GCSE Science Review Volume 17Number 2November 2006

A f lyingsuccess

1 Fruit flies and Alzheimer’s diseaseDamian Crowther

4 Improve your gradeEvaluating science in the news

6 Your futureScience communication

8 Investigating RTAsDavid Sang

11 UpdateAnimal testing

12 Fantastic fossilsNigel Trewin and Nigel Collins

15 Fats, oils and soapsDavid Moore

18 HurricanesDavid Sang

20 A life in scienceDrosophila melanogaster

22 Buckytubes

Contents

The front cover shows acoloured scanning electronmicrograph of the fruit flyDrosophila melanogaster(D. Phillips/SPL).

Words, words, wordsIn each issue of CATALYST you will come across many different

scientific words and phrases, in addition to the list of GCSEkey words at the start of each article. Use your GCSE ScienceEssential Word Dictionary, which you should have received freewith this issue, to look up the meaning of any words you areunfamiliar with and to develop your understanding of thoseyou already know. The Dictionary has been written by theeditors of CATALYST and so is tailored especially for allcomponents of your GCSE course.

The Dictionary also offers examiner’s tips — ways of gettingmore marks when you do your exams. These will be especiallyuseful for those of you preparing for your GCSE mock exams.When you are revising make sure that you do so actively —make notes as you go along. This will give you the best chanceof success in the exams. If you want a bit of light relief fromrevision, why not try the puzzle? It will help to get your mindworking.

David Moore

Volume 17 Number 2 November 2006

Free book for every subscriber!A single subscription to CATALYST, Volume 17, 2006/2007 is available to individualsat £16.95 per annum. Bulk orders of three or more subscriptions are available at thegreatly reduced rate of £8.95 per subscription, provided all copies can be mailed tothe same addressee for internal distribution. CATALYST is published four timesthrough the school year, in September, November, February and April. Orders can beplaced at any time during the year, and the issues already published will be suppliedautomatically. Only orders for complete volumes can be accepted.Every subscriber will also receive a copy of Philip Allan Updates’ GCSE ScienceEssential Word Dictionary (worth £5.99) FREE with the November issue. This offerapplies only to UK subscribers.Overseas rates are available on request.

EnquiriesFor more information or to place an order, contact Turpin Distribution, Pegasus Drive, Stratton Business Park, Bedfordshire SG18 8TQ.tel: 01767 604974fax: 01767 601640e-mail: custserv@turpin-distribution.com

Published by Philip Allan Updates, Market Place, Deddington, Oxfordshire OX15 0SE.www.philipallan.co.uk

© PHILIP ALLAN UPDATES 2006ISSN 0958-3629

Publishing Editor: Catherine Tate.Design and artwork: Caleb Gould.Reproduction by De Montfort Repro, Leicester.Printed by Raithby, Lawrence and Company, Leicester. Printed on paper sourced from managed, sustainable forests.

Editorial teamNigel CollinsKing Charles I School, Kidderminster

David MooreSt Edward’s, Oxford

David SangAuthor and editor

Jane TaylorSutton Coldfield GrammarSchool for Girls

Advisory panelEric AlboneClifton Scientific Trust

Tessa CarrickFounder Editor, CATALYST

David ChaundyFounder Editor, CATALYST

Charlotte CuretonBiotechnology and BiologicalSciences Research Council

Peter FinegoldThe Wellcome Trust

Peter JonesScience Features, BBC

Sarah LeonardScience Museum

Ted ListerRoyal Society of ChemistryFounder Editor, CATALYST

Ken MannionSheffield Hallam University

Andrew MorrisonParticle Physics and AstronomyResearch Council

Jill NelsonBritish Association

Silvia NewtonCheshunt School and Association for ScienceEducation

John RhymerBishop’s Wood EnvironmentalEducation Centre

Nigel ThomasScience EnhancementProgramme

T he instructions for constructing a livingorganism are encoded in long moleculescalled deoxyribonucleic acid (DNA). DNA is

contained within the chromosomes in the nucleus ofevery cell in all organisms larger than bacteria.

DNA and genesThe DNA molecules look like tiny twisted ladders;each rung on the ladder is formed by a pair ofchemicals called bases (Figure 1). There are fourdifferent bases, symbolised by the letters A, C, T andG, that can pair up (A with T and C with G) to makethe rungs. The order in which the bases are stackedup in the DNA molecule determines what the DNAdoes.

The function of much of the DNA in an organism israther mysterious; some may have no function at allwhile some is involved in controlling the cell. Onlysmall fragments of the total DNA have a clear functionand these parts are called genes. The DNA in a genetells each cell how to make a particular protein.

What do proteins do?Proteins have a wide range of roles in cells, but wecan think of them either as tools or as building blocksfor the organism:l They can be thought of as tools when they performan action such as digesting food (digestive enzymes),releasing energy from sugar (enzymes in respiration),carrying oxygen in blood (haemoglobin) or acting ashormones (insulin). l They can be thought of as building blocks whenthey make up bones, tendons (collagen), nails andskin (keratin).

To remain healthy the genes in the body mustproduce the correct amount of the right proteins.Small differences in genes cause the characteristics in people that we recognise as running in families,such as eye colour, hair colour, baldness and height.In animals and plants these genetic differences causethe characteristics that we can alter by selectivebreeding, such as milk production in cows or stalklength in wheat.

1November 2006

DamianCrowther

GCSE key wordsGenes

Genetic diseasesDNA

Mutation

Fruit flies andAlzheimer’s disease

T

T

G C

G

G

GC

C

A

A

G

C

G C

C

T

A

A

T

AT

G

G

A

In this article we look at some basic aspects of GCSE genetics and then at how fruit f lies arebeing used in novel ways to study genetic diseases.

Figure 1 DNA is likea spiral ladder with apair of bases for eachrung

Left: Colouredscanning electronmicrograph (SEM) ofthe fruit fly Drosophilamelanogaster on a leafEy

eof

Sci

ence

/SPL

How do genes cause disease?Random changes to a gene (mutations) may drasti-cally disturb the activity of a gene. This can result in amarked imbalance in protein activity, which showsitself as a disease.

AlcaptonuriaThe first genetic disease to be described, called alcap-tonuria, was discovered by Archibald Garrod in 1908.Patients with this disease suffer with arthritis (painand damage to joints) and Garrod noticed that theirurine turned black when exposed to the air. Thearthritis and the coloured urine are now known to becaused by the build-up of a chemical called homogen-tisic acid. Normally this chemical is removed by anenzyme (a specialised protein), but in sufferers thegene is mutated so that the enzyme is no longer active.If an individual inherits two copies of the mutant genethen he or she cannot remove homogentisic acid fromthe blood and develops the disease. Alcaptonuria is arare disease.

Cystic fibrosisOne of the commonest genetic diseases in the UK iscystic fibrosis. This is caused by mutation in a geneinvolved in mucus production. Individuals with twocopies of the mutant gene produce mucus that is toothick and sticks in the lungs, resulting in repeated lunginfections. This thick mucus is also produced in thegut and from other internal surfaces of the body.

HaemochromatosisSome genetic diseases are caused by mutations in genes that make their proteins overactive.Haemochromatosis, the most common geneticdisease in the UK, is an example of this; in this casethe mutant protein causes the body to absorb toomuch iron from the diet. Normally iron is required aspart of haemoglobin, the protein that carries oxygenin red blood cells, but too much causes damage tomany organs including the liver, heart and kidneys.

Alzheimer’s diseaseAlzheimer’s disease is a common cause of memoryloss in elderly people. About 5% of cases are caused bymutations that result in faulty forms of the enzymesthat would normally remove a potentially toxicprotein from the brain. Mutant forms of theseenzymes allow the accumulation of toxic peptidefragments (called Aβ peptides). As these Aβ peptidefragments build up in the brain the nerve cells that arerequired for memory stop working and the patientbecomes ill.

How do fruit flies get Alzheimer’sdisease?Genetic diseases are the subject of much research asscientists try to work out better treatments for them.One line of research is to utilise fruit flies with thehuman gene involved in Alzheimer’s disease

The fruit fly (Drosophila melanogaster) has been usedin genetic experiments for 100 years (see ‘A life inscience’, pages 20–21). Scientists are now able to makea lot of different transgenic flies by placing new DNAinto their chromosomes (see Box 2 and Figure 3). Ifthe DNA is a human gene then the flies can be made

2 Catalyst

Box 1 Useful websitesYou can listen to Damian Crowther talking aboutfruit flies and Alzheimer’s disease and see foryourself the effect of the Alzheimer’s gene on theflies’ behaviour at:http://flymodel.cimr.cam.ac.uk/questions.htmlA series of short videos answer such questions as:l What does a fruit fly have for breakfast?l How long does a fruit fly live?l How do we make a fruit fly get Alzheimer’s disease?l How do we know that a fruit fly has Alzheimer’sdisease?l How can we use fruit flies to test medicines?l How big is a fruit fly’s brain?l How do Alzheimer’s fruit flies behave?l Why do we study flies in medical research?

You can find out more about how Alzheimer’sdisease affects people at www.alzheimers.org.ukby clicking on > Facts about dementia > What isdementia? > Alzheimer’s disease.

In humans, the cellsfrom males and femaleshave 22 pairs ofchromosomes; femaleshave an additional pairof X chromosomes,while males have one Xand one Y chromosome.

Right: Flies withAlzheimer’s disease(on the left) are lessable to climb the testtube than normalactive flies (on theright). Read Box 1 tofind out how you canwatch these fliesclimbing

The average length ofthe DNA molecule in ahuman chromosome isabout 5 cm and we have46 chromosomes ineach cell. There areapproximately10 000 000 000 000cells in the body and sothe length of DNA inyour body in metres is 0.05 ×× 46 ×× 1013,which is about23 000 000 000 km.

Dam

ian

Cro

wth

er

Aββ is read ‘Abeta’.

to produce the corresponding human protein. If thehuman protein is involved in human disease we mayfind that the fly will suffer a similar disease. We canthen use these flies to test new treatments that couldbe useful for human patients.

We want to find treatments for Alzheimer’s disease,so we gave the fruit flies the human gene for the toxicAβ peptides so that they produced the peptides intheir brains. Using a microscope we looked carefullyat the brains of the transgenic flies (Figure 2); we alsomeasured their life-span and their walking abilities.We found that the Aβ peptides cause damage in thefly that is similar to the disease in the human brain.

Testing drugs for Alzheimer’s diseaseBecause the fly develops the disease within a few days,rather than after 50–60 years as in human patients,

we can do experiments much more rapidly. Impor-tantly, we can test new drugs on the flies by puttingthe drugs in their food and testing whether the flieslive longer or walk better. Since the genes in flies andhumans are very similar we can start to think aboutnew drugs for human patients by using the geneticinformation that we get from the flies.

Damian Crowther qualified as a medical doctor and specialisedin neurology (concerned with nerves and muscles). He now workson Alzheimer’s disease in the Departments of Medicine andGenetics at the University of Cambridge.

3November 2006

White eye

Inject plasmids into embryosfrom white-eye flies

Now in fly chromosome

Fly develops with a red eyeas a marker for the transgene

Transposase enzymesplices recombinantplasmid into embryo’schromosome

Mixplasmids

EmbryoPlasmids

Step 1

Step 3

Step 2

e.g. Aβ peptide gene foran Alzheimer’s disease fly

Recombinantplasmid

Plasmid

Red eyegene

Humangene

Transposase gene

Transposase gene

Red eyegeneHuman

gene

Red eyegeneHuman

gene

Box 2 Creating a transgenic flyThe process outlined below is illustrated in Figure 3.Step 1The first step in creating a transgenic fly is to splice(clone) the DNA for the human gene into a plasmidthat contains a second gene which makes acoloured protein that makes the fly’s eyes red.Step 2This recombinant plasmid is mixed with anotherplasmid which has the gene for an enzyme calledtransposase.Step 3Transposase is able to insert the recombinantplasmid, containing our gene of interest, into thechromosome of an embryo that would normallydevelop with a white eye.

If the recombinant plasmid is incorporated into thefly’s chromosome successfully then the offspringwill have red rather than white eyes. The red eye issaid to be a marker for the transgene.

Figure 3 Creating a transgenic fly

Figure 2 The toxic Aβ peptide accumulates in thebrains of patients with Alzheimer’s disease as plaques(panel a, brown). These deposits damage nerves thatare required for memory. In the transgenic fruit flies thesame peptide accumulates as plaques (panel b, black)and damages the brain function. The true size of theseimages is 1 mm across

l You will probablylearn in your sciencecourse about howtransgenic bacteria aremade. Check that youunderstand this andcompare it with Figure 3.Two enzymes are neededto insert the humangene and the red eyegene into the plasmid —what are they called?

Science hits the headlines when new discoveriesare made, or when it says something aboutissues such as climate change. The headline is

often sensational — ‘Mobile phones cause braincancer’ or ‘Global warming causes worse storms’, forexample. However, you should not accept such storiesuncritically.

News stories do not tell you all that you need toknow to have an informed opinion. They are shortand designed to catch your interest with a few facts,possibly an implication for the future and somepeople’s opinions. There may be errors, misconcep-tions or incorrect assumptions about the scienceinvolved.

You need to develop critical thinking skills, applyyour own knowledge and do some research to findout the whole story. Only then will you be able to joinin the discussion about the issues raised and how theyare likely to affect your life.

How reliable is the news story?Usually you do not have enough information toevaluate its reliability, but you may be told where theinformation comes from. Research from universities,research institutes or hospitals is normally reliable. If ascientific journal is quoted it means that otherscientists have reviewed the research and found itacceptable.

Do the people providing or reporting the science inthe news have anything to gain? People who stand tobenefit are described as having a vested interest. Youmight be getting a one-sided view as a result. Forexample, some years ago research that found harmfuleffects from consuming a particular artif icialsweetener was partly paid for by money from sugarproducers. Although the research seemed sound, thisfunding cast doubt on its value.

The BBC news and other science websites providelinks to research institutes where you can follow upstories in greater depth. These will help you to see ifthe news has been reported accurately.

For health stories, visit Hitting the headlines atwww.library.nhs.uk/rss/ where you will f ind an inde-pendent commentary on how accurately newspapershave reported research, the quality of the researchand links to other items.

4 Catalyst

Improveyour grade

The new GCSE science courses want you tothink about how science affects your life. Youmay be assessed on how well you can explainsocial issues and evaluate scientificinformation.

A useful andentertaining websitewhich keeps an eye on science in the newsand offers criticalcommentary iswww.guardian.co.uk/life/badscience/

Mobile phonescause brain

cancer

Link betweenMMR vaccineand autism

Evaluating science in the news

Global warming causesworse storms

Ingr

am

How have the findings been interpreted?News stories present one particular interpretation ofdata, but there may be others. Do other scientistsagree with the explanations given? Look at theresearch claiming to link the MMR vaccine andautistic spectrum disorders. Although very few expertsin this area agreed with the arguments against havingMMR, news stories didn’t often mention this fact.

Scientists may be in general agreement about aparticular explanation, such as the causes of climatechange, with just a few dissenting views, or there maybe a serious debate among rival theories like thoseabout the origin and future of the universe. Of course,when something really new and ground-breakingcomes along many people will disagree with it at first.

Scientists can never say that research data prove atheory, only that the data support it, or are consistentwith it, within the limits of current knowledge. Newfacts may come to light that change our ideas.

Whose views are being put forward?You should question the views that different peopleput forward, and judge whether the evidence they useto back up their arguments is enough to supportthem. Are they giving you well-established facts, theirown opinion, generally held views, or even a beliefbased on religion or philosophy? Do they have avested interest in the issues being discussed?

Jane Taylor teaches biology and is an editor of CATALYST.

The HFEA is the HumanFertilisation andEmbryology Authority.Its web address iswww.hfea.gov.uk/cps/rde/xchg/hfea

5November 2006

Box 1 Case studyLet’s look at a story that has beenrunning in my local paper which linksto aspects of your GCSE courseconcerned with hormones in infertilitytreatment and the use of stem cells.

The issueThe issue in question is:Should people be limited to oneembryo per IVF cycle?

l The facts — women aged 36–39 areas likely to conceive with a singleimplanted embryo as youngerwomen. The quality of the embryo ismore important for a successfulpregnancy than the mother’s age.l The research was done by a Finnishuniversity and reported in a scientificjournal. There were large numbers ofwomen in the study. It seems reliable.l Implications — people would behappier to have just one embryoimplanted, and fewer women wouldsuffer problems linked with multiplebirths.l The pressures — the HFEA wants women to have fewer embryos implanted per cycle of IVFtreatment because of the additional health risksand the economic implications linked with multiple births. However, IVF treatment is expensive (most people can only afford a couple of tries), stressful, uncomfortable and has healthrisks. Clients seek the highest likelihood of apregnancy first time so they want more embryosimplanted at one time.l Can science answer this question? Scientists cansay what is technically possible, and how risky theoutcomes are, but this is a decision that society as awhole must take.

l What’s the law? Assisted fertility is governed byregulations administered by the HFEA.

Possible researchTo take the issue further for a report you couldresearch:l What is IVF treatment?l What are the risks associated with multiple births?l How successful is IVF treatment?l Is the situation worse for older women?l What is the HFEA and what are its rules?

The HFEA website would be a good place to findout more, but don’t forget to list all your sources ofinformation.

New discovery gives olderwomen better chance with IVF

TopF

oto

T he most obvious science communicators arethose you meet on a routine basis in school —your science teachers. Maybe your school

organises visits to hear from science presenters, suchas Karen Bultitude (Box 1). Or you may have seenchemistry f ilms in school made by multimediaproducer Ted Lister (Box 2).

6 Catalyst

Your future Science

communicationAll scientists need to be good at communicatingabout their research with their fellow scientistsand with people who need to make direct use oftheir work. Many become engaged with a muchwider audience — both adults and young people.

Box 1 Karen Bultitude: presenter and facilitator

l Some science degreesinclude a sciencecommunicationmodule. There is onestand alone degree inscience communicationand policy. Find outmore at www.ucas.ac.uk> course search > 2007 >subject search > s >science > sciencecommunications.

l Log on towww.prospects.ac.ukand enter sciencecommunication in thesearch box. Also tryeducation officers, forcompanies andinstitutions.

If you have been to a science and technology showrecently there is a good chance you might have seenKaren in action. She devises, develops and managesa wide range of projects that take science to publicaudiences. She presents spectacular popular sciencelectures such as Cool Science and Our Planet — OurFuture. Or you might have seen her in the team ofyoung female scientists competing in Scrappy Races,an extension of Scrap Heap Challenge. She alsocontributed to Einstein Year and took physics toGlastonbury Festival.

How did Karen get involved with this? She explains:

At school I got the opportunity during the holidays toattend science schools, both in Australia (where I grew up)

and overseas. All sorts of activities were arranged for us,including lectures and tours by scientific experts in cuttingedge research such as chaos theory and cosmology. I alsomet other young people who were interested in science,which reassured me that I was normal and not a freakygeek! When I started doing research myself I felt I owed itto the next generation of students to provide them with thesame inspirational opportunities that I had received. And,of course, it’s a lot of fun.

In 1999 Karen won a Commonwealth Scholarship toOxford University where she was awarded a PhD inAtomic and Laser Physics in 2003. Now she works asa Research Fellow in the Graphic Science Unit at theUniversity of the West of England in Bristol.

Karen demonstrating ‘musical coat-hangers’ at Glastonbury Festival. This trick works by hanging coat-hangersfrom people’s index fingers with string then asking them to put their fingers in their ears. If you hit the hangerwith a metal object they will hear a loud deep chime

There are no formal qualif ications for the rolesKaren and Ted describe in Boxes 1 and 2, but, incommon with most people involved with sciencecommunication, they needed:l a good understanding of the sciences (to degreelevel)l the ability to express themselves clearly in bothwriting and speechl a reasonable level of computer literacyl the ability to get on with people and work bothalone and as a member of a team

Other career optionsOther possible occupations in science communicationare listed below, along with links to websites whereyou can f ind out more about the opportunitiesavailable.

Science centres and museumsThese often have interactive exhibits and activities.They are open across the UK and employ variouspeople, including explainers, guides and designers ofexhibits. You can explore a number of these at the

24 hour museum website (www.24hourmuseum.org.uk/trlout/TRA11863.html).

Science drama groupsThese develop and tour productions. Some, such asYTouring explore issues, others, such as Kinetic orQuantum Theatre groups, illuminate basic science.Their web addresses are in the margin.

Science writersScience writers generate articles for newspapers andmagazines, technical manuals and books. Log on towww.absw.org.uk and click on So you want to be a sciencewriter to find out more.

Science broadcastingAs well as correspondents and presenters, producersgenerate programmes, such as Tomorrow’s World,science documentaries and natural history pro-grammes. To find out about some presenters’ lives,log onto www.bbc.co.uk and then click on > Science &Nature > TV & Radio Follow-up > Presenters.

Nigel Collins teaches biology and is an editor of CATALYST.

7November 2006

Box 2 Ted Lister: writer/video producerTed was a teacher for several years before hebegan to write articles and textbooks and wasinvited to become a founding editor of CATALYST.He sent one of his CATALYST articles to theEducation Guardian and started writing for it.After a year’s secondment to the Royal Society ofChemistry (RSC) to write a book of experimentsfor teachers, he was asked to produce a video andhas continued to work for the RSC ever since. Teddescribes what he does in more detail:

There is no simple job title for what I do, which ismostly producing material to help teachers to teach,and school students to learn, science — chemistry inparticular. This is in a variety of media — print, videoand interactive packages for computer. Increasingly itis the last two. I work closely with others — I cannotlay out a book, use a camera or program a computerbut I work alongside people who can.

The job is very varied — one day at the computer,another out at a chemical plant with a film crew,another talking to scientists working at the cuttingedge. (I once talked to three Nobel prize winners in asingle day!)

There is no set route into this field — most of thepeople I know work on a freelance (self-employed)basis and work for several different organisations.I have done work for book publishers, the RSC, Corus(formerly British Steel), GlaxoSmithKline and manymore. Working freelance does lack security but can beliberating in that you can work when and how youlike.

Ted Lister receiving an award for a book he wrote for the Royal Society ofChemistry. His book, Cutting Edge Chemistry, won the 2001 British Book Designand Production award in the Educational/College Category

l Log on towww.ytouring.org.uk andwww.quantumtheatre.co.uk to find out moreabout these dramagroups.

R oad deaths in the UK are decreasing steadily(see Box 1). There are several reasons for this —better driving, safer cars, fewer pedestrians on

the roads and better traffic management. However,any accident can have a tragic impact on the familiesof those involved, so it is important to find out justwhat occurred.

Skidding to a haltAccident investigators often want to find out how fastvehicles were moving at the time of an accident.Individual witnesses cannot be relied on, so the crashsite is examined carefully and any skid marks on the

road are measured. Skidding occurs when a driverslams on the brakes in an effort to stop quickly, butthe friction with the road (which is the force that

8 Catalyst

Investigating RTAs

David Sang

GCSE key wordsAccelerationEquations of

motionMomentum

Crumple zone

An RTA is a road traffic accident. After any accident, the police and other investigators try toestablish what went wrong. This may be with a view to prosecuting a motorist, or simply in aneffort to improve road safety. An understanding of the physics of motion plays a large part insuch investigations.

Box 1 Declining death ratesRoughly 100 children aged 11–15 die on the UK’sroads each year. The number of people killed orseriously injured is decreasing steadily (see Figure 1),and is ahead of the government’s target of a 40%reduction in casualties by 2010, compared to the1994–98 average.

Figure 1 People killed or seriously injured on the roads, 1991–2004

60 0009000

8000

7000

6000

5000

4000

3000

2000

1000

0

50 000

40 000

30 000

20 000

10 000

01991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2010

target

All

ages

All ages

Children (under 16)

Year

Chi

ldre

n (u

nder

16)

Right: A policeaccident investigatormakes photographicrecords at the sceneof an accident nearKing’s Cross station,London M

icha

el D

onne

/SPL

stops the car) is insufficient. The wheels stop spinningas the brakes are applied, but the car continuesmoving, leaving a trail of black rubber behind eachtyre. A low-friction surface results in longer skidmarks.

How can the skid marks be interpreted? One way isto drive a car at a known speed on the road surface inquestion and to cause it to skid deliberately. From thelength of its skid marks, the deceleration of the carcan be deduced. Box 2 shows the equation of motionused.

Any car travelling on the same stretch of road isassumed to decelerate at this rate when it skids. So,given the length of a skid mark, the car’s initial speedcan be calculated. A driver who can be shown to havebeen exceeding the speed limit could be in big trouble.

FrictionDeceleration is often expressed in terms of the accel-eration due to gravity (g), which has a value of about10 m/s2:

a = −µg (where µ is the coefficient of friction ofthe road surface)

In the example above, the coefficient of friction (µ) is0.8, a good value for a road surface. On a smoothroad surface, µ might be 0.6 or less.

If the stretch of road concerned is short, or too busyto interrupt the traffic with test skids, an alternativemethod is used. A small ‘sled’ fitted with sections oftyre is dragged along the road (Figure 2). The pullingforce (F) is compared with the weight (µg) of the sled,and the coefficient of friction is calculated using:

µ = F/mg

Momentum calculationsAnother method of deducing a car’s speed before acollision uses the idea of momentum. An object’smomentum is found by multiplying its mass (m) andvelocity (v):

momentum = mv

Suppose a fast-moving van collides with a stationarycar (Figure 3). The two move off together. From thedistance they move, the total velocity of the van andcar can be found. But what about the original velocityof the van? After the collision, the combinedmomentum of the two vehicles is equal to the originalmomentum of the van.

We can calculate that in this example the van’svelocity was 24 m/s (about 86 km/h). Investigatorswould be interested in comparing this with the speedlimit, or the safe driving speed for the situation inquestion.

Passenger safetyIdeas about momentum are also important whenconsidering the safety of people in a vehicle when it isinvolved in a collision. Most modern cars have airbags, and seat belts are fitted as standard.

9November 2006

ExampleA car travelling at 20 m/s (72 km/h) skids to a haltin a distance of 25 m. What is its deceleration(negative acceleration)?

v2 = u2 + 2as

0 = 400 + 2a × 25

a = −400/50 = −8 m/s2

ExampleA van (mass 2000 kg) collides with a stationary car(mass 1200 kg). They move off at 15 m/s. How fastwas the van travelling at impact?

Total momentum after collision = 3200 kg × 15 m/s= 48 000 kg m/s

This must have been the value of mv for the vanbefore the collision, so:2000 kg × v = 48 000 kg m/s

Box 2 Equations of motionThere are three equations which relate the initialand final velocities (u and v) of an object to itsacceleration (a), displacement (s) and time (t).These equations only apply to an object whoseacceleration is constant.

v = u + at

s = ut + 1–2 at2

v2 = u2 + 2as

The third of these is the most relevant to accidentinvestigations because after the event it is difficultto discover the time (t) in which a vehicle’s velocitychanged during an accident.

Figure 2 ‘Sled’ used for friction/skid testing Figure 3 Van colliding with stationary car

30 30

1200 kg car2000 kg van

AfterBefore

Velocity v Velocity 15 m/s

Momentum is aquantity that isconserved — there isalways the same totalamount before andafter a collision or otherevent, but it is sharedout differently betweenthe interacting objects.

It is useful to rememberthat 10 m/s is equal to36 km/h or about22.5 mph.

A passenger in a moving car has momentum. When the car stops in a collision, the passenger’smomentum is reduced to zero. A force acts on thepassenger: this can be a big force acting for a shorttime, or a small force acting for a longer time.

force × time = change in momentum

A large force could seriously harm the passenger, soseat belts are designed to allow the passenger to moveforwards slightly during the impact. This means thatthe impact takes longer and the average force is less.Similarly, an air bag provides the force needed toprevent the passenger from flying forwards into thewindscreen. The bag inflates almost instantaneouslyon impact, and then deflates gently as the passengerpresses into it.

Cars themselves are designed to reduce the impacton the occupants. At the front and back are twocrumple zones; these collapse during a collision,absorbing much of the energy of the moving car. Atthe same time, the passengers are contained in a rigidcentral compartment. This rides up over the engine,which is a massive solid object that could do greatharm to the passengers.

David Sang writes textbooks and is an editor of CATALYST.

10 Catalyst

Box 3 Understanding teenagersTRL (the Transport Research Laboratory) is anorganisation which tests cars, investigates accidentsand monitors traffic flow. In its efforts to reduceroad accidents, it also looks at the psychology of drivers and pedestrians. A recent survey ofteenagers found that more than half of all accidentsto pedestrians aged 11–16 occur when they are outwith friends.

Teenagers surveyed by TRL admitted that theywent in for ‘risk-taking behaviour’, such as crossingthe road in hazardous conditions, mainly toimpress their friends. TRL hopes that its findingswill allow it to develop road safety strategies toreduce the death rate on the roads further.

How did TRL find out about the behaviour of teenage road users? It used a number oftechniques: interviews, roadside videos, analysis of police accident files, surveys of students and areview of published studies. Each of these on itsown could not give a full picture, but together theyprovide a strong body of scientific evidence.

Right: The EuropeanNew Car AssessmentProgramme(www.euroncap.com)tests the latest carsfor safety. Here youcan see the dummydriver and child seat;these are fitted withsensors to measurethe effects of a head-on impact

Below: It is importantto protect pets, too,when travelling. A20 kg dog flyingaround the passengercompartment of a caris a serious hazard

l Check out the safetyequipment for dogs and other pets atwww.petsafetybelts.com

l Find out more aboutthe work of TRL atwww.trl.co.uk. Its‘Online Store’ includesmany downloadableimages and reports.

The quantity force ××time is known as theimpulse of the force.

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In the UK research using animals is regulated by theAnimals (Scientific Procedures) Act 1986, whichcovers the breeding and supply of animals, how

they are looked after and what they can be used for.Researchers who want to use animals must obtain alicence from the animal procedures division at the UKHome Office. They must explain the nature of theresearch, what they expect to find out and what theyare doing to minimise the number of animals usedand to safeguard their welfare.

Scientific proceduresEach year the government publishes a report on theuse of animals in research — Statistics of scientif icprocedures on living animals, Great Britain (2005). Thiscan be accessed on the internet and covers activitiessuch as breeding, as well as experiments.

Just over 2.9 million scientif ic procedures usinganimals started in 2005: 14% were for toxicity testing

(a figure that has fallen significantly); 39% were forbreeding; the others were mainly for immunologicalstudies, pharmaceutical research and development,anatomy and cancer research. Of these procedures,85% used rats and mice, 4% birds and 8% fish. Almostall the animals were sourced in the UK.

Genetically modified animalsOverall, the number of animals used has fallensubstantially over the last 25 years, but the number ofprocedures involving genetically modified animals isincreasing rapidly. In 2005, 957 500 procedures (33%of the total for the year) used genetically modified(GM) animals — a big rise since 1995. The use ofgenetically modified animals is likely to increase stillfurther over the next 10 years.

Most GM animals, about 95%, were ‘knockout’mice. Specific genes are ‘knocked out’ to help showhow the disabled gene functions normally and howthis may be linked with disease. Two thirds of the GManimals were used to maintain breeding colonies;about one third were used for research.

The chief of the Home Office division makes thepoint that few GM animals have obvious healthproblems. Only 10% of procedures used rats, mice orother animals with harmful, but naturally-occurring,genetic mutations.

Dogs, cats, horses andprimates, which havespecial rights, were usedin less than 1% ofactivities in 2005; 3,120macaques and otherprimates were used,mainly to conform topharmaceutical safetyand efficacy testingregulations.

Update

Research using animals causes heated debate.New drugs must be safety tested on twospecies of animals, but how many experimentsuse animals and how are they regulated?What about genetically modified animals?

11November 2006

A transgenic mouse with musculardystrophy. Muscular dystrophy is aninherited muscle disorder. Nocurative treatment is known. It ishoped that this research will enablescientists to understand more aboutthe genetic basis of the disease and develop a gene therapy

Animal testing

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l Government statisticscan be found on theHome Office website(www.homeoffice.gov.uk/science-research).

P arts of Scotland were much warmer 410 millionyears ago. At that time, land that is now part of Aberdeenshire was south of the equator.

There were mountains and valleys, scattered vol-canoes and local hot springs and geysers (Figure 1).Vegetation was sparse, less than a metre in height andconcentrated in wet and damp areas, forming a miniforest in this early Devonian landscape. There weremany exotic life forms here and in freshwater pools.

This was the time in geological history when terrestrialplants and animals were evolving rapidly and creatingcomplex, new terrestrial and freshwater ecosystems.

The Rhynie chertFrom time to time, hot silica-rich water erupted fromthe hot springs and geysers, flooded the land surface,invaded the freshwater pools and deposited silica in aform called ‘amorphous opaline sinter’. The sintertrapped and preserved a huge variety of early land-inhabiting organisms. The sinter is now preserved as afinegrained quartz rock known as the Rhynie chert.

This rock was discovered in 1912 as loose blocks inthe fields around Rhynie near Aberdeen in Scotland.Further material was uncovered by trench digging anddrilling. It has been the subject of periods of intenseresearch involving institutions from around the worldever since and is now recognised as the best-preservedearly terrestrial ecosystem anywhere in the world.

Because the organisms were preserved very rapidlyin situ before they were buried, many of the fossils ofplants and animals have survived in perfect threedimensions, just as they were 410 million years ago(see Boxes 1 and 2).

Plant species in the chertThe silica coated plant surfaces and then quicklypermeated the plant tissues, preserving cellularstructures in minute detail. The flora found in thechert include seven named higher land plants, all lessthan 40 cm tall (Figure 2). It is possible to see thepores (stomata) for gas exchange on some plantstems, as well as structures called rhizoids, which arelong single cells, like the roots hairs on the roots ofhigher plants (Figure 3).

Fantastic fossilsNigel Trewinand

Nigel Collins

GCSE key wordsFossil

ExtinctionEcosystem

You have probably encountered fossils of the bones or shells of individual animalsembedded in sedimentary rocks. This articlelooks at some extraordinary fossils of plantsand animals preserved together in anecosystem — it is even possible to see the cells of which they were made.

12 Catalyst

Volcanoes

Geysers and hot springs

Buriedsinter

Sinter locally colonised by plantsand invertebrates

Figure 1 Landscape plus stratigraphy beneath the Rhynie chert

Active geysers andhydrothermal springsstill exist in some areastoday (e.g. YellowstoneNational Park in theUSA). Scientists canstudy what is happeningto organisms in theseenvironments andcompare this withsimilar features seen in the Rhynie chert to help them interpretthe ancientpalaeoenvironments.

Above: Sectionthrough Rhynie chertshowing the stems ofa fossil plant

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Plants are present at different stages of their lifecycles, so these can be worked out. It is even possibleto look at microscopic spores that were caught up inthis process of fossilisation as they were just germi-nating. Algae, fungi, a lichen and various bacteria are

also fossilised in the chert. The plants are preservedwhere they grew, some with stems still in the uprightgrowing position.

Animal species in the chertScientists have described at least 15 different namedspecies of early terrestrial and freshwater arthropods— animals with exoskeletons, segmented bodies andjointed limbs — that have been found in the chert.

13November 2006

Box 1 How do fossils form?

Box 2 Looking at the fossils in theRhynie chertThe rock containing the fossils is cut with adiamond saw, then slices are mounted on glassslides and carefully ground down to the correctthickness. The slides can then be viewed under amicroscope to reveal the anatomical details of theplants and animals. Many sections are needed tomake a full reconstruction. The research requiresskill and patience, and it takes many months todescribe fully the details of a new arrival forpublication in a scientific journal.

Fossils include teeth and bones, petrified remains(turned into stone) and impressions of various partsor marks left as animals moved around. Most can beplaced in one of the following groups:l hard parts of organisms that remain unchanged —teeth, bones and shells of ancient organisms maysurvive little changedl soft parts of organisms that are unchanged —some animals, now extinct, died in cold places andfroze; insects and other small creatures may betrapped in tree resin which over time forms amberl changed hard parts — parts of the structure ofbones, teeth or plant material may be replaced withminerals to form rockl changed soft parts — even though the soft parts ofan animal may have disappeared, they may leave animprint that reveals something of their structure

Apart from unaltered remains, fossils can form inthe following way:l The organism falls to the sea floor, into a pool oronto mud.l It becomes covered in sediment.l The sand or mud is compressed as more sedimentis deposited on top.l The organism may disappear completely and thespace may be filled with minerals, or a space may beleft, leaving a mould.l Sometimes the organic material remaining isslowly replaced with minerals — for example, fossilwood shows the cells and vessels just as in existingtrees, but the walls are formed of silica instead ofcellulose. Other minerals that may replace theoriginal material include calcium carbonate, ironpyrites and oxides of iron.

Older rocks containolder fossils. It issometimes possible tostudy a sequence offossils in progressivelyyounger rocks, revealinghow organisms evolvedover time.

Silica is silicon oxide(SiO2), a glassysubstance.

Figure 2 An artist’s impression of Devonian plantsgrowing at a pool margin near what is now Aberdeen

Figure 3 Rhynia, a plant from the Rhynie chert: (i) reconstruction; (ii) cross-sections of stems, preserved as they were growing; (iii) a stemsection in detail x = xylem, p = phloem, oc = outer cortex, ic = inner cortex, e = epidermis, c = cuticle (scale bar = 2 mm); (iv) transverse cross-sectionthrough a stoma showing the two guard cells (g) with the stomatal chamber (c) beneath (scale bar = 20 µm)

(i) (ii)

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l Can you identifyRhynia in Figure 2?

More species are currently being described or awaitingpublication in science journals. These animals includedetritivores living in plant litter, and carnivores thatpreyed on other arthropods (Figure 4). The wholeecosystem can be studied in detail.

Because of the unusual way in which fossilisationtook place it is also possible to look in great detail at the structure of some very small animals. Oneexample, a shrimp-like crustacean, Lepidocarisrhyniensis, lived in the small short-lived pools amongthe hot springs, feeding on detritus, much like fairyshrimps do today (Figure 6).

Another example is that of the trigonotarbids,which were spider-like creatures. Try to match thephotograph to the reconstruction (Figure 5). Thedetail revealed is incredibly fine, showing the delicatebook lungs used by the animal for gas exchange in air.

The oldest hexapods (six-legged animals) have alsobeen found in the Rhynie chert and include a springtailand representatives of two primitive insect groups.

ConclusionThe diversity of life recorded in the Rhynie chert is fargreater than that at any other site in the world with aterrestrial biota of a similar age. Scientists have alsobeen surprised by the complex symbiotic and parasiticrelationships of the interactions between plants,animals and fungi found in the early Devonian period.

Nigel Trewin is Professor of Geology and Petroleum Geology atthe University of Aberdeen, and has done a great deal ofresearch on the Rhynie chert. Nigel Collins teaches biology andis an editor of CATALYST; he first met Rhynia as part of hisbotany degree course.

14 Catalyst

The oldest knownHarvestman spider hasbeen found in the chert,as well as the oldestnematode worm.

Figure 5 (i) Reconstruction of a trigonotarbid arachnid from the Rhynie chert,Palaeocharinus rhyniensis, showing segmented abdomen (a), walking legs(l), pedipalps (p) and head (h) with lateral (la) and median eyes (m) (scale bar= 2 mm). Try to match the fossil section (ii) to the reconstruction

Figure 4 Castrocollis wilsonae was a detritivore/carnivore that inhabited short-lived freshwater ponds(similar to modern tadpole shrimps). In thisreconstruction it is shown with a hypotheticalcephalothoracic shield. The animal in the lower rightof the image is next to a primitive plant, a carophytecalled Palaeonitella cranii

The Devonian period ran from 410 to 365 million years before the present day.

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Light micrograph of a fairy shrimp, an aquaticcrustacean

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Box 3 Useful websitesl To explore the fossils of the Rhynie chert in moredetail, log on to: www.abdn.ac.uk/rhyniel For an overview of a number of differentorganisms in the fossil record, log on towww.bgs.ac.uk and click on Fossils.l You can find out more about fossils in the UK bylogging on to: www.discoveringfossils.co.ukl To find out about careers in paleontology, log onto the Natural History Museum website atwww.nhm.ac.uk and click on > Research andcuration > Science departments > Palaeontology.

Figure 6Reconstructionof Lepidocaris.This shrimp-likecrustacean livedin small poolsand fed ondetritus, muchlike fairy shrimpsdo today (seephoto above)

F ats and oils extracted from farm animals havebeen used as lubricants, in cooking, as fuel foroil lamps and in candles for centuries. Another

source of animal fat is the whale. Before the IndustrialRevolution whale hunting was done on a small scale,but after the development of harpoon guns in the1870s it increased signif icantly. Every part of thewhale was used — the chins, tongues and meat asfood, and the blubber for making oil, margarine andsoap. Whale blubber was boiled with sodiumhydroxide to produce soap. This process of boilingwith sodium hydroxide is called saponification.

Many nations, including the UK, fished for whalesfor oil and food, which resulted in several species ofwhales being driven almost to extinction. Othersources of oil were sought and whaling has nowlargely stopped. Today, useful oils are extracted fromthe fruits or seeds of plants — the most popular beingsunflower oil, olive oil, soya oil and palm oil.

SoapVegetable and animal oils contain esters. These aregroups of carbon and oxygen atoms (Figure 1) whichcan be split using sodium hydroxide to form long-chain hydrocarbons with an organic (carboxylic) acidgroup at one end (Figure 2). The long chain ishydrophobic (‘hates water’) and so will dissolve ingrease or dirt; the acidic end is hydrophilic (‘loveswater’) and so will attract water molecules. The otherproduct is glycerol (propane-1,2,3-triol). Figure 3 (on page 16) shows how soaps work.

David Moore

GCSE key wordsOil extractionSoap action

Vegetable oils

This article investigates a few of the uses ofnaturally occurring oils. These oils areextracted from animal fats or plant seeds andcan be turned into a variety of compoundsincluding soaps, fuel and margarine.

15November 2006

Fats, oils and soaps

Figure 2 Using sodium hydroxide to split esters

C O R2R1

R = alkyl groups (chains of carbon and hydrogen atoms)

O

The R groups arelong-chain carboncompounds.

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C O C + 3NaOH →R2 + 3NaOH

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Commercial whalingwas banned worldwidein 1986. Whaling todayis done for scientificpurposes, althoughsome countries are keento resume commercialwhaling.

Left: The crew of aJapanese whalingvessel measures thecarcass of a whaleduring a researchmission in theAntarctic in 1993.There is muchopposition to this so-called ‘scientificwhaling’ carried outby the JapaneseM

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Figure 1 Ester

Soap and waterOne problem with soap is that it reacts with dissolvedcalcium and magnesium compounds in hard waterto make scum rather than a lather. The soap reactswith the calcium and magnesium ions to producecalcium stearate (scum). Hard water containingdissolved calcium is good for bones and teeth.

Soft water does not contain these ions and soproduces a lather with soap. Soft water is better foruse in industry as it does not precipitate out limescaleon the inside of pipes. However, soft water containsan excess of sodium ions compared to hard water andthese have been linked to heart disease.

DetergentsDetergents were developed to prevent scum formingwith hard water. They contain a long hydrocarbonchain, like soap molecules, but at one end they have abenzene sulphonate group (C6H4SO3

− Na+). Thisgroup does not react with calcium or magnesium sodoes not produce scum in hard water.

If the detergent contains straight chain hydro-carbons it will biodegrade slowly. If the hydrocarbongroup is highly branched bacteria have diff iculty in breaking it down and it can accumulate in the environment. Detergents with a large amount ofbranching cannot be sold in the UK.

Problems with detergentsA typical packet of detergent contains about 20%detergent and between 0 and 30% inorganic phos-phates. The phosphates help to remove solublecalcium salts. Unfortunately, the phosphates end up inthe sewage system and then in rivers and lakes wherethey act as a nutrient for certain algae. The algaereproduce and cover the water. Underwater plantscannot photosynthesise due to the lack of lightreaching them. These plants die. Bacteria feeding onthe decaying plant material use up oxygen in the water.As a result, other aquatic animals die due to lack ofoxygen. This process is known as eutrophication.

Oils in paintsFor centuries painters have used oils that harden onexposure to air. Some oils — such as linseed oil —contain double carbon–carbon bonds on the hydro-carbon chain part of the molecule. When exposed to light and oxygen, bonds form between doublebonds on adjacent molecules. This causes themolecules to link together forming a ‘skin’. Oil paintscontain coloured pigments mixed with these dryingoils — once the paint has been spread on a painting itslowly starts to harden as the cross-linking processoccurs.

16 Catalyst

Figure 3 The action of soaps and detergents(a) Dirt on cloth, detergent molecules in water(b) The hydrocarbon chain of the detergent prefers the dirt rather than the water(c) The dirt is lifted from the cloth as more detergent molecules repel each other(d) The dirt is removed and washed away

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The phosphates used in detergents end up in riversand lakes where they act as a nutrient for algae

Box 1 SoapwortSoapwort gained its namefrom the ability of its crushedroot to produce suds whenrubbed in water. It can beused as a mild detergent forfabrics. Soapwort was onceadded to beer to create afrothy head. The plant acts as both an antibacterial andan expectorant (it loosensphlegm, making it easier tocough up).

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A pigment is a colouredcompound which isinsoluble in water.

Oils as fuelsOils and fats can also be used as fuels. In the UK over1 million tonnes of rapeseed is produced each year.The oil from rapeseed cannot be used as a fuel on itsown — the long carbon chain part of the oil wouldburn readily, but the propane-1,2,3-triol residues thatform during combustion would clog up the engine.

Instead, the oil is boiled with an alkali to break it down and the mixture acidif ied; this allows thelong-chain carboxylic acid products to be isolated (see ‘Biofuels’ in CATALYST Vol. 17, No. 1). They arereacted with methanol to produce methyl esters[CH3OC(O)R]. It is these methyl esters that are usedas fuel.

Rape methyl ester is a good diesel substitute whichhas several environmental advantages over conven-tional diesel fuel. It does not form sulphur dioxideand emits fewer sooty particles during combustion.

MargarineMargarine is used as a substitute for butter. It is madeby hardening fish and vegetable oils. The process useshydrogen in the presence of a nickel catalyst. Duringthis process double bonds in the hydrocarbon chainbecome saturated, turning it from an alkene into analkane (Figure 4). This makes the oil become harder.Semi-soft margarines, which are ‘high in polyunsatu-rates’, are made by mixing untreated oils with those

that have been partially hardened. Polyunsaturatedfats are thought to be less harmful to the heart andarteries than saturated fats.

David Moore teaches chemistry and is an editor of CATALYST.

17November 2006

Figure 4 Adding hydrogen to a double bond

C CH2 + C C

H H

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Margarine is oftencoloured using carrotextract.

Fats containingcarbon–carbon singlebonds are said to besaturated, thosecontaining doublebonds are said to beunsaturated.

Box 2 Useful websitesl Find out more about whaling at:http://en.wikipedia.org/wiki/Whalingand for the current position on whaling look at thesection for the International Whaling Commission.l Find out more about the history of soap at:www.pjonline.com/Editorial/19991218/articles/soap.htmll There are more details on soap and detergentmanufacture at:www.cleaning101.com/cleaning/manufact/l These two sites highlight the problems that arisefrom phosphate use:www.wwf.org.uk/news/scotland/n_0000001573.aspwww.swissinfo.org/eng/swissinfo.html?siteSect=43&sid=5008242

Rapeseed is obtainedfrom the yellow-flowered rape crop that can be seen in early summer in the UK countryside.

PuzzleWordmaze

Answers on page 19.

Plants (e.g. sunflowers) can be used as a source of oil, butthey can also be used for medical and culinary purposes.Fit the plant names listed below into the grid. The end ofone word begins the next. The beginnings and endingsare highlighted in yellow. Start with the word ‘Sunflower’in the top left, and move round in a clockwise direction.Once you have managed to fit all the words into the grid,rearrange the letters highlighted in green to form thename of a herb which is often used in sweet making.

5-letter wordsELDEROLIVEBASIL

6-letter wordsYARROWENDIVESPURGEERYNGO

7-letter wordsRAMPIONANISEEDRHUBARBRAMSONS

8-letter wordsLAVENDERSAMPHIREROSEMARYANGELICA

9-letter wordsSUNFLOWERDIGITALISSANTOLINASAFFLOWER

10-letter wordsELECAMPANEWATERCRESSEUCALYPTUS

Hurricane, typhoon, cyclone — these are allnames for the same thing, a violent tropicalstorm. Winds spiral round a central ‘eye’ at

speeds of over 300 km/h while torrential rains pourdown.

How do hurricanes form?Hurricanes form in two bands around the Earth,usually between 10° and 20° to the north or south ofthe equator (Figure 1). In these areas, sea water iswarmed by the sun so that it reaches the criticaltemperature of 26°C. A convection current of warm,moist air rises above this water. As it rises, it coolsand water vapour condenses as rain, releasing energy.Just as it takes energy — known as latent heat — toevaporate water, so this energy must be released whenthe vapour recondenses.

As a hurricane tracks across the ocean, more moistair is sucked upwards at the low pressure eye, provid-ing a constant source of energy (Figure 2). Hurricanesgradually lose energy when they move over landbecause there is no warm, wet air to keep them going.

18 Catalyst

HurricanesDavid Sang

GCSE key wordsWater cycleConvection

Condensation

In August 2005, Hurricane Katrina causedmany deaths — and vast damage — along thecoastline of the Gulf of Mexico in the USA.Hurricanes are an unfamiliar phenomenonhere in the UK. Why is this? And can weexpect to see more hurricanes in future as aresult of climate change?

Aug–Oct‘hurricane’

Jan–Mar‘tropicalcyclone’

Jan–Mar‘tropicalcyclone’

June–Nov‘typhoon’

Equator

Eye Rain bands

Air spirals upwards, cooling;moisture condenses

Warm, moist air drawn in

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Figure 2 Cross-section of a hurricane

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Figure 1 Map of zones, directions and seasons

The first hurricane ofthe season is given aname starting with A;they then work throughthe alphabet. Once ahurricane (like Katrina)has become famous,this name will not beused again.

l Look out forhurricane warnings atwww.hurrwarn.com

19November 2006

Why do hurricanes form a spiral?The spiral arises as a result of the rotation of theEarth. A hurricane tends to move towards the west, inthe opposite direction to the Earth’s rotation. Therotation causes the hurricane to be flung off to oneside, northwards in the northern hemisphere andsouthwards in the southern hemisphere. This makesthe winds spiral round, and pushes the track of thehurricane away from the equator. This is known asthe Coriolis effect, and explains why hurricanes donot form over the equator — there is insuff icientsideways push.

The winds spiral in towards the low pressure atthe eye of the storm. As they do so, they speed up.This is similar to the way in which spinning ice-skaters can speed up by pulling their arms in to theirsides. It is an example of the conservation of angularmomentum.

How are hurricanes classified?Hurricanes are classified according to wind speed (seeTable 1). Table 1 also shows the height of the stormsurge that results as the circling winds cause the sea topile up — this rise in sea level may do as much damageas the winds themselves when it makes landfall.Although the UK is far off the regular hurricane zone,many people still recall the storm of September 1987when hurricane force winds crossed much of southernEngland.

Can we expect more hurricanes in thefuture?This is a question which divides scientists. First, it isimpossible to attribute a single hurricane (e.g.Katrina) to global warming. There have always beenindividual, devastating hurricanes. Similarly, anincrease in the number of hurricanes from one seasonto the next may be part of a natural cycle, rather thana growing trend.

However, some scientists claim to have found anincrease in the frequency of the most violent storms —these have doubled in the last 30 years. This may be asignificant change.

Another analysis suggests that there is a strongcorrelation between the surface temperature of theoceans and the number of hurricanes. As the oceanswarm up, the hurricane zones may extend furtherfrom the equator and be active for more months ofthe year.

l In Britain tornadoesare more likely to affectus than hurricanes. Findout more abouttornadoes in Britain atwww.torro.org.uk

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Devastation caused by Hurricane Katrina — 12 monthslater, half the population of New Orleans were stillunable to return home to their devastated city

Table 1 The Saffir-Simpson scale

Wind speed StormCategory (km/h) surge (m) Effect5 ≥250 >5.5 Buildings collapse; severe flooding4 210–249 4.0–5.5 Extensive damage to buildings;

beaches eroded3 178–209 2.7–3.7 Structural damage; flooding near coast2 154–177 1.8–2.4 Some damage to buildings; trees down1 119–153 1.2–1.5 Minor damage to shrubs and

trees; some flooding on coastTropical 63–117 0–0.9 Limited damagestorm

Herb used in sweet-making: Licorice

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Answers to wordmaze, page 17

Before 1979, hurricaneswere given only girls’names. This wasdeemed unfair so boys’names were added.

Y ou have probably seen fruit flies — they are thetiny yellowish f lies that rise up when youdisturb rotten fruit. You may even have been

fortunate enough to have used fruit f lies to tracksimple patterns of inheritance in breeding experimentsin biology lessons.

In hot weather, the life cycle of the fruit fly (seeFigure 1) may take only 7 to 8 days and the adult lays700 to 800 eggs in its 20- to 30-day life span. Oncethe eggs hatch, the maggot-shaped larva burrows intothe fruit. Oblong pupae with a forked breathing tubeat one end occur wherever larvae are found.

It has proved relatively easy to recreate optimumconditions for fruit flies in laboratories and to main-tain them in captivity under controlled conditionsfrom one generation to the next (see Box 1).

Useful fliesDrosophila has a long history as a model for geneticstudy. Research began on the fruit fly over 100 yearsago when the biologist Thomas Hunt Morgandiscovered a mutant fly with white eyes (see Box 2)rather than the normal red eyes. Drosophila quicklybecame one of the most important organisms used ingenetics research, not only in terms of patterns ofinheritance at the level of the chromosome and thegene, but later on at the molecular level, in terms ofDNA and protein structure and function. It has alsoproved useful in looking to see how a complexorganism develops from a relatively simple fertilisedegg.

In 2000, the Drosophila genome was sequenced — itis reckoned that 61% of known human disease geneshave a recognisable match in the genetic code of fruitf lies, and 50% of the amino acid sequences in f lyproteins have mammalian matches.

Researchers have found that many aspects of thebiochemistry of fruit flies and humans are similar.Because of this, fruit flies have become a useful tool in

20 Catalyst

A life in science Drosophila

melanogasterWe normally focus on people in this column,but this issue we are looking at an organismthat has played a succession of key roles indevelopments in biological science over thelast 100 years — the fruit f ly, Drosophilamelanogaster.

Figure 1 The life cycle of Drosophila melanogaster

Female Male

Embryo

1st instar larva

2nd instar larva

3rd instar larva

Prepupa

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Genetic research. Abiologist holds a milkbottle in which normaland mutant fruit flies ofthe species Drosophilamelanogaster are raised

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studying human diseases caused by defective genes,including Parkinson’s, Huntington’s, Alzheimer’s,diabetes and cancer (see pages 1–3).

ConclusionThe story of the fruit f ly is an interesting one. The more people found out about the organism, theeasier it became to work with. As a result, more

researchers were attracted to it and more techniquesand deeper levels of understanding were developed.Today, Drosophila is found in laboratories around the world and is the subject of intensive study by a large research community of several thousandscientists.

Nigel Collins teaches biology and is an editor of CATALYST.

l If you have a safeplace to set up a plasticcontainer out of doorswith some overripe fruit— it will need to be insummertime — look outfor fruit flies.

21November 2006

Box 1 Culturing and countingDrosophilaFruit flies are obtained easily from the wild andcompanies stock a variety of different mutants. It isnot difficult to keep Drosophila. They can be kept inlarge numbers in small jars, with some food and acotton wool stopper. The cotton wool preventsthem from escaping while allowing air movement.They can be fed with a mixture of dried yeast, sugarand cornmeal, thickened with agar.

At 25°C it takes Drosophila only 10 days to gofrom egg to adult. The life cycle can be completedwithin 2 weeks. The resulting large populationsmake statistical analysis easy and reliable.

Drosophila can be anaesthetised, using a stream ofcarbon dioxide, to count and sort different typesunder a microscope. They recover rapidly. Themales and females are different in appearance.

Over time, more and more mutants have beenfound or created. In the days of classical geneticstudies these differed in appearance. Nowadaysmutants may have differences that are revealed only through biochemistry, with individual genesaffected — so called ‘knockout’ flies. For breedingexperiments, virgin males and females are oftenobtained by separating the sexes as soon as they hatch, though they can be separated laterbecause virgins are physically distinct from mature adults.

Box 2 Thomas Morgan and DrosophilaThomas Morgan and three of his students wereinterested in what we would today call classicalgenetics. By doing controlled crosses with differentmutants, they were able to show that certaingroups of genes were linked together. The numberof linkage maps produced tied in with the numberof chromosomes, helping to identify chromosomesas carriers of hereditary material.

In 1915, Morgan and his students summarisedtheir work in a book, The Mechanism of MendelianHeredity. Morgan was awarded the Nobel prize formedicine in 1933 ‘for his discoveries concerning therole played by the chromosome in heredity’.

Morgan and his colleagues also discovered howgender was inherited in fruit flies. By coincidence,the same system occurs in humans, involving X andY chromosomes. The white-eyed flies showed sex-linked inheritance. The eye colour gene is locatedon the X chromosome, with no matching positionon the Y chromosome. If a recessive white-eyed alleleoccurs on the X chromosome, a male fly has whiteeyes. For females (XX), one chromosome may carrythe red-eyed dominant allele.

In 1995 Ed Lewis, Christiane Nusslein-Volhardand Eric Wieschaus were awarded the Nobel prizein medicine/physiology ‘for their discoveriesconcerning the genetic control of early embryonicdevelopment’, using Drosophila.

The Drosophila genomeis about 165 millionbases and contains anestimated 14 000 genes.The human genome isabout 3000 million basepairs and involves anestimated 30 000 genes.

l Find out more about Drosophila atwww.ceolas.org/fly/intro.html

l Read more aboutThomas Morgan and the other Nobelprizewinners at:http://nobelprize.org/nobel_prizes/medicine/laureates/

Left: A normal and amutant fruit fly. The flyon the left, with thered compound eyes,is the wild type. Thefly on the right is amutant type. It haswhite eyes, shorterwings than the normalfly, and the bristles onits face and body aredistorted and forked

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The allotropes of carbon — diamond, graphite andbuckminsterfullerene (bucky balls) — are well known.

Now scientists are working on buckytubes (Figure 1).Buckytubes are based on elongated tubes formed fromsheets of hexagonally-linked carbon atoms, capped atboth ends with carbon pentagons. These tubes can be aslittle as 1 nanometre (10–9 m) in diameter. Althoughscientists have known about buckytubes since the 1960s,it was only in 1992 in Japan that Sumio Iijima firstmanaged to make them in large quantities.

The tubes form without defects in their structure. This isunlike any other known material — steel, for example, failsat about 1% of its theoretical breaking strength due todefects in its structure. They can be manipulated chemicallyand physically and have unique properties which cannotbe bettered by any known substance. They offer amazingpossibilities for creating future nanoelectronic devices,circuits and computers.

Properties of buckytubesl Electrical conductivity — they are as good at conducting as metals — better than any other polymer. They can carry the highest current density of any known material. A different form of buckytube acts like a semiconductor.l Thermal conductivity — they are twice as conductive as diamond — previously the best-known thermal conductor.l Mechanical properties — they are the stiffest known fibre— stronger even than high tensile steel.l Chemistry — they have been filled with molten lead,leading to the idea of molecular wires. They have also beenfilled with proteins and catalysts. Substances can bechemically bonded to their ends or to their sides, leading tothe possibility of all sorts of new technological applicationsin the future.

CylindersIn addition to having a single cylindrical wall, nanotubes can be made which have multiple walls — cylinders insideother cylinders. Sheets can also wrap around each other inspiral fashion to form a hollow cylinder with a core of up to15 nanometres wide.

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Coloured transmission electron micrograph of the world’ssmallest bar magnet — a single crystal of nickel inside ananotube

Activitiesl Move a buckytube around in three dimensions at:www.3dchem.com/molecules.asp?ID=104l Find out more about buckytubes at:www.pa.msu.edu/cmp/csc/nanotube.html

Figure 1 Buckytube