radio-metric dating is a techniquewhich measures the (m)...........................from radio-active (n).................................The age of rock or fossil etc can becalculated from the (o)....................-lifeof the isotope.

The electron microscope has not onlyhelped our understanding of livingcells, but also helps us discover andstudy ancient (p)....................... in rocks.

DNA technology adds to ourunderstanding of the evolution of lifeby determining how closely(q)........................................ differentorganisms are.

Worksheet 1 Origins of Life



7


Multiple Choice1. Which of the following was probably NOT acommon gas in the atmosphere on Earth 4billion years ago?A. Carbon dioxideB. OxygenC. MethaneD. Ammonia

2. Louise Pasteur’s famous “gooseneck flask”experiment of 1862 proved that:A. life could begin spontaneously from contactwith air.B. organic compounds could not have beenproduced naturally on the primitive Earth.C. a nutrient broth rots after contact with air.D. the theory of “spontaneous generation” waswrong.

3.In the Urey-Miller experiment:A. organic molecules were produced frominorganic.B. living cells were produced from non-livingchemicals.C. microsphere membrane structures weremade artificially.D. complex inorganic molecules wereproduced.

4. The technology that has allowed us toaccurately measure the age of rocks, fossilsand the Earth itself is:A. radio-isotope studies.B. electron microscope.C. the “principle of superposition” of fossils.D. DNA sequencing.

Longer Response QuestionsMark values given are suggestions only, and areto give you an idea of how detailed an answer isappropriate. Answer in the spaces provided.

5. (6 marks) Describe the conditions on Earth 4 billion yearsago, covering:a) significant physical conditions

b) chemical composition of the atmosphere.

6. (5 marks) Give an outline of the Urey-Miller experiment,including:a) the hypothesis it set out to test.

b) a basic description of what was done.

c) the main results.

d) what conclusion may be drawn from it.

7. (3 marks)a) Explain how radio-isotopes have contributedto our understanding of the history of life onEarth.

b) Identify another recently developedtechnology and outline its contribution to ourknowledge of the history of life.

Worksheet 2 Practice Questions (Section 1)




8

Summary of the Main EventsThe following time-line identifies the majorstages in the evolution of life on Earth. The mainevidence for this has come from fossilspreserved in sedimentary rocks. The timessuggested are approximate, but based on radio-metric studies of the rocks.

Formation of Organic Molecules

This probably began as soon as theEarth was cool enough forthe molecules to existwithout being torn apartagain. The Urey-Millerexperiment (and manyothers since) prove thatsugars, amino acids, lipidsand even the buildingblocks of DNA and RNAcould form spontaneouslyin the chemical conditionsof the primitive Earth.

Eventually, by 4 billion years ago, theearly oceans must have become achemical “soup”, highly concentrated inorganic molecules.

Molecules Formed MembranesIt is thought that the next crucial step

was the formation of membranes. In thewatery environment of the oceans,hydrophobic (“water-hating”) moleculesnaturally tend to cling together, like oilforming droplets in water. Experimentshave shown that some lipid moleculesin water will, quite naturally, form“microspheres” with other chemicalstrapped inside.

A microsphere is not a living cell, butscientists believe that structures likethis were the precursors of cells.

2. THE HISTORY OF LIFE ON EARTH

Millions ofyears ago

4,500

4,000

3,500

3,000

2,500

1,000

500

0

1,500

2,000

Earth formed

Organic moleculesforming as suggested

by the Urey-MMillerexperiment?

Molecules formedmembranes?

First living thingssomewhere here (?)

Throughout this immenseperiod all life was bacteria-

like, anaerobic (living withoutoxygen) and heterotrophic,

feeding on the organicmolecules of the

environment.

First autotrophs?chemosynthetic bacteria

FFiirrsstt CCyyaannoobbaacctteerriiaa,, uussiinnggcchhlloorroopphhyyllll ffoorr pphhoottoossyynntthheessiiss

aanndd rreelleeaassiinngg ooxxyyggeenn

OOvveerr tthhiiss ttiimmee tthhee EEaarrtthh wweenntt ffrroommbbeeiinngg AANNOOXXIICC ttoo OOXXIICC..

OOrrggaanniissmmss uussiinngg ooxxyyggeenn ffoorrcellular respiration aappppeeaarreedd..

First sexualreproduction.

Evolution speeds up

AAnniimmaallss wwiitthh hhaarrdd ppaarrttss ((sshheellllss eettcc))aappppeeaarr.. HHuuggee iinnccrreeaassee iinn ffoossssiillss

FFiisshhAAmmpphhiibbiiaannss,, IInnsseeccttssRReeppttiilleess,, MMaammmmaallssDDiinnoossaauurrssBBiirrddssHHuummaannss

11

33

44

55

77

88

99

66

22

OOnnee lliippiidd mmoolleeccuullee

Lipid moleculescling together,

forming a“microsphere”

OOtthheerr cchheemmiiccaallssmmaayy bbee

ttrraappppeedd iinnssiiddee

FFiirrsstt mmuullttiicceelllluullaarr ppllaannttss ((aallggaaee))aanndd aanniimmaallss

((ssppoonnggeess,, wwoorrmmss,, jjeellllyyffiisshh))

FFiirrsstt EEuuccaarryyoottiicc cceellllss((wwiitthh mmeemmbbrraannee-bbaasseedd

oorrggaanneelllleess))

1

2



9

The First Living Cellsmust have been microspheres which

trapped inside themselves a mixture ofchemicals that could attract othermolecules in through the “membrane”so they became bigger (i.e. feeding &growing) and also cause copies of theirown molecules to be built... small RNAmolecules can do this.

Eventually thesphere wouldsplit in two,(reproduction!)each part witha share of theessentialchemicals tomake it all happen over again.

We can’t be sure when this happened,but by about 3.8 billion years ago wefind chemical evidence of living cells insome rocks, and by 3 billion years agothere are fossils of bacteria-like cells, invarious forms... they were evolving intonew types already.

These cells lived without oxygen(“anaerobic”) and were probablyfeeding on the “soup” of organicmolecules still in the oceans.

A Billion Years of Scavenging

For perhaps 1,000 million years themost advanced organisms on Earthwere bacteria-like cells which livedwithout oxygen, and scavenged theorganic “soup” of organic molecules inthe oceans.

Probably the production of organicmolecules (“food”) was still occurringas in the Urey-Miller experiment, but thewhole regime was about to change...

The First Autotrophs

Chemosynthesis & Photosynthesis

About 2.8 billion years ago, a new typeof bacteria appears in the fossil record.The fossils appear similar toautotrophic bacteria alive today, whichmake their own food, using energy fromchemicals in the environment. Thisprocess is called “Chemosynthesis”.(details later)

By 2.3 billion years ago, fossils of cellsrecognisable as cyanobacteria appeared.These are bacterial type cells, but usechlorophyll to trap sunlight, and produceOXYGEN as their waste product.

They grew in shallow seas in structurescalled “stromatolites” which we find ascommon fossils in rocks from this time.Living stromatolites still grow in someplaces today.


3

4

5

LivingStromatolites

Photo by Pat Bride

WATER + CARBON GLUCOSE + OXYGENDIOXIDE

6H22O + 6CO22 C66H1122O66 + 6O22

cchhlloorroopphhyyllll

lliigghhtt eenneerrggyy

Living mat ofcells in thin

top layerColumn grows like a

stalagmite. New layersgrow on top of old,

dead layers



10

The World Goes Oxic

Up until this time the Earth was“anoxic”... completely without anyuncombined molecular oxygen (O2).There were plently of oxygen atoms ofcourse, but they were all chemicallycombined in water (H2O) and CO2 andvarious other compounds.

But now the cyanobacteria began“modern style” photosythesis inmillions of stromatolites, for millions ofyears...

We find huge deposits of evidence forwhat happened next... the world wentrusty!

In many parts of the world (includingWestern Australia) we find hugedeposits of “Banded Ironstone”; rockcontaining layers of iron oxide (Fe2O3).The iron mineral is very fine grained asif precipitated from a water solution.

The explanation is that, in the anoxicearly conditions a lot of iron wasdissolved in the oceans in the solubleform of Fe2+ ions. As the cyanobacteriabegan releasing vast quantities of O2oxygen, it reacted with the iron formingthe insoluble Fe2O3 iron oxide (which isRUST).

Eventually, after about 200 milion years,all the iron was precipitated, and nowthe oxygen began building up in theatmosphere... the air became “OXIC”.

This had four important consequences:-

1. The natural production of organicchemicals by the “Urey-Miller process”stopped forever. Oxygen is chemicallyactive enough to destroy organicmolecules as fast as they could form.

Life could never again start up the way it once did.

2. The old-type anaerobic bacteria foundoxygen poisonous, so many becameextinct. A few survived in environmentswhere there is no oxygen, and therethey live to this day... you will studythem soon.

3. Atmospheric oxygen alloweddevelopment of an ozone layer. Thisabsorbs UV rays and was vital for thelater development of life on land.

4. The oxic environment encouraged anew, more efficient way to use foodenergy... cellular respiration. By 2 billionyears ago the familiar modern cycle wasoperating:

ATP is the energy compound whichpowers all life processes... celldivision, moving, growing etc.


Light energy

GLUCOSE+

OXYGEN

CARBONDIOXIDE

+WATER

ATP

PHOTOSYNTHESIS(in cyanobacteria)

AEROBICRESPIRATION(in all living

things)

6



11

The First Eucaryotic Cells

All the “more advanced” living thingson Earth today are characterized bycells containing many organelles whichare built from and/or surrounded bymembranes. Such cells are called“eucaryotic”.(This was dealt with in Topic 2)

Prior to about 1.5 billion years ago, alllife on Earth was “procaryotic” meaningthat the cells lack a true nucleus,mitochondria, chloroplasts, etc. Theliving procaryotes of today are thebacteria and cyanobacteria. Withouttrue organelles to organize their cellfunctions better, the procaryotes haveto remain very tiny, single cells in whichdiffusion distances are small, and theSA/Vol ratio is high.

And that’s how life on Earth might haveremained forever, except some cells atesome smaller cells, but failed to digestthem. The small cells lived on insidetheir “host” in a relationship that soonbecame mutualism, and after millions ofyears, the ingested cells evolved tobecame “organelles” of the larger cell.


LLaarrggeerr cceellll eennvveellooppiinngg aa ssmmaalllleerr cceellll ffoorrffoooodd,, bbuutt ffaaiillss ttoo ddiiggeesstt iitt..

SSmmaalllleerr cceellll bbeeccoommeess mmiittoocchhoonnddrriioonnwwiitthhiinn tthhee ““hhoosstt”” cceellll

BByy aa ssiimmiillaarr pprroocceessss,, aapphhoottoossyynntthheettiicc cceellll iiss

““eeaatteenn”” aanndd bbeeccoommeess aa cchhlloorrooppllaasstt

Evolves tobecome anAnimal cell Evolves to

become aPlant cell

7 What’s the evidence for this?

• Both mitochondria & chloroplastscontain their own DNA, and it isbacteria-like DNA in a loop. These organelles reproduceindependently of the rest of the cell in a mini-version of a cell division.

• Mitochondria contain their own ribosomes for making their ownproteins.

• Mitochondrial enzymes (which controlcellular respiration) are attached to the inner membrane in a very bacteria-like way.

This whole idea is known as the“Endosymbiotic Hypothesis” and is ourbest explanation of where the first cellscame from that later evolved into theplants and animals.(“Endo-” = inside,

“symbiosis” = to live together)

Sex Speeds Things UpSo far in the history of life, all the living things

probably reproduced by simple cell division.This produces identical daughter cells. (ascovered in Topic 2) The only way a new variationcould occur was by occasional genetic“accidents” ... mutations. So the evolution ofnew types was very slow.

A little over 1 billion years ago, some cellsbegan exchanging bits of DNA with each other.Fossils have been discovered (using theelectron microscope) of 2 cells joined by a thintube apparently in “conjugation”, in which thecells swap DNA fragments in a kind of simplesexual fertilisation of each other.

The result is more genetic variations and moredifferences between individuals. Evolution hadmore opportunities, and sure enough, the fossilrecord shows an accelerating increase in new,more complex forms appearing.

8

CELLS in CONJUGATION

SSmmaallll ffrraaggmmeennttss ooff DDNNAA aarree ppaasssseedd tthhrroouugghhtthhee ttuubbee,, iinnccrreeaassiinngg tthhee ggeenneettiicc vvaarriiaattiioonnss

wwiitthhiinn aa ppooppuullaattiioonn



12

Similarly, some eucaryotic,heterotrophs became colonial to evolveinto the firstmulticellularanimals, similarto modernsponges. Latercame flatwormsand jellyfish-likecreatures withvery simple bodyplans.

About 600 million years ago there camean “explosion” of life. We find a hugeincrease in fossil numbers and forms,partly because some types developedshells and other hard body parts thatfossilized well.


9 The First Multicellular Organismsappeared about 800 million years ago.

It is often an advantage for an organismto be large. A larger organism deterspredators and gathers more of theresources of the environment, so itschance to survive and thrive is better.But, as you know from Topic 2, a singlecell cannot grow too large because theSA/Vol ratio gets less.

The other way to get large is have morecells.

About 800 million years ago someeucaryotic, photosynthetic cellsbecame “colonial”. When the cellsdivided, they didn’t separate, but stayedattached to each other, formingfilaments or flat sheets. These simple,multicellular associations evolved intothe algae group and from one type ofthem, came (eventually) the plants.

Science Clashes With Culture?Darwin’s Theory of Evolution causedtremendous controversy whenpublished in 1859 because it was notconsistent with the Biblical story of“divine creation” and many people sawthis as an attack on their religion andtheir culture.

Even today, there are some religiousgroups who reject the entire concept ofthe “Evolution of Life” because theyinterpret their traditional, cultural orreligious stories of creation veryliterally.

Most mainstream religions however,accept that Science is not trying toattack any belief, culture or tradition,but only to understand and explain thenatural world. Most religiousorganizations now accept the “Facts ofEvolution” that life on Earth has existedfor billions of years, and has undergoneprogressive change.

Many Christian churches, for example,accept the scientific evidence for theage of the Earth, the beginnings andhistory of life, and recognise that thecreation stories in “Genesis” are notliterally true, but are allegories to thepower and benevolence of the Judaic-Christian-Islamic God. The belief is thatevolution happened, but under God’scontrol and supervision, along apathway He ordained.

Thus it is quitepossible toreconcilereligious beliefand faith withscientificenquiry andknowledge.

Each contributes in its own way tohuman culture, and to each individual’s“humanity”.



13

Fossils have been known and collectedby people for thousands of years. InChina they were considered as “DragonBones”, while it was supposed byEuropeans up until the 1860’s thatfossils represented the many types ofanimal which never made it to Noah’sArk and so drowned in the BiblicalFlood.

The “Principle of Superposition” wasdeveloped by early Geologists and used tostart putting fossil discoveries into relativetime order, although the actual ages werenot known.

From many studies like this, the fossilsover the entire known span of Earthhistory were arranged in order.

Once this rough order of age for fossilswas established, scientists began to seethe pattern... the fossil record shows aclear pattern from few and simpletowards more varied and complex lifeforms.

It was partly this pattern in the fossilrecord that convinced Charles Darwinthat life on Earth had changed andevolved.

The fossils don’t just show that life onEarth has changed, but that is haschanged in a sequence, in a directionfrom “few & simple” to “more variety &more complex”.

Until the 20th century, little notice wastaken of the most ancient rocks onEarth, from the “Pre-cambrian” time.Few fossils could be detected in them,and it seemed that animal life hadsimply appeared in abundance at acertain point in time.

Improved technologies changed allthat...

Radio-metric dating of meteorites andMoon-rock told us the true age of theSolar System and therefore of the Earth.Dating of fossils and the ancient rocksput the sequence of the fossil recordinto a proper time-scale.

Improved microscopic techniques,especially the electron microscope,discovered the cellular fossils in theancient rocks. It was previously thoughtthere were no traces of life in the “Pre-cambrian” rocks.

Now with the insights into evolutionprovided by DNA technology, and thebiochemical experiments of Urey &Miller and many others, we canunderstand the fossil record and thehistory of life right back to its originswith some degree of scientificconfidence. We can’t know everything,but no longer believe in “dragonbones”.


ANCIENT TIMES MODERN TIMES

Less complexity More complexLess variety Greater varietyUnlike modern More and more like

life-fforms modern life-fforms

Rock profile in1st location

Rock profile in2nd location

These fossilscorrelate toeach other,

so thecorresponding

rock layers (in different

places) must be thesame age.

olde

styo

unge

stChanging Ideas About the History of Life




14


The age of the Earth is thought to beabout (a).............. billion years. Byabout 4 billion years ago (BYA) it islikely that many (b)..................................compounds had formed from theinorganic chemicals present.

The next step was probably that certainlipid molecules (which are(c).................................... =water hating)may have come together and formed(d)............................................ Thesestructures, in which the lipid layer actslike a (e)........................................., mayhave trapped other chemical inside.

If the chemicals inside were able to(f)........................................ themselves,and to attract other molecules inthrough the “membrane”, then thestructure is “alive”. This may have firsthappened about (g)...................... BYA.

For the next billion years, all life onEarth was bacteria-like, (h)......................(living without oxygen) andheterotrophic, feeding on the(i).................................. moleculesdissolved in the oceans.

The first (j)............................................(self-feeders) appeared about 2.5 BYA.They were able to make food using theenergy of (k)...........................................from their environment. The first cellsdoing photosynthesis were the(l)................. ................................., whichgrew in large structures called(m)............................................. Theyreleased (n)............................. gas whichreacted with dissolved (o).......................This precipitated and formed extensivesediments, which are known as(p)......................... .................................Eventually there was enough oxygenformed to turn the atmosphere frombeing (q)......................., to become oxic.

This was a disaster for many anaerobiccells, which became extinct. They werereplaced by new types which used(r)........................... ...........................(process) to release energy from theirfood in the form of the energy chemical(s)......................

About 1.5 BYA, the first(t)........................ cells (with membrane-based organelles) appeared. The bestexplanation for these is called the“(u).............................................................Hypothesis” in which one cell ingestedanother, but failed to(v)....................................... it. Thesmaller cell survived to live within thelarger, eventually becoming anorganelle such as a mitochondrion or(w)...................................Evidence supporting this hypothesis isthat some organelles contain their own(x).................. and .....................................for making proteins.

Roughly 1 BYA some cells beganswapping bits of DNA in a primitive sortof (y)................................ This increasedthe (z)...................................... variationand so evolution (aa)..............................

About 800 MYA, the first(ab)...................................... organismsappeared. The early forms resembled(ac)............................(plant) and(ad).................................. (animal).

About 600 MYA there was an“explosion” in the fossil record, whenmany animals with (ae)..........................body parts appeared.

WHEN COMPLETED, WORKSHEETS BECOME SECTION SUMMARIES

Worksheet 3 History of Life on Earth



15


Multiple Choice1. A “precursor” to the formation of the firstliving cells was probably:A. formation of an oxic environment.B. formation of chemical systems capable ofphotosynthesis.C. formation of “microsphere” membranestructures.D. polymerisation of natural inorganicchemicals.

2. The first living cells were probably:A. aerobic, procaryotic and autotrophic.B. anaerobic, procaryotic and heterotrophic.C. anaerobic, eucaryotic & chemosynthetic.D. anoxic, eucaryotic and heterotrophic.

3. It is thought that the organisms mainlyresponsible for the conversion of the Earth to an“oxic” environment were the:A. Archaea.B. chemosynthetic autotrophs.C. early eucaryotic algae.D. cyanobacteria.

4. The “Endosymbiotic Hypothesis” is aproposal for the formation of the first:A. procaryotic cells.B. photosynthetic cells.C. eucaryotic cells.D. cells capable of aerobic respiration.

5. The “Endosymbiotic Hypothesis” issupported by which of the following pieces ofevidence?A. Mitochondria have their own DNA.B. Cells regularly envelop and “eat” smallercells.C. Fossils of cells in “conjugation” have beendiscovered.D. Mitochondria can live independantly outsideof their “host” cell.

6. It is thought that the correct sequence ofcertain events in the history of life was:A. sexual reproduction, eucaryotic cells,multicellular.B. eucaryotic cells, multicellular, sexualreproduction.C. eucaryotic cells, sexual reproduction,multicellular.D. multicellular, sexual reproduction,eucaryotic cells.


7. (2 marks) Identify two major stages or processes that arebelieved to have occurred before theappearance of the first living cells on Earth.

8. (5 marks) One of the most significant events in thehistory of the Earth was the change from ananoxic to an oxic environment.

a) What does this mean?

b) Identify the organisms, and the process thatcaused the change.

c) Explain the significance of this change forthe evolution of life.

9. ( 4 marks)a) What does the “Endosymbiotic Hypothesis”attempt to explain?

b) Outline the hypothesis.

c) Give a piece of evidence supporting thehypothesis.





16

3. THE PROCARYOTIC ORGANISMS TODAYTechnology to Study Procaryotes

Even with a good light microscope, bacterial cells are so small that they appear as simple rods, spheres and spiral-shaped cells.

The Electron Microscope

With its superior magnification andresolution, the electron microscope wasthe technology that revealed the finedetails of cell structure. It was theelectron microscope that first gave usthe understanding of eucaryotic andprocaryotic cells as beingfundamentally different.

This understanding led to theclassification of all the procaryoticorganisms into the “kingdom Monera”,totally different life forms to the eucaryoticplants, animals and fungi.

Within this procaryotic kingdom of life,many different sub-groups wererecognized, but they were all thought tobe essentially alike because of theirprocaryotic structure. New technologieshave changed that view...

NNuucclleeuuss aanndd ootthheerr oorrggaanneelllleess mmaaddeeffrroomm oorr bboouunndd bbyy mmeemmbbrraanneess

NNuucclleeaarr rreeggiioonn,, bbuuttnnoo ttrruuee nnuucclleeuuss

PROCARYOTIC EUCARYOTICCELL CELL

RRiibboossoommeess iinn ccyyttooppllaassmm,,bbuutt nnoo mmeemmbbrraannee-bboouunndd

oorrggaanneelllleess

DNA & Protein Sequencing

These allow scientists to determine theprecise sequence of chemical units inDNA molecules and protein chains.

Studies on the different types ofprocaryotic organisms have shown thatthere are some types that are sodifferent from the rest, that theyperhaps should be placed into a newkingdom, to be called “Archaebacteria”or simply “Archaea” (pronounced ark-ee-a).

What’s different about them?They have:

• completely different RNA molecules toall other life.

• cell walls which are chemicallydifferent to all other life.

• totally different enzymes for releasing energy from food.

• different pathways of metabolism forsome cell processes.

The word “archae” means “ancient”,and it is believed that these verydifferent organisms are modernsurvivors from those primitive cells of 3billion years ago.

The ArchaeaWhen the cyanobacteria began photosynthesizing in their

stromatolites just over 2 billion years ago, the oxygenthey released firstly caused the oceans to rust, and then

caused the atmosphere to become oxic.

We think many of the older species of anaerobic life couldnot cope with oxygen and died out. Some however,

survived in habitats where there is no oxygen...



17

The methanogens get their energy fromthe chemical reaction:

carbon + hydrogen methane + waterdioxide

CO2 + 4H2 CH4 + 2H2O

It is their production of methane (CH4)that gives them their name.

As well as living in the decomposingsediments under water, somemethanogens live in the gut of animals.Other microbes help digest plant foodsby fermentation, producing CO2 & H2.The methanogens convert these gasesto methane... intestinal gas.


The methanogens are one type of theArchaea group. They cannot tolerateoxygen at all and live in habitats wherethere is none:

• in the muddy sediments underswamps, lakes and the seas.

• in the digestive systems of manyanimals, especially the ruminants, a group of grazing animals including cattle.

Their original habitat of 3 billion yearsago was the anoxic oceans with anatmosphere containing the gases theyneed... carbon dioxide and hydrogen.

As the oxygen levels rose many diedout, but the oxygen never reached someplaces such as the mud and sedimentsunder water, where the processes ofdecomposition remove any oxygenimmediately, and produce carbondioxide and hydrogen from thefermentation of dead plant material andother organics which settle into themud.

The Methanogens

The ThermoacidophilesThermoacidophiles are another group of theArchaea which are probably descended fromancient types. They love hot, acid conditions.(“Thermo-” = heat, “-acido-” = acid, “-phile” = loving.

The thermoacidophiles live today in extremehabitats which may be quite similar to thehabitats they lived in billions of years ago. Someare found in the boiling, acidic waters ofvolcanic hot springs, like these in New Zealand.

Others havebeendiscovered inthe deep ocean,around volcanicvents wherethey are thebasis of someweird foodchains that doNOT depend on photosynthesis.

Thermoacidophiles are autotrophs capable ofmaking their own food from simple inorganicchemicals like CO2 & H2O.

The energy needed to make food is not fromsunlight, as in photosynthesis, but from theenergy in certain naturally occurring inorganicchemicals... they are “chemosynthetic”.

The thermoacidophiles depend on hydrogensulfide (H2S) which is abundant in the volcanicsprings they live in. It is H2S which gives thecharacteristic “rotten-egg smell” of volcanicsprings. It is poisonous to most life-forms (notto mention the boiling temperatures and highlyacidic conditions) but to these Archaea cells it ishome-sweet-home, possibly just like thehabitats they inhabited 3 billion years ago on theyoung, volcanically-active Earth.

Some of the deep-sea chemosynthetic typeshave formed mutualistic relationships with gianttube worms, and are the basis of foodproduction in the totally dark ecosystemsthousands of metres deep. The chemosyntheticArchaea cells live inside the tube-worm’s body.The worm channels H2S from the volcanic ventsto the procaryotes which make food forthemselves and for the worms. An entirecommunity of crabs, starfish and mussels liveon this food supply.

PHOTOMICROGRAPH ofMETHANOGEN cells



18

The Ice-Concentration Scenario

Some scientists have doubts that theorganic chemical “soup” of the oceanscould ever have been concentratedenough in “Urey-Miller chemicals” forenough chemicals to form microspheresand eventually living cells.

Experiments show that as sea-waterfreezes, the dissolved chemicals can bepushed together into small zones ofvery high concentration.

Some scientists suggest that life beganin pools of water that periodically frozeand re-melted. Each freezing cyclecould have concentrated the chemicalsso that suitable microspheres couldform.

Perhaps life began in a place like this?Certainly, there are plenty of Archaea(and others) which can thrive in theseextreme conditions.


Other Possible Environments in Which Life BeganIt is generally assumed that the first living cells formed in the oceans of theprimitive Earth. However, the Archaea (including many types other than the

methanogens and thermoacidophiles) inhabit a huge range ofextreme environments on Earth today.

Could this mean that it was in one of these extreme environments that life firstbegan? Some scientists have suggested that this could be the case.

The Volcanic Vent Scenario

We believe that the primitive Earth of 3-4 billion years ago was a lot hotterthan today, and that volcanic activitywas very widespread.

The presence of the thermoacidophilesin modern hot springs proves that lifecan thrive in such conditions, so maybethat’s where life actually began.

The Clay Sediments ScenarioSome scientists have pointed to theimpressive catalytic properties of clayminerals called zeolites, which can attractorganic molecules and cause chemicalreactions to occur, includingpolymerisation, an essential reaction tomake the large, complex molecules of life.

They suggest that perhaps the firstliving cells began in zeolite claysediments, where the necessaryreactions of life could get some helpfrom the clay itself. This might havehappened deep in the Earth, and it isinteresting to note that some Archaeatypes are found thriving (although insmall numbers) deep in the rocks of thecrust.




19


Eucaryotic cells are those which have atrue a)............................... and otherb)............................-bound organelles.Cells lacking these features are calledc)..................................................... Thetechnology which allowed us todiscover this was thed)...................................... .......................

Other new technologies such ase)................................................... haveshown that not all procaryotes are thesame. One type, now called thef)..................................... have significantdifferences such as g).............................

We think they may be descended fromsome extremely ancient cells fromabout h)................... billion years ago.

One type are calledi)...................................... because theyproduce methane from the gasesj)......................... and k).............................They live in habitats such as in thel)....................................... under waterand in the m).............................. of manyanimals. These organisms aren)................................................. whichmeans they live without oxygen, and infact would be o)........................................by it.

Another type of Archaea are thep)............................................... whichthrive in habitats such asq)..........................................and in thedeep ocean, around r)................................................................

These organisms are s).....................-synthetic. They make food from simpleinorganic chemicals, using energy fromt).................................... (chemical name)which is common around volcanicvents. The deep-sea variety are vital totheir isolated ecosystems because theyu)...............................................................................................................

Because the Archaea are so ancient,and because they live in such extremev)..................................., it has beensuggested that perhaps life did notbegin in the w)........................................as generally assumed. Alternativeplaces for life to have started includex)............................... vents, in sedimentsof clays called y)................................... oreven in cold places where chemicalscould become z).......................................as the water froze.


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kkeeeepp iitt ssiimmppllee sscciieennccee TM

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Worksheet 5 Procaryotic Life



20


Multiple Choice1. A cell like the one shown:

A. may have lived when the Earthwas anoxic.B. may have been the first type

to appear on Earth.C. evolved from procaryotic

ancestors.D. could be a member of theArchaea.

2. The realization that the “Archaea” are verydifferent to other procaryotes has come mainlyfrom:

A. use of the electron microscope to study thecells.B. study of the extreme habitats in which theylive.C. discovery of fossil cells from 3 billion yearsago.D. study of their biochemical pathways andDNA.

3. You would be unlikely to discover“methanogen” cells living in:A. the intestines of a goat.B. the soil in your garden.C. the mud of a swamp.D. the sediments under the sea floor.

4. The group known as ‘thermoacidophiles” arebest described as:A. chemosynthetic autotrophs.B. autotrophic decomposers.C. photosynthetic heterotrophs.D. chemosynthetic eucaryotes.


5. ( 4 marks) Distinguish between procaryotic andeucaryotic cells, naming examples of each.

6. ( 5 marks)a) Identify the technology which has producedevidence that the living procaryotes includetwo fundamentally different types of life.

b) i) Identify a group of organisms belonging tothe “Archaea”.

ii) Describe the habitat of the group named inpart (i).

iii) Outline similarities between the currenthabitat of these organisms, and the Earthenvironment of the past.

7. (3 marks) It is generally assumed that life began in theoceans of the early Earth. However, there havebeen other suggestions.

Describe one possible alternative environmentin which life may have originated. Give areason why this idea is proposed as a serioushypothesis.





21

The Need to Classify Imagine a supermarket without any system for placing products on the shelves.

Baked-beans are under the light bulbs, beside the fresh tomatoes, the ice-cream and the washing detergent. This would be chaos!

Cladistic ClassificationIn recent times, the use of structural criteria isbeing improved and extended using informationfrom new technologies such as the electronmicroscope and DNA and biochemical studies.

DNA and protein sequencing is able todetermine the “relatedness” of species in anevolutionary sense. A system based more onthe evolutionary pathways is called a “CladisticClassification”.

The advantage of a cladistic system is that thegroupings are truly “family trees” that putorganisms together in groups with their truerelatives.

More and more, as fossil discoveries and thenew technologies reveal more details aboutevolutionary relationships, the traditionalMorphological classification is being adjustedand altered to become more Cladistic. Examplesof these changes will be discussed later.

4. THE VARIETY OF LIFE & HOW WE CLASSIFY IT

MORPHOLOGICAL CLASSIFICATION

BIRD isDIFFERENT

Croc & Lizard in SAME GROUP

Based on bodystructure

Croc & Bird in SAME GROUP

CLADISTIC CLASSIFICATION

Based onFossils and

DNA studies,which show evolutionary

relationships

LIZARD isDIFFERENT

The Criteria Used to ClassifyMorphological Classification

Traditionally, biological classificationuses “morphology”... the structure oforganisms’ bodies and cells to placeeach species into groups with otherswith similar structures. Using structuralcharacteristics has several advantages:

• Usually, structural features stay the samethroughout an organism’s life, unlike (say)colour which could change from time to time.

• Structural features are often obvious andeasily observed so that classification (at least at a general level) is quick and easy once youknow the things to look for.

• Structural features are often the result of evolution, so this can automatically lead to the placing of related species into the samegroups.

However, this doesn’t always work.

Example: Based on structural features, thesnakes, lizards & crocodiles are classifiedtogether as “Reptiles”, while the birds are aseparate group. See more details at right.

Taxonomy

The branch of Biology concerned withputting the living “supermarket” intoorder is called “Taxonomy”. Overseveral hundred years a system ofclassifying living things has developedin order to:

• bring order to the study of millions of living organisms.

• help communication, by agreeing on a uniquename for each species.

• show the relationships between organisms, or between groups, so that the evolutionarypathways can be more easily interpreted.

Fossils and DNA evidence suggest thatcrocodiles and birds are actually more closelyrelated than crocodiles are to snakes & lizards.




22

The Classification HierarchyA “hierarchy” means an organisation involving levels. For example, an army has a

hierarchy of command where a corporal or sergeant commands a section ofsoldiers, a lieutentant commands a platoon of sections, a captain commands a

company of platoons, and so on, upwards. As you go upwards through the levels,you are including more and more soldiers in each higher grouping.

The Biological Hierarchy works the same way:

Level or “Taxon” Example 1: Human Example 2: Eastern Grey KangarooDefining Criteria

KINGDOM Animals Animals (Eucaryotic cells, no cell wall)

PHYLUM Chordates Chordates (Animals with a notochord)Sub-PPhylum: Vertebrates Vertebrates (Chordates with spinal chord

enclosed in a vertebral column)

CLASS Mammals Mammals (“warm-bblooded”, furry, females have milk glands)

Sub-CClass: Metatheria (Marsupials... pouched mammals)

ORDER Primates Diprotodonts (Herbivorous marsupials)(mammals with graspinghands, binocular vision)

Sub-OOrder: Anthropoids (includes humans, apes & monkeys)

FAMILY Hominids Macropods (“big-ffoot” marsupials...includes all kangaroos(apes & humans) & wallabies)

GENUS Homo Macropus (includes only certain large kangaroos)(humans, including extinct ancestors & relatives)

SPECIES sapiens giganteus (Eastern Grey Kangaroo)(modern humans only)

At the top of the “taxon” hierarchy the groups are broad and general and contain many differenttypes. As you go down the hierarchy the groups become smaller until at the bottom you have

defined one specific organism... the species.

Notice that extra taxons can be added between the main levels, as needed, by using “sub-”” groups and “super-”” groups.

You need to remember that the classification system is an arbitrary, human-made, artificial scheme trying to impose some order

on the complexity and amazing variety of living things.

As we learn more, we may change the rules and adjust the system to match our improving knowledge.

The “Binomial System” of NamingTo name any species you use its Genus and species names. So a human is “Homo sapiens” and the eastern grey kangaroo is “Macropus giganteus”.

Note: the Genus name must be written with a capital letter, but the species namemust be written in lower case. The name is usually underlined and/or in italics.



23


Getting Specific: What is a Species?At the top of the classification system are the “Kingdoms” of life,

each containing many thousands of life forms.

At the bottom are the individual types, or species. A species refers to a single type of living thing which reproduces its own kind, over generations.

One species either cannot, or normally does not, interbreed with another species.

What’s in a Name?Each species has been given a scientific name which is used by all scientists.

This ensures that there is no confusion about exactly which organism is being studied or discussed, when scientists communicate.

The name of each species has 2 parts. We say it is binomial. (bi = 2, nom = name)

These 3 “big cats” are all closely related and, sure enough, their scientific namesall have the same “surname”.

Lions and tigers are closely related and(in a zoo) sometimes inter-breed. Theirbabies are called “ligers” or “tigons”.

However, in thewild these

animals nevermeet and never

inter-breed.Therefore, they are considered

separate species.

Horses and donkeys can inter-breed too.Their baby is called a “mule”.

This would probablynever happen in nature,but more importantly,mules are not fertile andcannot have babies.Horses and donkeys areconsidered separatespecies because they cannot inter-breed over generations.

Example:We might call this

animal the “easterngrey kangaroo”, but

scientifically it isMacropus giganteus

The name mustalways be underlined

or in italic print.

This red kangaroo isMacropus rufus.

Notice how the firstpart of the name is

the same?Closely related

species have thesame first-name, just

like human familymembers having the

same surname.

Leopard Paantheraa paantheris

LionPaantheraa leo

TigerPaantheraa tigris




24

Classification KeysOne of the important aids to using theclassification system is the dichotomous key.“Dichotomous” means to divide in two, so itmeans the key always splits into 2 alternativepathways. At each “decision point” twoalternative criteria allow you to choose thecorrect path to take, to eventually classify anorganism into a taxonomic group.

The criteria used need to be structural, inkeeping with the whole concept of biologicalclassification.

Dichotomous keys can be in diagram form like aflow chart, or contain a series of pairedstatements.

Paired Statements KeyAt each “level” is a pair of statements. Decide whichalternative (a or b) applies, then go to the next levelspecified, until the name of a group is given.

Level 1a) Has 2 pairs of wings .............................. level 2b) Has 1 pair of wings............................... Diptera

Level 2a) Front and hind wings have similar texture

and patterns. May be different sizes.......level 3b) Front and hind wings quite different in

thickness and/or texture .........................level 5

Level 3a) Body has distinct, narrow “waist” between

thorax and abdomen.................... Hymenopterab) No distinct “waist” ............................... level 4

Level 4a) Wings covered in patterned

scales.......................................... Lepidopterab) Wings clear, with

many veins.................................... Odonata

Level 5a) Front wings totally “hardened” forming

protective cover for rear wings.No large mouth parts....................... Coleoptera

b) Front wings only partly hardened. Large mouthparts for grasping or piercingprey ............................................ Hemiptera

insectA

insectB

insectC

insectD

insectE

insectF

START

OOnnee ppaaiirr ooff wwiinnggss

DipteraTTwwoo ppaaiirrss ooff wwiinnggss

FFrroonntt aanndd hhiinndd wwiinnggssqquuiittee ddiiffffeerreenntt iinntthhiicckknneessss aanndd//oorr

tteexxttuurree..

WWiinnggss ccoovveerreedd iinnppaatttteerrnneedd ssccaalleess

Lepidoptera

NNoo ddiissttiinncctt ““wwaaiisstt”” BBooddyy hhaass ddiissttiinncctt,,nnaarrrrooww ““wwaaiisstt”” bbeettwweeeenntthhoorraaxx aanndd aabbddoommeenn..

Hymenoptera

FFrroonntt wwiinnggss oonnllyyppaarrttllyy hhaarrddeenneedd..

LLaarrggee mmoouutthhppaarrttss ffoorrggrraassppiinngg oorr ppiieerrcciinngg

pprreeyy..

Hemiptera

FFrroonntt wwiinnggss ttoottaallllyy““hhaarrddeenneedd”” ffoorrmmiinnggpprrootteeccttiivvee ccoovveerr ffoorr

rreeaarr wwiinnggss..NNoo llaarrggee mmoouutthh ppaarrttss

Coleoptera

WWiinnggss cclleeaarr,, wwiitthhmmaannyy vveeiinnss

Odonata

FFrroonntt aanndd hhiinndd wwiinnggsshhaavvee ssiimmiillaarr tteexxttuurree

aanndd ppaatttteerrnnss.. MMaayybbee ddiiffffeerreenntt ssiizzeess..

Flow-Chart Diagram KeyChoose the correct path at each branch

Check your answers in Answer Section

WWiinngg ppaarrttllyytthhiicckkeenneedd

PPaatttteerrnneeddssccaalleess

TWO DIFFERENT TYPESOF DICHOTOMOUS KEY

(Both these keys give the same result. Try both)

Use the keys below to classify these insects

into groups (Orders)



25

The Five Kingdom SchemeIn the 20th century, the electronmicroscope revealed much morestructural detail about cells.

The ultracentrifuge allowed cell parts to beseparated for chemical analysis and the useof radio-isotopes for tracing biochemicalpathways showed up fundamentaldifferences between living things.


ANIMALSEucaryotic, multicellular,

heterotrophic, no cell wall

PLANTSEucaryotic,

multicellular,autotrophic, with cell-wwall

MONERAProcaryotic

cells

PROTISTSEucaryotic, single-ccelled.

Includes plant-llike and animal-like types such as single-ccelled

algae & protozoa

FUNGIEucaryotic, multicellular,

heterotrophic, with cell-wwall

LIVINGTHINGS

Changes to the Classification SystemThe biological classification system was developed over 200 years ago. Since thattime an enormous amount of new knowledge has been discovered which has, from

time to time, necessitated changes in the way we classify life.

Two Kingdom SchemeWhen the system was invented, all known living thingsseemed to be either plant or animal, so a “TwoKingdom” scheme was used. The fungi appeared to berather weird plants, and later when bacteria werediscovered, it was decided that they were closer toplants than animals.

LIVING THINGS

ANIMALS PLANTSIncluding Includes fungi &single-ccelled bacteria, as well protozoa as single-ccelled

algaeBy the middle of the 20th century it was realised that

this scheme was really not satisfactory.

Scientists realised:

• the enormous difference between procaryotic and eucaryotic cells.

• that the fungi are not just weirdplants... they’re a totally different type of organism.

• that single-celled organisms arefundamentally different to multicellular life, regardless of other characteristics.

This new understanding led to adoptionof a new scheme with Five Kingdoms.

More Changes in the Future?The new technologies of DNA and proteinsequencing have already revealed thefundamental differences between the Archaeaand the other types of procaryotes.

Because of this, many scientists are alreadyusing a Six Kingdom Scheme:

ARCHAEA ANIMALS PROTISTS

FUNGIBACTERIA PLANTS

However, this method is not Cladisticenough for others... it doesn’t showclearly enough the evolutionaryrelationships between the major groups.To do so, some scientists are beginningto use another taxon, called “Domain”which is higher than “Kingdom”.

Perhaps in the future we will use a newscheme something like that shown onthe next page...



26

The Problems of Classifying Extinct Species

Our biological classification scheme isused not just for today’s living things,but for all the extinct species we knowfrom fossils.

There are problems classifying anorganism from its fossils alone:

• modern classification relies on cell structures at some taxons. In most fossil imprints the cell details have not been preserved.

• the new DNA technologies and biochemical analysis which are souseful for finding “relatedness” amongliving organisms, cannot be used onmost fossils because the organicchemicals have not been preserved infossilisation.

For a fossil such as that shown above, there isno problem classifying it. An expert in fishanatomy can probably decide on its groupingsall the way down to Genus, and even assign it aspecies name.

For other fossils though, especially if they arevery small and very ancient, exact classificationis impossible without DNA samples and well-preserved cellular imprints.

Clear cellular imprints are very rare, and DNAsamples do not survive fossilisation, except in afew rare cases of animals being preserved byfreezing for a few thousand years, but not formillions of years. The “Jurassic Park” scenarioof re-building dinosaurs from fossilised DNAcannot really happen.


This is a life-size sketch of “Hallucigenia”, abizarre animal whose fossils are known from

the famous Burgess Shale deposit in western Canada.

It lived over 500 million years ago. Althoughvaguely related to insects, its 7-part body plan

defies modern classification.

Until the exact details are agreedupon, we will continue to use the

5 (or 6) Kingdom Scheme

The Next Classification Scheme?Three Domains

Domainsof Life

Sub-DomainsorSuper-Kingdoms

Kingdoms

LIVINGTHINGS

BACTERIA EUCARYOTESARCHAEA

ANIMALS

PROTISTSsingle-ccelled

METACYTESmulticellular

PLANTS FUNGI

Classify This!




27

Worksheet 7Fill in the blank spaces.

The branch of Biology which dealswith classification is calleda).........................................

Some reasons for classifying are;• to bring some b)..................................

to the chaos.• to help c).............................................

by giving uniformity of names.• to help the study of life by placingorganisms in groups which havesimilar d)................................• to show how organisms aree).............................. in an evolutionarysense.

The criteria used to classifyorganisms are usually f)........................features, because these do notusually g)........................... during anorganism’s life. Also, structures areusually the result of h)...........................Classification based on structuralfeatures is called ai)..................................... classification,while a “Cladistic” scheme is basedon j).......................... relationships.Modern technologies, especiallyk).......................... and l)........................sequencing are useful in determining“relatedness” for Cladistic schemes.

The classification hierarchy has 7main levels, or m)............................. The most general level is “Kingdom”,then come n)............................,o)..............................., “Order”,p)........................., q).............................and finally r)............................ Extrataxons can be added between themain levels using prefixes(s)................ (below) and t)..................(above).

ClassificationTo name a species, you use theu).................... and v)...........................names. If 2 species have the samegenus name they must be veryw)............................................................

The definition of a species is basedon x)........................, so if 2 organismsnaturally produce y)..................... &............................ offspring then theyare the same species.

Classification keys are alwaysz)................................ which means tosplit in two.

The classification system is arbitraryand subject to changes. For example,originally a 2 kingdom system wasused because everything wasthought to be either aa)........................or ab)............................... In the 20thcentury, improved knowledgeresulted in a switch to a 5-kingdomscheme: as well as plants andanimals there were the kingdoms of ac).........................., (which areprocaryotic), ad).............................(single-celled eucaryotes) andae)................................................

It is likely that this will change againin the future, since it is alreadyrecognized that the kingdom“Monera” should be split intoaf)...................... and ag).......................

Dichotomous Key Exercise

Use the information given on page 25about the “Five Kingdoms” of livingthings to construct a dichotomouskey.




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Multiple Choice1. If you were to study an extensive fossildeposit, and work your way down through thelayers, you might expect the fossils to show atrend:A. of increasing complexity.B. of greater resemblance to modern life.C. of decreasing diversity.D. of younger and younger ages.

2. Of the following “taxons” which one is themost general grouping, or least specific?A. FamilyB. PhylumC. ClassD. Genus

3. A particular animal’s scientific name is Mushirsutus. Which of the following animals ismost closely related ?A. Mus rufusB. Volex hirsutusC. Hirsutus ascaraD. Hirsutus muscus

4. In the “5-kingdom” classification scheme, if anorganism was described as “eucaryotic,heterotrophic and multicellular”, it couldbelong to either of TWO groups:A. plants or protists.B. fungi or monera.C. animals or moneraD. animals or fungi.

5. If we were to adopt a “SIX kingdom” schemefor classification, the existing kindom thatwould have to be split up is the:A. Protists.B. Fungi.C. Monera.D. Plants.

6. The problem with classifying some extinctorganisms from their fossils is that:A. we cannot be sure what habitat they lived in.B. their cell structure & DNA are not preserved.C. only hard parts, such as bones, shells, etcare preserved.D. their original body parts have been“petrified”.

Longer Response QuestionsMark values given are suggestions only, and areto give you an idea of how detailed an answer isappropriate.

7. (3 marks) Give 3 reasons to justify the existence of abiological classification system.

8. (6 marks) Compare and contrast a Morphological to aCladistic classification scheme and give anadvantage of each.

9. (2 marks) The horse and the donkey both belong thegenus Equus. They can interbreed producinghealthy offspring known as a “mule”. Mules aresterile and cannot produce offspring.

Should the horse and donkey be considered asmembers of the same, or separate, species?Explain your answer.

10. (5 marks) Use the following list of characteristics toconstruct a dichotomous key for the majorplant groups.

Group True Veins? Seeds? SeedLeaves? Structure

Algae No No No n/aMosses Yes No No n/a

(simple)Ferns Yes Yes No n/a -Conifers Yes Yes Yes conesAngiosperms Yes Yes Yes flowers/fruits

11. (5 marks) Discuss, with reference to the “2-kingdom” andthe “5-kingdom” schemes, the impact ofchanges in technology on biologicalclassification schemes.





29

CONCEPT DIAGRAM (“Mind Map”) OF TOPICSome students find that memorising the OUTLINE of a topic

helps them learn and remember the concepts and important facts. Practise on this blank version.

LIFEon

EARTH




30

Answer SectionWorksheet 1a),b)& c) any 3 of carbon dioxide, methane,ammonia, hydrogen, nitrogen, water vapour.d) oxygen e) volcanoesf) lightning g) ultra-violet (UV)h) organic i) Urey & Millerj) & k) sugars & amino acids (organic molecules)l) outer space m) radiationn) isotopes o) halfp) fossils q) related

Worksheet 21. B 2. D 3. A 4. A5. a) There would have been a lot of volcanicactivity, constantly adding volcanic gases to theatmosphere. Violent storms would have beennear continuous, with a lot of lightning.. Withoutan ozone layer, there would have been highlevels of UV radiation from the Sun penetratingto the surface.b) The atmosphere would have contained nooxygen at all, but been made up of gases suchas carbon dioxide, nitrogen, ammonia,methane, hydrogen and water vapour.

6.a) The experiment was designed to test thehypothesis that the conditions of the primitiveEarth could have naturally produced organicmolecules.b) Flasks were set up containing the simpleinorganic chemicals thought to be present onthe primitive Earth. The flasks were heated,irradiated with UV, and electric sparkssimulated lightning..After several weeks, the flask contents wereanalysed chemically.c) the flasks were found to contain organicchemicals including sugars and amino acids.d) Conclusion: the hypothesis is supported.Organic molecules can be produced fromsimple inorganic chemicals under theconditions thought to have existed on Earth 4BYA.

7.a) Because radio-isotopes “decay”, theirradiation levels decline in a predictable way.This allows rocks & fossils to be accurately“dated”. Thus we have an accurate time scalefor the history of the Earth & its life.b) DNA sequencing. This can determinesimilarities & differences in the DNA of differentspecies and is a measure of how closely relatedthey are in an evolutionary sense.

Worksheet 3a) 4.6 BYA b) organicc) hydrophobic d) microspherese) membranef) copy/duplicate/replicateg) 3.5 to 4 BYA h) anaerobici) organic j) autotrophsk) chemicals l) cyanobacteriam) stromatolites n) oxygeno) iron p) banded ironstoneq) anoxic r) cellular respirations) ATP t) eucaryoticu) Endosymbiosis v) digestw)chloroplast x) DNA & ribosomesy) sexual reproductionz) geneticaa) speeded up ab) multicellularac) algae ad) spongesae) hard

Worksheet 41. C 2. B 3. D 4. C 5. A 6. C

7.1. Production of organic molecules, which arethe building blocks of living cells.2. Formation of “microspheres” from fatty lipidmolecules. These act like membranes...necessary to form the first cells.

8.a) The change from an environment withoutany free oxygen gas (anoxic), to one with freeoxygen (oxic).b) The cyanobacteria, carrying outphotosynthesis, released the oxygen.c) When the Earth became oxic, many of thepreviously dominant anaerobic organismsbecame extinct, and it opened up opportunitiesfor the evolution of cells using aerobic cellularrespiration.

9. a) Explains the evolution of the eucaryotic cellsfrom procaryotic ancestors.b) A larger procaryotic cell “ate” a smaller one,but failed to digest it. The small cell survivedinside the larger one, and evolved to becomean “organelle” such as mitochondrion orchloroplast.c) Mitochondria and chloroplasts contain theirown DNA and it is bacterial-type. This suggeststhese organelles were once separateprocaryotic cells.



31

Worksheet 5a) nucleus b) membranec) procaryotic d) electron microscopee) DNA sequencing / biochemical pathways /protein sequencingf) Archaeag) RNA / cell walls / enzymesh) 2 to 3 BYA i) methanogensj) & k) carbon dioxide & hydrogenl) mud / sediments m) gut / intestinesn) anaerobic o) poisoned / killedp) thermoacidophiles q) volcanic hot springsr) volcanic vents s) chemo-t) hydrogen sulfide u) produce all the foodv) habitats w) oceanx) volcanic y) zeolitesz) concentrated

Worksheet 61. C 2. D 3. B 4. A

5.Eucaryotic cells have a “true nucleus” andother membrane-bound organelles. Examplesinclude all plants & animals.Procaryotic cells lack organelles, except non-membrane structures such as ribosomes. Theyhave a “nuclear region” but no true nucleus.Examples are the bacteria, cyanobacteria andthe Archaea.

6.a) Evidence for this has come from study ofbiochemical pathways, protein, DNA & RNAsequencing, and chemical analysis of cell partssuch as cell walls. This has shown that the“mainstream” procaryotes (e.g. bacteria) aredistinctly different to the Archaea.b) i) Methanogens

ii) Anaerobic muddy sediments underswamps, wetlands, oceans.

iii) Their current habitats may be similar tothose they occupied 3 BYA... i.e. anaerobic,lots of organic molecules available.

7. Life may have originated in zeolite claysediments. Zeolites have a chemical ability toattract organic molecules and to catalyzechemical reactions such as polymerization,which is essential for life to get started.

Classification Keys Exercise page 24

Insect A = Coleoptera Insect B = LepidopteraC = Hymenoptera D = DipteraE = Odonata F = Hemiptera

Worksheet 7a) Taxonomy b)order / organizationc) communication d) similar characteristicse) related f) structuralg) change h) evolutioni) Morphological j) evolutionaryk) DNA l) proteinm) taxons n) Phylumo) Class p) Familyq) Genus r) Speciess) sub- t) super-u) Genus v) speciesw) closely related / similarx) reproduction y) healthy & fertilez) dichotomousaa) & ab) Plant or animalac) Monera ad) Protistsae) Fungiaf) & ag) Bacteria & Archaea

Make a Dichotomous Key Exercise There are many correct ways to do this. Format may be “Paired Statements” or“Flowchart Diagram”. A Good key will use onlystructural characteristics and it will beunambiguous, and (most importantly) it WILLWORK when used.

Sample Answer:1. a) Cells are Procaryotic ..................... Monera

b) Cells are Eucaryotic ....................... level 2

2. a) Organism is single-celled ............ Protistb) Multicellular .................................... level 3

3. a) Cells have chloroplasts(photosynthetic)....... Plant

b) Cells lack chloroplasts ...................... level 4

4. a) Cells have a cell wall ...................... Fungib) No cell wall .................................... Animal




32

Worksheet 81. C 2. B 3. A 4. D 5. C 6. B

7Classification:1. brings some order and organization to thechaos of millions of different species.2. helps communication by giving everyspecies a unique name agreed by all.3. places organisms into groups of similartypes, making it easier to understandevolutionary relationships.

8. Both classification schemes place organismsinto similar groups, and try to show therelationships between them.

Morphological systems used cell & bodystructures as their criteria. This has theadvantage of being relatively easy to study andobserve.

Cladistic systems attempt to place organismsinto groups according to their evolutionary“relatedness”. This has the advantage ofproducing true “family trees” that help usunderstand the history and evolution of life.

9.They must be considered as separate species.

The definition of a species is that 2 organismsare the same species if they can interbreed andproduce healthy, fertile offspring. Since themule is sterile, the conditions of the definitionare NOT met, so horse & donkey are not thesame species.

10. (Many correct answers possible)

1. a) Do NOT have veins........................... level 2b) Have veins ....................................... level 3

2. a) Have simple leaves ...................... Mossesb) No leaves ....................................... Algae

3. a) Produce seeds ................................ level 4b) Do not produce seeds ...................... Ferns

4. a) Seeds produced in cones ............ Conifersb) Seeds produced in

flowers/fruits.......................... Angiosperms

11. When the classification scheme was firstdeveloped it seemed that all life was eitherplant or animal, so a 2-kingdom system wasused.

Later technologies, especially the electronmicroscope which revealed details of cellstructures led to the realisation that :• there are 2 totally different cell types...

procaryotes & eucaryotes.• the Fungi are not plants, but a totally differentlife form.• unicellular organisms are fundamentallydifferent to multicellular, regardless of beingplant-like or animal-like at the cell level.

The result was a change to the 5-kingdomsystem, recognising Animals, Plants, Fungi,Protists & Monera as being fundamentallydifferent.


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