kiss notes life on earth

keep it simple science TM

www.keepitsimplescience.com.auPreliminary Biology Topic 3copyright © 2005-2007 keep it simple science

St Josephs Catholic College SL#804465

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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...The Concept of Biological Evolution“Evolution” means to undergo a sequence ofchanges. The change is NOT random... it follows asequence or pattern.

There is overwhelming scientific evidence that LIFE ON EARTH HAS CHANGED

over millions of years, and that there is a definitepattern in the changes... life has evolved.

In this topic you will study the FACTS OF EVOLUTION

...what we know about the pattern of changes to lifeon Earth over millions of years.

In a later topics you will study the THEORY OF EVOLUTION

...the scientific theory which attempts to explain howand why evolution of life occurs.

The Variety of Life on EarthEstimates vary enormously, but there areundoubtably millions of different types (species) ofliving things on Earth today. This variety is just a tinyfraction of all the different types that have ever lived.

How can we study and understand such diversity?Only by developing a system to classify organismsinto groups.

You already know about grouping like-thingstogether:

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

Preliminary Biology Topic 3

LIFE ON EARTH

Plants aredifferent toanimals...

whales are exactlyunlike worms...

jellyfish are not likespiders...

and somethings are

simplyunique.

Photo by Diana




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The EarlyEarth

Technologiesthat help usUnderstand

Changing Ideas

Science &

Culture

The Need to Classify&

Criteria used

DichotomousKeys

The Classification Systemkingdomphylumclassorderfamilygenus

species

Changesto the

System?

Technolgiesto Study

Procaryotes

Other PossibleEnvironments inWhich Life Began

Time-LLine ofthe Main Steps

•molecules•membranes•cells•autotrophes•eucaryotes•multicellular

organisms

The Urey-MillerExperiment

MethanogensThermoacidophiles

Life from OuterSpace Theory

LLIIFFEEoonn

EEAARRTTHH

Originsof

Life on EarthHistory

ofLife on Earth

ProcaryoticOrganisms

Today

Variety of Life&

How We Classify

CONCEPT DIAGRAM (“Mind Map”) OF TOPICSome students find that memorizing the OUTLINE of a topic helps them learn and remember the concepts andimportant facts. As you proceed through the topic, come back to this page regularly to see how each bit fits thewhole. At the end of the notes you will find a blank version of this “Mind Map” to practise on.

The Archaea

Theoriesof

Origins of Life




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

The Earth of 4 billion years ago was very different to thatof today:-

How do we know that? We cannot be 100% sure, but thisdescription matches with:-• conditions and chemicals on other planets in the Solar

System that our telescopes and space probes have studied• the chemicals that erupt from volcanic vents today, and

probably always have.

Spontaneous Generation of LifeIn ancient times and throughout history until about 150years ago, it was generally believed that life could appearspontaneously... maggots just “happened” in rotting meat,mice would “appear” in a pile of old clothes, and frogs just“arise” from swampy ground.

This concept was finally proven wrong by Louise Pasteur’sfamous experiment of 1862...

...and by the 1880’s the cell theory of life was established asa scientific principle. (see Topic 2 “Patterns in Nature”)This includes the statement that “all cells (life) come(s)from pre-existing cells (life)”.

So how did the first living thing get started on the primitive Earth?

Chemicals First, Then CellsThe chemicals present in the atmosphere of the primitiveEarth contained exactly the same chemical elements thatthe organic chemicals of life are made from... mainlycarbon, hydrogen, oxygen & nitrogen.

In the 1920’s it was suggested by two scientistsindependently, that maybe the conditions on Earth 4 billionyears ago:-• firstly caused chemical reactions that made complex

organic molecules• then these chemicals somehow came together to form a

living organism• and once life got started, it evolved into all the species we

see in the fossil record and those alive today.

The Urey-Miller Experimentwas designed in the 1950’s to test the first part of thishypothesis... that the conditions of the primitive Earthcould spontaneously produce the complex organicmolecules necessary for life to start.

The initial experiments resulted in the production of sugarsand amino acids, and later variations produced the chemicalbuilding blocks for cell membranes, and even for DNA.

THIS SUPPORTS THE FIRST PART OF THEHYPOTHESIS... the chemicals of life could haveappeared spontaneously on the primitive Earth.

1. THE ORIGINS OF LIFE ON EARTH

VVoollccaannooeess addmany gases toatmosphere

Violent storms - a lot ofLLiigghhttnniinngg UU..VV.. rays

from Sun

Early oceans

AAttmmoosspphheerree ooff HH2OOvvaappoouurr,, mmeetthhaannee,,aammmmoonniiaa,, ccaarrbboonnddiiooxxiiddee,, nniittrrooggeenn,,

hhyyddrrooggeenn..NNOO ffrreeee ooxxyyggeenn

Each flask contains a “broth”,boiled until sterilized

Closed flaskremains

sterile... nomicrobesgrow in it.

Open flask growsmicrobes & rots.It was believedthe life came

spontaneouslyfrom contact

with air.

This flask is open to theair, but the “gooseneck”prevents airborne spores

getting to the broth.It remained sterile, andproved “spontaneousgeneration” is wrong.

“Ocean”Flaskbeganwithpurewater

“Atmosphere”Flask

HHEEAATT

Vapo

urs

circ

ulat

e

Electric sparksimulateslightning

Condenser coolsvapours back to

liquids

“Liquid Trap”was later found to

contain organicchemicals, such assugars and aminoacids... the basicchemicals of life.

Mixture of gases to simulateprimitive atmosphere.methane(CH4), CO2,

ammonia (NH3), N2, H2




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Significance of the Urey-Miller Experiment1. It demonstrates the way Science works, by formulatingan hypothesis and then testing it by experiment. In this casethe hypothesis was put forward by other scientists 30 yearsbefore the experiment was done.

2. Although it didn’t prove how life got started on Earth,the experiment’s results support the hypothesis by showingthat life-forming chemicals could have been producednaturally under the conditions of the primitive Earth.

3. In combination with evidence fromSpace ExplorationVulcanology & Earth ChemistryAncient Rocks & FossilsStudy of “Primitive” Life-Forms Alive Todayand others...

the Urey-Miller experiment is just one part of a “package”of evidence that seems quite consistent with the idea thatlife formed naturally on the primitive Earth some 4 billionyears ago, and has evolved into what we see today.

We cannot yet prove how life arose, but the weight ofevidence suggests we’re on the right track.

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 (or at least the chemicals theyformed from) could have come from outer space.

The evidence for this is:• carbon compounds have been detected in many parts ofthe Universe... interstellar gas clouds, meteorites & comets

• a meteorite or comet collision with a planet can throwfragments into space, and theoretically could carry livingcells to another planet.

Technologies That Help Us Understand There are certain technologies that have helped scientists toput together the whole “package” of knowledge about theorigins and evolution of life.

Radiometric DatingThe atoms of each chemical element are not all exactly thesame. They have the same number of protons & electrons(that’s what makes them that element), but the number ofneutrons in the atom may vary. Such atoms of the sameelement, but with a different number of neutrons, arecalled “isotopes”. Some isotopes are “radio-active” and giveoff nuclear radiations... hence “radio-isotopes”.

Radio-isotopes “decay” at a predictable rate. That is, thelevel of radiation dies down over time in an exactmathematical way.

By measuring the amount of radiation present now, andknowing the “half-life” of the isotope, the age of objectscan be calculated.

The most famous example is “Carbon Dating” which usesan isotope of carbon (called “carbon-14”) to find the ageof artifacts from human history.

Carbon-14 has a half-life of about 5,700 years, so if a boneor wooden tool is measured to have only 1/2 as muchradiation as it would have had originally, then one half-lifehas gone by since that bone or tree died... therefore, it mustbe 5,700 years old.

Carbon-14 is not much use beyond about 40,000 years, butthere are other isotopes (e.g. potassium and uranium) withhalf-lives of millions of years which can determine the agesof fossils and rocks which formed millions, or even billionsof years ago.

TIME

RRAADD

IIAATTII

OONN

LLEEVVEE

LL

from here

to h

ere

to here

This “Radiometric Dating” is how we know theage of the Earth, of different fossils etc, and candescribe the entire history of life on Earth with

fairly good accuracy.SSuunn

Mercury

Venus

Saturn

Jupiter

Mars

Earth & Moon

Otherstars?

This is an interesting idea, but so far the weight ofevidence supports the hypothesis that Earth life arose onEarth, and not somewhere else.

Organicchemicals are

common in theUniverse...

did life cometo Earth fromsomewhere

else?Otherplanets?

100

50

25

0

half-lifehalf-life half-life

The time it takesfor the radiationto drop to half

the previous levelis constant:

the“Half-llife”




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The Electron Microscopewas mentioned in Topic 2 as having a major impact on ourunderstanding of cells and cell structures.

Electron microscopes can also allow scientists to study veryancient fossil cells in rocks and to make comparisons withsome types of “primitive” cells which still live today. Thisgives us further clues about how ancient life-forms livedand evolved.

Biochemical Analysis & DNA TechnologyIt’s well known from TV crime dramas that by analysingtraces of DNA from a crime scene, a criminal can bepositively identified.

The technique is also used to identify the remains ofvictims of war or natural disasters such as the Asiantsunami of Boxing Day 2004. By comparing DNA samplesfrom a body part with samples from the relatives ofmissing people, scientists can positively determine whichfamily the victim is from.

The same technique can be used to find the “relatedness”of different living things, and even give estimates of howlong ago 2 related species divided from each other, in anevolutionary sense.

For example, DNA studies suggest (very strongly, to thepoint of certainty) that humans and chimpanzees areclosely related (our DNA is 99% identical) and that ourancestors and chimp ancestors diverged only about 5million years ago. We’re pretty certain about this, eventhough the relevant fossils have not been discovered.

More generally, biochemistry and DNA studies haveshown:• all life forms on Earth are related. This means that all

living things today evolved from one original type.• which types are more closely, or more distantly, related.

This complements the evidence of the fossil record, to give us a clearer picture of the exact sequence ofevolution.

Worksheet 1

Fill in the blank spaces.Check your answers in the “Answer Section” at the back.

We believe that the Earth of 4 billion years ago had anatmosphere containing gases such as (a)..................................(b)........................................ and (c)..............................................but no uncombined (d).......................................................There were many (e)........................................... erupting, andviolent storms producing a lot of (f)........................................(g)......................... radiation from the sun was at high levels.

Under these conditions, it is possible that complex (h)....................................... chemicals could form naturally.The (i)................................&.................................... experimentsupported this hypothesis. The experiment involvedsimulating the conditions of the primitive Earth, and aftersome time it was found that (j)...................................................and (k)............................................................... had formedfrom simple inorganic ingredients.

Another hypothesis for how life began on Earth is thatliving cells, or at least the chemicals they formed fromcame from (l)............................................................................

Radio-metric dating is a technique which measures the (m)................................................. from radio-active(n)...................................................................The age of rock or fossil etc can be calculated from the (o)....................-life of the isotope.

The electron microscope has not only helped ourunderstanding of living cells, but also helps us discoverand study ancient (p)................................................. in rocks.

DNA technology adds to our understanding of theevolution of life by determining how closely(q)........................................................ different organismsare.

WHEN COMPLETED, WORKSHEETS BECOME SECTION SUMMARIES

Photo by Jeremy Henderson




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Summary of the Main EventsThe following time-line identifies the major stages in theevolution of life on Earth. The main evidence for this hascome from fossils preserved in sedimentary rocks. Thetimes suggested are approximate, but based on radio-metric studies of the rocks.

Formation of Organic Moleculesprobably began as soon as the Earth was cool enough

for the molecules to exist without being torn apart again.The Urey-Miller experiment (and many others since) provethat sugars, amino acids, lipids and even the building blocksof DNA and RNA could form spontaneously in thechemical conditions of the primitive Earth.

Eventually, by 4 billion years ago, the early oceans musthave become a chemical “soup”, highly concentrated inorganic molecules.

Molecules Formed MembranesIt is thought that the next crucial step to occur was the

formation of membranes. In the watery environment ofthe oceans, hydrophobic (=“water-hating”) moleculesnaturally tend to cling together, like oil forming droplets inwater. Experiments have shown that some lipid moleculesin water will, quite naturally, form “microspheres” withother chemicals trapped inside.

A microsphere is not a living cell, but scientists believe thatstructures like this were the precursors of cells.

The First Living Cellsmust have been microspheres which trapped inside

themselves a mixture of chemicals that could attractother molecules in through the “membrane” so theybecame bigger (i.e. feeding & growing) and also causecopies of their own molecules to be built... small RNAmolecules can do this. Eventually the sphere would split intwo, (reproduction!) each part with a share of the essentialchemicals to make it all happen over again.

We can’t be sure when this happened, but by about 3.5 billion years ago we find microscopic cell-like fossils insome rocks, and by 3 billion years ago there are many fossilsof bacteria-like cells, in various forms... they were evolvinginto new types already.

These cells lived without oxygen (“anaerobic”) and wereprobably feeding on the “soup” of organic molecules stillin the oceans.

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-Millerexperiment?

Molecules formedmembranes?

Earliest known cell-likefossils

First living thingssomewhere here (?)

Throughout this immense periodall life was bacteria-like,

anaerobic (living without oxygen)and heterotrophic, feeding on the

organic molecules of theenvironment.

First autotrophs...chemosynthetic bacteria

First Cyanobacteria, usingchlorophyll for photosynthesis

and releasing ooxxyyggeenn

Over this time the Earth went frombeing AANNOOXXIICC to OOXXIICC..

Organisms using oxygen forcceelllluullaarr rreessppiirraattiioonn appeared.

First EEuuccaarryyoottiicc cells(with membrane-based

organelles)

First sexual reproduction.Evolution speeds up

Animals with hard parts (shells etc)appear. Huge increase in fossils

FishAmphibians, InsectsReptiles, MammalsDinosaursBirdsHumans

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11

33

44

55

77

88

99

66

22

22

33

One lipid moleculeLLiippiidd mmoolleeccuulleess cclliinnggttooggeetthheerr,, ffoorrmmiinngg aa““mmiiccrroosspphheerree””

Other chemicalsmay be

trapped inside

FFiirrsstt mmuullttiicceelllluullaarr ppllaannttss ((aallggaaee))aanndd aanniimmaallss

((ssppoonnggeess,, wwoorrmmss,, jjeellllyyffiisshh))

Preliminary Biology Topic 3copyright © 2005-2007 keep it simple science


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A Billion Years of ScavengingFor perhaps 1,000 million years the most advanced

organisms on Earth were bacteria-like cells which livedwithout oxygen, and scavenged the organic “soup” oforganic molecules in the oceans. Probably the productionof organic molecules (“food”) was still occurring as in theUrey-Miller experiment, but the whole regime was about tochange...

The First AutotrophsChemosynthesis & Photosynthesis

About 2.8 billion years ago, a new type of bacteria appearsin the fossil record. The fossils appear similar toautotrophic bacteria alive today, which make their ownfood, using energy from chemicals in the environment.This process is called “Chemosynthesis”. (details later)

By 2.3 billion years ago, fossils of cells recognisable ascyanobacteria appeared. These are bacterial type cells, butuse chlorophyll to trap sunlight, and produce OXYGEN astheir waste product. The cyanobacteria grew in shallowseas in structures called “stromatolites” which we find ascommon fossils in rocks from this time.(Living stromatolites still grow in some places today)

The World Goes OxicUp until this time the Earth was “anoxic”... completely

without any uncombined molecular oxygen (O2). Therewere plently of oxygen atoms of course, but they were allchemically combined in water (H2O) and various othercompounds.

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

We find huge deposits of evidence for what happenednext... the world went rusty!

In many parts of the world (including Western Australia)we find huge deposits of “Banded Ironstone”; rockcontaining layers of iron oxide (Fe2O3). The iron mineral isvery fine grained as if precipitated from a water solution.

The explanation is that, in the anoxic early conditions a lotof iron was dissolved in the oceans in the soluble form ofFe2+ ions. As the cyanobacteria began releasing vastquantities of O2 oxygen, it reacted with the iron formingthe insoluble Fe2O3 iron oxide (which is RUST).

Eventually, after about 200 milion years, all the iron wasprecipitated, and now the oxygen began building up in theatmosphere... the air became “OXIC”. This had foursignificant consequences:-

1. The natural production of organic chemicals by the“Urey-Miller process” stopped forever. Oxygen ischemically active enough to destroy organic molecules asfast as they could form.Life could never again start up the way it once did.

2. The old-type anaerobic bacteria found oxygenpoisonous, so many became extinct. A few survived inenvironments where there is no oxygen, and there they liveto this day... you will study them soon.

3. Atmospheric oxygen allowed development of an ozonelayer. This absorbs UV rays and was vital for the laterdevelopment of life on land.

4. The oxic environment encouraged a new, more efficientway to use food energy... cellular respiration. By 2 billionyears ago the familiar modern cycle was operating:

ATP is the energy compound which powers all lifeprocesses... cell division, moving, growing etc.

www.keepitsimplescience.com.au

44

66

55

WATER + CARBON GLUCOSE + OXYGENDIOXIDE

6H22O + 6CO22 C66H1122O66 + 6O22

chlorophyll

light energy

Light energy

GLUCOSE+

OXYGEN

CARBONDIOXIDE

+WATER

ATP

PHOTOSYNTHESIS(in cyanobacteria)

AEROBICRESPIRATION(in all living

things)

Living mat of cells in thintop layer

Column grows likea stalagmite. Newlayers grow on topof old, deadlayers




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The First Eucaryotic CellsAll the “more advanced” living things on Earth today

are characterized by cells containing many organelles whichare built from and/or surrounded by membranes.(This was dealt with fully in Topic 2) Such cells are called“eucaryotic”.

Prior to about 1.5 billion years ago, all life on Earth was“procaryotic” meaning that the cells lack a true nucleus,mitochondria, chloroplasts, etc. The living procaryotes oftoday are the bacteria and cyanobacteria. Without trueorganelles to organize their cell functions better, theprocaryotes have to remain very tiny, single cells in whichdiffusion distances are small, and the SA/Vol ratio is high.

And that’s how life on Earth might have remained forever,except some cells ate some smaller cells, but failed to digestthem. The small cells lived on inside their “host” in arelationship that soon became mutualism, and aftermillions of years, the ingested cells evolved to became“organelles” of the larger cell.

What’s the evidence for this?

• Both mitochondria & chloroplasts contain their own DNA, and it is bacteria-like DNA in a loop. These organelles reproduce independently of the rest of the cellin a mini-version of a cell division

• Mitochondria contain their own ribosomes for making their own proteins

• Mitochondrial enzymes (control cellular respiration) are attached to the inner membrane in a very bacteria-likeway.

This idea is known as the “Endosymbiotic Hypothesis”and is our best explanation of where the first cells camefrom that later evolved into the plants 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 producesidentical daughter cells. (as covered in Topic 2) The onlyway a new variation could occur was by occasional genetic“accidents” ... mutations. So the evolution of new typeswas very slow.

A little over 1 billion years ago, some cells beganexchanging bits of DNA with each other. Fossils have beendiscovered (using the electron microscope) of 2 cells joinedby a thin tube apparently in “conjugation”, in which thecells swap DNA fragments in a kind of simple sexualfertilization of each other.

The result is more genetic variations and more differencesbetween individuals. Evolution had more opportunities,and sure enough, the fossil record shows an acceleratingincrease in new, more complex forms appearing.

The First Multicellular Organismsappeared about 800 million years ago.

It is often an advantage for an organism to be large. Alarger organism deters predators and gathers more of theresources of the environment, so its chance to survive andthrive is better. But, as you know from Topic 2, a single cellcannot grow too large because the SA/Vol ratio gets less.

The other way to get large is have more cells.

About 800 million years ago some eucaryotic,photosynthetic cells became “colonial”. When the cellsdivided, they didn’t separate, but stayed attached to eachother, forming filaments or flat sheets. These simple,multicellular associations evolved into the algae group andfrom one type of them, came (eventually) the plants.

Similarly, some eucaryotic, heterotrophs became colonial toevolve into the first multicellular animals, similar to modernsponges. Later came flatworms and jellyfish-like creatureswith very simple body plans.

About 600 million years ago there came an “explosion” oflife. We find a huge increase in fossil numbers and forms,partly because some types developed shells and other hardbody parts that fossilized well.


99

8877

Larger cell enveloping a smaller cell forfood, but fails to digest it.Smaller cell becomes mmiittoocchhoonnddrriioonnwithin the “host” cell

By a similar process, aphotosynthetic cell is

“eaten” and becomes a chloroplast

Evolves to becomean AAnniimmaall cell

Evolves to becomea PPllaanntt cell

CELLS in CONJUGATION

Small fragments of DNA arepassed through the tube,

increasing the geneticvariations within a population




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Changing Ideas About the History of LifeFossils have been known and collected by people forthousands of years. In China they were considered as“Dragon Bones”, while it was supposed by Europeans upuntil the 1860’s that fossils represented the many types ofanimal which never made it to Noah’s Ark and so drownedin the Biblical Flood.

The “Principle of Superposition” was developed by earlyGeologists and used to start putting fossil discoveries intorelative time order, although the actual ages were not known.

Once this rough order of age for fossils was established,scientists began to see the pattern... the fossil record showsa clear sequence over time...

It was partly this pattern in the fossil record that convincedCharles Darwin that life on Earth had changed andevolved.

The fossils don’t just show that life on Earth has changed,but that is has changed in a sequence, in a direction from“few & simple” to “more variety & more complex”.

Until the 20th century, little notice was taken of the mostancient rocks on Earth, from the “Pre-cambrian” time. Fewfossils could be detected in them, and it seemed that animallife had simply appeared in abundance at a certain point intime.

Improved technologies changed all that...

Radio-metric dating of meteorites and Moon-rock told usthe true age of the Solar System and therefore of theEarth. Dating of fossils and the ancient rocks put thesequence of the fossil record into a proper time-scale.

Improved microscopic techniques, especially the electronmicroscope, discovered the cellular fossils in the ancientrocks. It was previously thought there were no traces of lifein the “Pre-cambrian” rocks.

Now with the insights into evolution provided by DNAtechnology, and the biochemical experiments of Urey &Miller and many others, we can understand the fossil recordand the history of life right back to its origins with somedegree of scientific confidence. We can’t know everything,but no longer believe in “dragon bones”.

Science Clashes With Culture?Darwin’s Theory of Evolution caused tremendouscontroversy when published in 1861 because it was notconsistent with the Biblical story of “divine creation” andmany people saw this as an attack on their religion and theirculture.

Even today, there are some religious groups who reject theentire concept of the “Evolution of Life” because theyinterpret their traditional, cultural or religious stories ofcreation very literally.

Most mainstream religions however, accept that Science isnot trying to attack any belief, culture or tradition, but onlyto understand and explain the natural world. Most religiousorganizations now accept the “Facts of Evolution” that lifeon Earth has existed for billions of years, and hasundergone progressive change.

Many Christian churches, for example, accept the scientificevidence for the age of the Earth, the beginnings andhistory of life, and recognise that the creation stories in“Genesis” are not literally true, but are allegories to thepower and benevolence of the Judaic-Christian-IslamicGod. The belief is that evolution happened, but underGod’s control and supervision, along a pathway Heordained.

Thus it is quite possible to reconcile religious belief andfaith with scientific enquiry and knowledge. Eachcontributes in its own way to human culture, and to eachindividual’s “humanity”.



ANCIENT TIMES MODERN TIMES

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

life-forms modern life-forms

Sediments are laid down on top of the previouslayer, so the lower layers are older.

Rocks and fossils llooccaattiioonn 11

Rocks and fossils llooccaattiioonn 22

foss

ils co

rrelat

e

from

one

plac

e

to an

othe

r

youngestfossil

Oldestfossil




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Worksheet 2

Fill in the blanks. Check answers at the back.

The age of the Earth is thought to be about(a).............. billion years. By about 4 billionyears ago (BYA) it is likely that many(b)........................................... compounds hadformed from the inorganic chemicals present.

The next step was probably that certain lipidmolecules (which are (c)........................................=water hating) may have come together andformed (d)............................................ Thesestructures, in which the lipid layer acts like a(e)........................................., may have trappedother chemical inside.

If the chemicals inside were able to(f)........................................ themselves, and toattract other molecules in through the“membrane”, then the structure is “alive”.This may have first happened about(g)...................... BYA.

For the next billion years, all life on Earth wasbacteria-like, (h)..............................................(living without oxygen) and heterotrophic,feeding on the (i).................................. moleculesdissolved in the oceans.

The first (j)............................................ (self-feeders) appeared about 2.5 BYA. They wereable to make food using the energy of(k)........................................... from theirenvironment. The first cells doingphotosynthesis were the (l).................................................., which grew in largestructures called (m).............................................They released (n)..............................................gas which reacted with dissolved(o)................................ This precipitated andformed extensive sediments, which are knownas (p)......................... .................................Eventually there was enough oxygen formedto turn the atmosphere from being(q).................................., to become oxic.

This was a disaster for many anaerobic cells,which became extinct. They were replaced bynew types which used (r)............................................................................. (process) to releaseenergy from their food in the form of theenergy chemical (s)......................

About 1.5 BYA, the first(t)................................................... cells (withmembrane-based organelles) appeared. Thebest explanation for these is called the“(u).............................................................Hypothesis” in which one cell ingestedanother, but failed to (v).......................................it. The smaller cell survived to live within thelarger, eventually becoming an organelle suchas a mitochondrion or (w)...................................Evidence supporting this hypothesis is thatsome organelles contain their own(x).............................. and .....................................for making proteins.

Roughly 1 BYA some cells began swappingbits of DNA in a primitive sort of(y)........................................................ Thisincreased the (z)............................................variation and 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” inthe fossil record, when many animals with(ae).......................... body parts appeared.





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Technology to Study ProcaryotesEven with a good light microscope, bacterial cells are sosmall that they appear as simple rods, spheres and spiral-shaped cells.

The Electron Microscopewith its superior magnification and resolution was thetechnology that revealed the fine details of cell structure. Itwas the electron microscope that first gave us theunderstanding of eucaryotic and procaryotic cells as beingfundamentally different.

This understanding led to the classification of all theprocaryotic organisms into the “kingdom Monera”, totallydifferent life forms to the eucaryotic plants, animals and fungi.

Within this procaryotic kingdom of life, many differentsub-groups were recognized, but they were all thought tobe essentially alike because of their procaryotic structure.New technologies have changed that view...

DNA & Protein Sequencingallow scientists to determine the precise sequence ofchemical units in DNA molecules and protein chains.

Studies on the different types of procaryotic organismshave shown that there are some types that are so differentfrom the rest, that they perhaps should be placed into anew kingdom, to be called “Archaebacteria” or simply“Archaea” (pronounced ark-ee-a).

What’s different about them? They have:• completely different RNA molecules to all other life• cell walls which are chemically different to all others• totally different enzymes for releasing energy from food • different pathways of metabolism for some cell processes

The word “archae” means “ancient”, and it is believed thatthese very different organisms are modern survivors fromthose primitive cells of 3 billion years ago.

The ArchaeaWhen the cyanobacteria began photosynthesizing in theirstromatolites just over 2 billion years ago, the oxygen theyreleased firstly caused the oceans to rust, and then causedthe 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...

The Methanogensare one type of the Archaea group. They cannot tolerateoxygen at all and live in habitats where there is none:• in the muddy sediments under swamps, lakes and the

seas and oceans.• in the digestive systems of many animals, especially the

ruminants, a group of grazing animals including cattle.

Their original habitat of 3 billion years ago was the anoxicoceans with an atmosphere containing the gases theyneed... carbon dioxide and hydrogen.

As the oxygen levels rose many died out, but the oxygennever reached some places such as the mud and sedimentsunder water, where the processes of decompositionremove any oxygen immediately, and produce carbondioxide and hydrogen from the fermentation of dead plantmaterial and other organics which settle into the mud.

The methanogens get their energy from the chemicalreaction:

Carbon dioxide + hydrogen methane + water

CO2 + 4H2 CH4 + 2H2O

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

As well as living in the decomposing sediments underwater, some methanogens live in the gut of animals. Othermicrobes help digest plant foods by fermentation,producing CO2 & H2. The methanogens convert thesegases to methane... intestinal gas.

3. THE PROCARYOTIC ORGANISMS TODAY

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NNuucclleeaarr rreeggiioonn,, bbuuttnnoo ttrruuee nnuucclleeuuss

PROCARYOTIC EUCARYOTICCELL CELL

RRiibboossoommeess iinn ccyyttooppllaassmm,,bbuutt nnoo mmeemmbbrraannee-bboouunndd

oorrggaanneelllleess

PHOTOMICROGRAPH ofMETHANOGEN cells



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The Thermoacidophilesare another group of the Archaea which are probablydescended from ancient types.(“Thermo-” = heat, “-acido-” = acid, “-phile” = loving.

They love hot, acid conditions)

The thermoacidophiles live today in extreme habitatswhich may be quite similar to the habitats they lived inbillions of years ago. Some are found in the boiling, acidicwaters of volcanic hot springs, like these in YellowstoneNational Park, in Wyoming USA.

Others have been discovered in the deep ocean, aroundvolcanic vents where they are the basis of some weird foodchains that do NOT depend on photosynthesis.

Thermoacidophiles are autotrophs capable of making theirown food from simple inorganic chemicals like CO2 &H2O. The energy needed for this comes not from sunlight,as in photosynthesis, but from the energy in certainnaturally occurring inorganic chemicals... they are“chemosynthetic”

The thermoacidophiles depend on hydrogen sulfide (H2S)which is abundant in the volcanic springs they live in andaround. It is H2S which gives the characteristic “rotten-eggsmell” of volcanic springs. It is poisonous to most life-forms (not to mention the boiling temperatures and highlyacidic conditions) but to these Archaea cells it is home-sweet-home, possibly just like the habitats they inhabited 3billion years ago on the young, volcanically-active Earth.

Some of the deep-sea chemosynthetic types have formedmutualistic relationships with giant tube worms, and are thebasis of food production in the totally dark ecosystemsthousands of metres deep. The chemosynthetic Archaeacells live inside the tube-worm’s body. The worm channelsH2S from the volcanic vents to the procaryotes which makefood for themselves and for the worms. An entirecommunity of crabs, starfish and mussels live on this foodsupply.

Other Possible Environments in Which Life Began

It is generally assumed that the first living cells formed inthe oceans of the primitive Earth. However, the Archaea(including many types other than the methanogens andthermoacidophiles) inhabit a huge range of extremeenvironments on Earth today.

Could this mean that it was in one of these extremeenvironments that life first began? Some scientists havesuggested that this could be the case:

The Volcanic Vent Scenariois one suggestion. We believe that the primitive Earth of3-4 billion years ago was a lot hotter than today, and thatvolcanic activity was very widespread.

The presence of the thermoacidophiles in modern hotsprings proves that life can thrive in such conditions, somaybe that’s where life actually began.

The Clay Sediments Scenariois another possibility. Some scientists have pointed to theimpressive catalytic properties of clay minerals called zeolites,which can attract organic molecules and cause chemicalreactions to occur, including polymerization, an essentialreaction to make the large, complex molecules of life.

They suggest that perhaps the first living cells began inzeolite clay sediments, where the necessary reactions of lifecould get some help from the clay itself. This might havehappened deep in the Earth, and it is interesting to notethat some Archaea types are found thriving (although insmall numbers) deep in the rocks of the crust.

The Ice-Concentration Scenariois a third possibility. Some scientists have doubts that theorganic chemical “soup” of the oceans could ever havebeen concentrated enough in “Urey-Miller chemicals” forenough chemicals to form microspheres and eventuallyliving cells. Experiments show that as sea-water freezes, thedissolved chemicals can be pushed together into smallzones of very high concentration.

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



Photos by Diana




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Worksheet 3

Fill in the blank spaces.Check your answers at the back.

Eucaryotic cells are those which have a truea).............................................................and otherb)...........................................-bound organelles.Cells lacking these features are calledc)................................................................... Thetechnology which allowed us to discover this wasthe d)...................................... ...................................

Other new technologies such ase)...................................................................................have shown that not all procaryotes are the same.One type, now called the f).....................................have significant differences such asg).................................................. We think theymay be descended from some extremely ancientcells from about h)................... billion years ago.

One type are called i)......................................because they produce methane from the gasesj)................................... and k)................................They live in habitats such as in thel)....................................... under water and in them)...................................... of many animals. Theseorganisms are n).................................................which means they live without oxygen, and infact would be o)............................................... by it.

Another type are thep)....................................................... which thrive inhabitats such as q)......................................................and in the deep ocean, aroundr)...................................................................................These organisms are s).....................-synthetic.They make food from simple inorganicchemicals, using energy fromt)....................................... (chemical name) which iscommon around volcanic vents. The deep-seavariety are vital to their isolated ecosystemsbecause they u)...............................................................................................................

Because the Archaea are so ancient, and becausethey live in such extreme v)...................................,it has been suggested that perhaps life did notbegin in the w)........................................as generallyassumed. Alternative places for life to havestarted include x).......................................... vents,in sediments of clays called y)...................................or even in cold places where chemicals couldbecome z)........................................................as thewater froze.


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The Need to Classify Imagine a supermarket without any system for placingproducts on the shelves. Baked-beans are under the lightbulbs, just beside the fresh tomatoes and the fish-fingers(which have rotted because they’re not in the freezer) andthe washing detergent. Oh, you want the smaller can ofbaked-beans? They’re somewhere else entirely! This would be chaos!

The branch of Biology concerned with putting the living“supermarket” into order is called “Taxonomy”. Overseveral hundred years a system of classifying living thingshas developed in order to:

• bring order to the study of millions of living organisms• help communication, by agreeing on a unique name for

each species• help the study of living things by placing them in groups

with similar characteristics• show the relationships between organisms, or between

groups, so that the evolutionary pathways can be more easily established.

The Criteria Used to ClassifyHow would you put the chaotic supermarket in order?Would you put all items of the same colour, or sizetogether? This would put the 1kg detergent (red pack) onthe same shelf as the 1kg bags of red tomatoes.

Morphological ClassificationTraditionally, biological classification uses “morphology”...the structure of organisms’ bodies and cells to place eachspecies into groups with others with similar structures.Using structural characteristics has several advantages:

• Usually, structural features stay the same throughout anorganism’s life, unlike (say) colour which could changefrom time to time.

• Structural features are often obvious and easily observedso that classification (at least at a general level) is quick and easy once you know the things to look for.

• Structural features are often the result of evolution, sothis can automatically lead to the placing of related speciesinto the same groups. (**this doesn’t always work)

**Example: Based on structural features, the snakes,lizards & crocodiles are classified together as “Reptiles”,while the birds are a separate group.

However, fossils and DNA evidence suggest thatcrocodiles and birds are actually more closely related thancrocodiles are to snakes & lizards.

Cladistic ClassificationIn recent times, the use of structural criteria is beingimproved and extended using information from newtechnologies such as the electron microscope and DNAand biochemical studies.

DNA and protein sequencing is able to determine the“relatedness” of species in an evolutionary sense. A systembased more on the evolutionary pathways is called a“Cladistic Classification”.

The advantage of a cladistic system is that the groupingsare truly “family trees” that put organisms together ingroups with their true relatives.

More and more, as fossil discoveries and the newtechnologies reveal more details about evolutionaryrelationships, the traditional Morphological classification isbeing adjusted and altered to become more Cladistic.Examples of these changes will be discussed later.

4. THE VARIETY OF LIFE & HOW WE CLASSIFY IT ALL

MORPHOLOGICAL CLASSIFICATION

BIRDDIFFERENT

SAME GROUP

Based on bodystructure

CLADISTIC CLASSIFICATION

SAME GROUP

Based on Fossils and DNAstudies, which show

evolutionary relationships

LIZARDDIFFERENT




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The Classification HierarchyA “hierarchy” means an organization involving levels. Forexample, an army has a hierarchy of command where acorporal or sergeant commands a section of soldiers, alieutentant commands a platoon of sections, a captaincommands a company of platoons, and so on, upwards. Asyou go upwards through the levels, you are including moreand more soldiers in each higher grouping.

The Biological Hierarchy works the same way:

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

Note: the Genus name must be written with a capital letter,but the species name must be written in lower case. Thename is usually underlined.

Species which belong to the same genus are very closelyrelated and will usually share many characteristics. Forexample; Felis leo , Felis tigris and Felis pantheris all belongto the same genus. They are in fact the lion, tiger andleopard... all instantly recognizable as very similar bigpussy-cats.

Their differences in colour and coat-pattern are trivial...that’s why such criteria are never used in taxonomy.

The Concept of a SpeciesWhat defines a species?

At all the higher taxon levels, body and cell structures areused to separate the groups. However, once you get downto members of the same genus, they are so similar in bodystructure that reproduction is used to define the differentspecies.

Two organisms are considered as belonging to the samespecies if they normally interbreed and produce healthy,fertile offspring.

In captivity lions and tigers have successfully interbred(producing “ligers” and “tigons”). However, this does notoccur in nature, so lions and tigers are considered asseparate species.

This reproductive definition of species works pretty wellfor animals, but often becomes confused among the plantsand microbes.

Level or “Taxon” Example: Human Example: Eastern Grey Kangaroo

KINGDOM Animals Animals (Eucaryotic cells, no cell wall)

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

enclosed in a vertebral column)CLASS Mammals Mammals (“warm-blooded”, furry, milk glands)

Sub-Class: Metatheria (Marsupials... pouched mammals)ORDER Primates (mammals with grasping Diprotodonts (Herbivorous marsupials)

hands, binocular vision)Sub-Order: Anthropoids (includes humans, apes & monkeys)

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

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

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

MORE GENERAL GROUPS

MORE SPECIFIC GROUPS

At the top of the “taxon” hierarchy the groupsare broad and general and contain many

different types.

As you go down the hierarchy the groupsbecome smaller until at the bottom you havedefined one specific organism... the species

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

Example: a “sub-order” is below, a “super-order” is above “order”.

You need to remember that the classification system is an arbitrary, human-mmade, artificial schemetrying 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.




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Classification KeysOne of the important aids to using the classificationsystem is the dichotomous key. “Dichotomous” means todivide in two, so it means the key always splits into 2alternative pathways. At each “decision point” twoalternative criteria allow you to choose the correct path totake, to eventually classify an organism into a taxonomicgroup.

The criteria used need to be structural, in keeping with thewhole concept of biological classification.

Dichotomous keys can be in diagram form like a flowchart, or contain a series of paired statements.

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

Level 1a) Has 2 pairs of wings ....................................go to level 2b) Has 1 pair of wings.......................................... DipteraLevel 2a) Front and hind wings have similar texture

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

thickness and/or texture .............................go to level 5Level 3a) Body has distinct, narrow “waist” between

thorax and abdomen................................. Hymenopterab) No distinct “waist” ...................................go to level 4Level 4a) Wings covered in patterned scales........ Lepidopterab) Wings clear, with many veins....................... OdonataLevel 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

One pair of wings

DipteraTwo pairs of wings

Front and hind wingsquite different inthickness and/or

texture.

Wings covered inpatterned scales

Lepidoptera

No distinct “waist” Body has distinct,narrow “waist” betweenthorax and abdomen.

Hymenoptera

Front wings onlypartly hardened.

Large mouthparts forgrasping or piercing

prey.

Hemiptera

Front wings totally“hardened” formingprotective cover for

rear wings.No large mouth parts

Coleoptera

Wings clear, withmany veins

Odonata

Front and hind wingshave similar texture

and patterns. Maybe different sizes.

Flow-Chart Diagram KeyChoose the correct path at each branch

Check your answers in answer section at back

Wing partlythickened

Patternedscales

Use the keys below to classify these insects

into groups (Orders)

TWO DIFFERENT TYPESOF DICHOTOMOUS KEY



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Changes to the Classification SystemThe biological classification system was developed over200 years ago. Since that time an enormous amount of newknowledge has been discovered which has, from time totime, necessitated changes in the way we classify life.

The best example is at the highest “taxon”, the “Kingdom”level. When the system was invented, all known living thingsseemed to be either plant or animal, so a “Two Kingdom”scheme was used. The fungi appeared to be rather weird plants,and later when bacteria were discovered, it was decided thatthey were closer to plants than animals.

Two Kingdom Scheme

By the middle of the 20th century it was realized that thisscheme was really not satisfactory.

The electron microscope revealed much more structuraldetail at the cellular level. The use of the ultracentrifugeallowed cell parts to be separated for chemical analysis andthe use of radio-isotopes for tracing biochemical pathwaysshowed up fundamental differences between living things.

The new technologies made scientist realize:• the enormous difference between procaryotic and

eucaryotic cells• that the fungi are not just weird plants... they’re a totally

different type of organism• that single-celled organisms are fundamentally different

to multicellular life, regardless of other characteristics.

This led to adoption of theFive Kingdom Scheme

More Changes in the Future?The new technologies of DNA and protein sequencinghave already revealed the fundamental differences betweenthe Archaea and the other types of procaryotes.

Because of this, many scientists are already using a

Six Kingdom Scheme

ARCHAEA ANIMALS PROTISTS

FUNGIBACTERIA PLANTS

However, this method is not Cladistic enough for others...it doesn’t show clearly enough the evolutionaryrelationships between the major groups. To do so, somescientists are beginning to use another taxon, called“Domain” which is higher than “Kingdom”.

Perhaps in the future we will use a scheme something like:

Three Domain Scheme

Domainsof Life

Sub-DomainsorSuper-Kingdoms

Kingdoms



LIVING THINGS

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

algae

ANIMALSEucaryotic, multicellular,heterotrophic, no cell wall

PLANTSEucaryotic,

multicellular,autotrophic, with cell-wall

MONERAProcaryotic

cells

PROTISTSEucaryotic, single-celled.

Includes plant-like and animal-like types such as single-celled

algae & protozoa

FUNGIEucaryotic, multicellular,

heterotrophic, with cell-wall

LIVINGTHINGS

BACTERIA EUCARYOTESARCHAEA

ANIMALS

PROTISTSsingle-celled

METACYTESmulticellular

PLANTS FUNGI

Until the exact details are agreed upon, we willcontinue to use the 5 (or 6) Kingdom Scheme

LIVINGTHINGS



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The Problems of Classifying Extinct SpeciesOur biological classification scheme is used not just fortoday’s living things, but for all the extinct species we knowfrom fossils.

There are problems classifying an organism from its fossilsalone:

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

• the new DNA technologies and biochemical analysis which are so useful for finding “relatedness” among living organisms, cannot be used on most fossils because the organic chemicals have not been preserved in fossilization.

For a fossil such as the skeleton shown below, there is noproblem classifying it. An expert in anatomy can probablydecide on its groupings all the way down to Genus, andeven assign it a species name.

For other fossils though, especially if they are very smalland very ancient, exact classification is impossible withoutDNA samples and well-preserved cellular imprints.

Clear cellular imprints are very rare, and DNA samples donot survive fossilization at all, except in a few rare cases ofanimals being preserved by freezing for a few thousandyears, but not for millions of years despite the “JurassicPark” scenario.



This is a life-size sketch of “Hallucigenia”, a bizarreanimal whose fossils are known from the famous

Burgess Shale deposit in western Canada.It lived over 500 million years ago, and its 7-part body

plan defies classification because it doesn’t seem torelate to any creature alive today.




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Worksheet 4

Fill in the blanks.Check answers at the back.

The branch of Biology which deals withclassification is called a).........................................

Some reasons for classifying are;• to bring some b)..................................................• to help c)...........................................................by giving uniformity of names• to help the study of life by placing organismsin groups which have d).........................................................................................• to show how organisms aree)........................................... in an evolutionarysense.

The criteria used to classify organisms areusually f)............................................... features,because these do not usually g)...........................during an organism’s life. Also, structures areusually the result of h)...........................................Classification based on structural features iscalled a i)...........................................................classification, while a “Cladistic” scheme isbased on j)...............................................................relationships. Modern technologies, especiallyk)............................................and l)........................sequencing are useful in determining“relatedness” for Cladistic schemes.

The classification hierarchy has 7 main levels,or m).............................The most general level is “Kingdom”, thencome n)..................................., o)..........................,“Order”, p).........................., q).............................and finally r)................................... Extra taxonscan be added between the main levels usingprefixes (s)................ (below) and t).....................(above).

To name a species, you use the u)........................and v).............................. names. If 2 specieshave the same genus name they must be veryw)...............................................................The definition of a species is based onx)......................................., so if 2 organismsnaturally produce y)............................... &............................ offspring then they are thesame species.

Classification keys are alwaysz)................................................... which meansto split in two.

The classification system is arbitrary andsubject to changes. For example, originally a 2kingdom system was used because everythingwas thought to be either aa).................................or ab)........................................... In the 20thcentury, improved knowledge resulted in aswitch to a 5-kingdom scheme: as well asplants and animals there were the kingdoms ofac)................................., (which are procaryotic),ad)................................................ (single-celledeucaryotes) and ae)................................................

It is likely that this will change again in thefuture, since it is already recognized that thekingdom “Monera” should be split intoaf).................................................. andag).......................................................

Dichotomous Key ExerciseUse the information given on page 17 aboutthe “Five Kingdoms” of living things toconstruct a dichotomous key.





20

LLIIFFEEoonn

EEAARRTTHH

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

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




21

Practice QuestionsThese are not intended to be "HSC style" questions, but tochallenge your basic knowledge and understanding of thetopic, and remind you of what you NEED to know at theK.I.S.S. principle level.

When you have confidently mastered this level, it is stronglyrecommended you work on questions from past exam papers.

Part A Multiple Choice1. Which of the following was probably NOT a common gasin the atmosphere on Earth 4 billion years ago?A. Carbon dioxideB. OxygenC. MethaneD. Ammonia

2. Louise Pasteur’s famous “gooseneck flask” experiment of1862 proved that::A. life could begin spontaneously from contact with air.B. organic compounds could not have been produced naturally

on the primitive Earth.C. a nutrient broth will rot after contact with air.D. the theory of “spontaneous generation” was wrong.

3. In the Urey-Miller experiment:A. organic molecules were produced from inorganic.B. living cells were produced from non-living chemicals.C. microsphere membrane structures were made artificiallyD. complex inorganic molecules were produced.

4. The technology that has allowed us to accurately measurethe age of rocks, fossils and the Earth itself is:A. radio-isotope studies.B. electron microscope.C. the “principle of superposition” of fossilsD. DNA sequencing

5. A “precursor” to the formation of the first living cells wasprobably:A. formation of an oxic environment.B. formation of chemical systems capable of photosynthesisC. formation of “microsphere” membrane structures.D. polymerization of natural inorganic chemicals.

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

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

8. The “Endosymbiotic Hypothesis” is a proposal for theformation of the first:A. procaryotic cells.B. photosynthetic cells.C. eucaryotic cells.D. cells capable of aerobic respiration.

9. The “Endosymbiotic Hypothesis” is supported by whichof the following pieces of evidence?A. Mitochondria contain their own DNA & ribosomes.B. Cells regularly envelop and “eat” smaller cells.C. Fossils of cells in “conjugation” have been discovered.D. Mitochondria can live independantly outside of their“host” cell.

10. It is thought that the correct sequence of certain eventsin the history of life was:A. sexual reproduction, eucaryotic cells, multicellular.B. eucaryotic cells, multicellular, sexual reproduction.C. eucaryotic cells, sexual reproduction, multicellular.D. multicellular, sexual reproduction, eucaryotic cells.

11. If you were to study an extensive fossil deposit, and workyour way down through the layers, you might expect thefossils to show a trend:A. of increasing complexity.B. of greater resemblance to modern life.C. of decreasing diversity.D. of younger and younger ages.

12. A cell like the one shown:A. may have lived when the

Earth was anoxic.B. may have been the first type

to appear on Earth.C. evolved from procaryotic

ancestors.D. could be a member of the Archaea.

13. The realization that the “Archaea” are very different toother procaryotes has come mainly from:A. use of the electron microscope to study the cells.B. study of the extreme habitats in which they live.C. discovery of fossil cells from 3 billion years ago.D. study of their biochemical pathways and DNA.

14. You would be unlikely to discover “methanogen” cellsliving 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.

15. The group known as ‘thermoacidophiles” are bestdescribed as:A. chemosynthetic autotrophs.B. autotrophic decomposers.C. photosynthetic heterotrophs.D. chemosynthetic eucaryotes.




22

16. Of the following “taxons” which one is the most generalgrouping, or least specific?A. FamilyB. PhylumC ClassD. Genus

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

18. In the “5-kingdom” classification scheme, if an organismwas described as “eucaryotic, heterotrophic andmulticellular”, it could belong to either of TWO groups:A. plants or protists.B. fungi or monera.C. animals or moneraD. animals or fungi.

19. If we were to adopt a “SIX kingdom” scheme forclassification, the existing kindom that would have to be splitup is the:A. Protists.B. Fungi.C. Monera.D. Plants.

20. The problem with classifying some extinct organismsfrom 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, etc are preserved.D. their original body parts have been “petrified”.

Part B Longer Response QuestionsMark values given are suggestions only, and are to give you anidea of how detailed an answer is appropriate.

21. (6 marks) Describe the conditions on Earth 4 billionyears ago, covering:a) significant physical conditions, andb) chemical composition of the atmosphere.

22. (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.

23. ( 3 marks)a) Explain how radio-isotopes have contributed to ourunderstanding of the history of life on Earth.b) Identify another recently developed technology andoutline its contribution to our knowledge of the history oflife.

24. (2 marks) Identify two major stages or processes that arebelieved to have occurred before the appearance of the firstliving cells on Earth.

25. (5 marks) One of the most significant events in thehistory of the Earth was the change from an anoxic to anoxic environment.a) What does this mean?b) Identify the organisms, and the process that caused thechange.c) Explain the significance of this change for the evolution oflife.

26. ( 4 marks)a) What does the “Endosymbiotic Hypothesis” attempt toexplain?b) Outline the hypothesis.c) Give a piece of evidence supporting the hypothesis.

27. ( 4 marks) Distinguish between procaryotic and eucaryotic cells, namingexamples of each.

28. ( 5 marks)a) Identify the technology which has produced evidence thatthe living procaryotes include two fundamentally differenttypes of life.b) i) Identify a group of organisms belonging to the

“Archaea”.ii) Describe the habitat of the group named in (i).

iii) Outline similarities between the current habitat ofthese organisms, and the Earth environment of the past.

29. (3 marks) It is generally assumed that life began in theoceans of the early Earth. However, there have been othersuggestions.Describe one possible alternative environment in which lifemay have originated. Give a reason why this idea is proposedas a serious hypothesis.

30. (3 marks) Give 3 reasons to justify the existence of abiological classification system.

31. (6 marks) Compare and contrast a Morphological to aCladistic classification scheme and give an advantage of each.

32. (2 marks) The horse and the donkey both belong thegenus Equus. They can interbreed producing healthyoffspring known as a “mule”. Mules are sterile and cannotproduce offspring.Should the horse and donkey be considered as members ofthe same, or separate, species? Explain your answer.

33. (5 marks) Use the following list of characteristics toconstruct a dichotomous key for the major plant groups.Group True leaves? Veins? Seeds? Seed structure?Algae No No No -Mosses Yes(simple) No No -Ferns Yes Yes No -Conifers Yes Yes Yes conesAngiosperms Yes Yes Yes flowers/fruits

34. (5 marks) Discuss, with reference to the “2-kingdom” andthe “5-kingdom” schemes, the impact of changes intechnology on biological classification schemes.




23

Answer Section

Worksheet 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 2a) 4.6 BYA b) organicc) hydrophobic d) microspherese) membrane f) 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 reproduction z) geneticaa) speeded up ab) multicellularac) algae ad) spongesae) hard

Classification Keys Exercise page 15

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

Worksheet 3a) nucleus b) membranec) procaryotic d) electron microscopee) DNA sequencing / biochemical pathways / protein sequencingf) Archaea g) 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 4a) 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) species

w) closely related / similar x) reproductiony) healthy & fertile z) dichotomousaa) & ab) Plant or animal ac) Moneraad) Protists ae) Fungiaf) & ag) Bacteria & Archaea

Make a Dichotomous Key Exercise There are many correct ways to do this. Format may be “PairedStatements” or “Flowchart Diagram”. A Good key will use onlystructural characteristics and it will be unambiguous, and (mostimportantly) it WILL WORK when used.

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

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

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

3. a) Cells have chloroplasts (photosynthetic)....... Plantb) Cells lack chloroplasts .................................... go to level 4

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

Practice QuestionsPart A Multiple Choice1. B 5. C 9. A 13. D 17. A2. D 6. B 10. C 14. B 18. D3. A 7. D 11. C 15. A 19. C4. A 8. C 12. C 16. B 20. B

Part B Longer Response QuestionsIn some cases there may be more than one correct answer. The following “model” answers are correctbut not necessarily perfect.

21.a) There would have been a lot of volcanic activity, constantlyadding volcanic gases to the atmosphere. Violent storms wouldhave been near continuous, with a lot of lightning.. Without anozone layer, there would have been high levels of UV radiationfrom the Sun penetrating to the surface.b) The atmosphere would have contained no oxygen at all, butbeen made up of gases such as carbon dioxide, nitrogen,ammonia, methane, hydrogen and water vapour.

22.a) The experiment was designed to test the hypothesis that the

conditions of the primitive Earth could have naturally producedorganic molecules.b) Flasks were set up containing the simple inorganic chemicalsthought to be present on the primitive Earth. The flasks wereheated, irradiated with UV, and electric sparks simulated lightning..After several weeks, the flask contents were analysed chemically.c) the flasks were found to contain organic chemicals includingsugars and amino acids.d) Conclusion: the hypothesis is supported. Organic molecules canbe produced from simple inorganic chemicals under theconditions thought to have existed on Earth 4 BYA.



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23.a) Because radio-isotopes “decay”, their radiation levels decline ina predictable way. This allows rocks & fossils to be accurately“dated”. Thus we have an accurate time scale for the history ofthe Earth & its life.b) DNA sequencing. This can determine similarities & differencesin the DNA of different species and is a measure of how closelyrelated they are in an evolutionary sense.

24.1. Production of organic molecules, which are the building blocksof living cells.2. Formation of “microspheres” from fatty lipid molecules. Theseact like membranes... necessary to form the first cells.

25.a) The change from an environment without any free oxygen gas(anoxic), to one with free oxygen (oxic).b) The cyanobacteria, carrying out photosynthesis, released theoxygen.c) When the Earth became oxic, many of the previously dominantanaerobic organisms became extinct, and it opened upopportunities for the evolution of cells using aerobic cellularrespiration.

26.a) Explains the evolution of the eucaryotic cells from procaryoticancestors.b) A larger procaryotic cell “ate” a smaller one, but failed to digestit. The small cell survived inside the larger one, and evolved tobecome an “organelle” such as mitochondrion or chloroplast.c) Mitochondria and chloroplasts contain their own DNA and itis bacterial-type. This suggests these organelles were onceseparate procaryotic cells.

27.Eucaryotic cells have a “true nucleus” and other membrane-bound organelles. Examples include all plants & animals.Procaryotic cells lack organelles, except non-membrane structuressuch as ribosomes. They have a “nuclear region” but no truenucleus. Examples are the bacteria, cyanobacteria and theArchaea.

28.a) Evidence for this has come from study of biochemicalpathways, protein, DNA & RNA sequencing, and chemicalanalysis of cell parts such as cell walls. This has shown that the“mainstream” procaryotes (e.g. bacteria) are distinctly different tothe Archaea.b) i) Methanogens

ii) Anaerobic muddy sediments under swamps, wetlands, oceans.iii) Their current habitats may be similar to those they occupied

3 BYA... i.e. anaerobic, lots of organic molecules available.

29.Life may have originated in zeolite clay sediments. Zeolites have achemical ability to attract organic molecules and to catalyzechemical reactions such as polymerization, which is essential forlife to get started.

30. Classification:1. brings some order and organization to the chaos of millionsof different species.2. helps communication by giving every species a unique nameagreed by all.3. places organisms into groups of similar types, making it easierto understand evolutionary relationships.

31.Both classification schemes place organisms into similar groups,and try to show the relationships between them.Morphological systems used cell & body structures as theircriteria. This has the advantage of being relatively easy to studyand observe.Cladistic systems attempt to place organisms into groupsaccording to their evolutionary “relatedness”. This has theadvantage of producing true “family trees” that help usunderstand the history and evolution of life.

32. They must be considered as separate species.The definition of a species is that 2 organisms are the samespecies if they can interbreed and produce healthy, fertileoffspring. Since the mule is sterile, the conditions of thedefinition are NOT met, so horse & donkey are not the samespecies.

33. (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

34. When the classification scheme was first developed it seemedthat all life was either plant or animal, so a 2-kingdom systemwas used.Later technologies, especially the electron microscope whichrevealed details of cell structures, and improved biochemicalanalysis, led to the realization that :• there are 2 totally different cell types... procaryotes &

eucaryotes.• the Fungi are not plants, but a totally different life form.• unicellular organisms are fundamentally different tomulticellular, regardless of being plant-like or animal-like at thecell level.The result was a change to the 5-kingdom system, recognisingAnimals, Plants, Fungi, Protists & Monera as beingfundamentally different.



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