Practica\5.2 The effect of temperature on the hatching success of brine shrimps

Practica l 6.1 DNA gel electrophoresis

Practica\ 6.2 DNA amplification using PCR

Practica\6.3 . Which .~ntiblot!c is most eftec.tive? Practical 7.1 Measuring the rate of oxygen uptake Practical 7.2 Investigating breathing

Practica l 8.1 Can snails become habituated to a stimulus?

Practical Ecological sampling support sheet

Practical 5.2 The effect of temperature on the hatching success of brine shrimps

Practica\6.1

Practical6.2

Practica\6.3

Practka\7.1

Practica\7.2 Practical 8.1

Unit 4 Topic 6

Unit S Topic 7

Unit 5 Topic 8

DNA gel electrophoresis

DNA amplification using PCR

Which antibiotic is most effective?

Measuring the rate of oxygen uptake

Investigating breathing

Can snails become habituated to a stimulus?

10

11

13

15 ,.,.---'-,.

16 18

22

23

23

26

31

33

34

35

37

39 43

45

45

50

57

62

TopicS Topic 6

Topic 7

TopicS

Practical 5.1

Practical5.2

Practical 6.3

Practical 7.1

Practical 7.2

Practical8.1

looking for patterns

The effect of temperature on the hatching success of brine shrimps

Which antibiotic is most effective?

Measuring the rate of oxygen uptake

Investigating breathing

Can snails become habituated to a stimulus?

104

120

134

151

151

152

153

154

155

157

Edexcc!A2 Biology are Edexccl's own support materials for a concept-led approach to delivering the Edexcc\ A2 Biology specification . Complete support is provided from the following resources:

A2 Students' Book with FREE ActiveBook CD-ROM Supporting student's learning by providing step-by-step coverage of the specification helping students to develop a scientific understanding, including How Science Works.

Examzone sections provide real Ed excel exam practice questions and allow students to regularly test themselves and prepare for assessment.

'The ActiveBook, featured in the back of each Students' Book, is an easy-to-use digital version of the Students' Book, with direct links frOm the pages to additional resources.

A2 Implementa"tiOii. and ASsesSment Guide for Teachers and Technicians

Provides everything required to deliver the core practicals within the A2 Biology specification, including student worksheets and notes for teachers and technicians.

Further assessment support is supplied including specimen tests developed from past Edexccl exam questions and answers for all the questions in the student book.

A2 Active Teach

Brings the specification to life with links directly from the student book page to enlightening animations and stimulating videos . Active Teach also integrates directly into c-Spcc, Edexccl'~ own digital specification, allowing users to follow links from the student book directly to the specification.

A complete set of equivalent resources arc also available from Edexcel to support the AS component of the specification .

Edexccl ab;o provide materials for the Saltcrs-Nuffield Advanced Biology approach to Ed excel GCE Biology, providing a context-led approach to the specification.

For more information or to order further resources, please call FREE on 0800 579 579 or visit www.edexccl.org.uk/GCE2008

Safety \Vc have attempted to identify all the recognised hazards in the practical activities in this guide, provide suitable warnings about them and suggest appropriate precautions . Teachers Bnd technicians should remember, however, that \vherc there is a hazard, the employer is required to carry out a risk assessment under either the COSHH Regulations or the Management of Health and Safety at Work Regulations. Most education employers have adopted a range of nationally available publications as model (general) risk assessments and, where such published assessments exist for the activity, our advice is believed to be compatible with them. Nevertheless, teachers and technicians must check whether what is proposed is indeed compatible with the requirements of the employer. In a few cases

~ ~. Even where an activicy is broadly' in line with a model risk ass~ssment, staff in a school will still need to consider whether their particular situation requires any adaptation. We have assumed that practical work is carried out in a properly equipped and maintained laboratory and that any fieldwork takes account of the employer's guidelines. In particular, we have asswned that any mains-operated electrical equipment is properly maintained. that students have been shown how to conduct normal laboratory operations safely (such as heating or handling heavy objects) and that good practice is observed when chemicals or living organisms are handled. We have also assumed that classes are sufficiently small and well

~ehaYed for a teacher tO be able to exercise adeQuate supervision of the students and that rooms are not so crowded that students' activities pose a danger to their neighbours. Members of the staff of CLEAPSS have read the practical notes and Worksheets in this guide. In the draft that was checked, the health and safety reviewer gave guidance on how to make this text conform to the above policy, and such recommendations were incorporated before publication .

A brief statement such as this can only be a sununary. Any guidance issued by your employer must be followed, whatever is suggested here.

---- - ----- ---- - --- ------------- - - - - - -------------- - --------- -"

To carry out a study on the ecology of a habitat.

Teachers/lecturers must follow their LEA/schooVcollege policy and local rules for off-site visits, especially with regard to ident ification of hazards and risk assessments. Additional infOrmation is available in the DCSF guidance Health and Safety of Pupils on Educational Visits on the Tcachernet website. The haza rds will vary depending on the site chosen. Risk assessments will identify the risk,

Notes on the procedure Students need to carry out a study on the ecology of a habitat to produce valid and rcliabk d3.ta (including the use of quadrats and transects to assess the abundance and distribution of organisms and the measurement of abiotic factors). This activiry outlines how to approach a fieldwork investigation. It briefly mentions some techniques that might be.used . It does not attempt tO provide detailed accounts of the techniques . Ad ditional details are provided on the Srudent Practical support sheet Ecological sampling (page 26) and there is a wealth of information on the British Ecological Sociery student 16+ education web pages abou t sampling techniques. There are also examples of projects with data and virtual tours of the rocky shore and sand dune h-...biw.ts. The Field Studies Council website also h

~===-==-=-=~------ -

a u:oodlaud margin- passing from a field or other example of grazed or mown grassland, through brambles into a wood ."Illc key gradient is likely to be light intet:tsity- but it may not be the only one. a saud dune sy1rem from the shore across dunes into gra5sland and scrub as you go further. inland . In this case the key factors could be soil moisture, soil stability and organic matter, although succession is also involved here. a rocky shore from the low tide mark to the top of the beach. The key factor is the proportion of time a part of the shore is le ft exposed to the air and to desiccation when the tide is ouc a geologica.! boundary between two types of rock, such as between limestone and millstone grit.

Some examples where two sites can be compared:

grazed and ungrazed grassland mowed and unmowed grassland

trampled and untrampled grassland

fertilised and unfertilised lawns

shaded and sunny sites fast- and slowOowing streams

chalk and sandy soil sites

understories of beech and oak woodlands.

The two sites could be compared by random sampling.

Identification - don't panic! Identification is not as big a problem as you may think. T he only species students need focus on are those which would support the hypothesis under investigation . Trying to identify each species in a quadrat down to the tiniest piece of moss can be a poor usc of time and can actually prevent students from 'seeing the wood for lhe uecs'.

A transect at a woodland margin could be successfully done recording only tree cover, grass, brambles, nettles, ivy, bare ground , wild garlic (with give away smell) and bluebells, together with good light meter readings and soil pH (often showing no pattern), especially if you stan to consider something like leaf surface area of brambles :n the same time.

But the. principles arc: select a site where students can cope with the ~pecies. identification before tcachin{1 students to identify another species, ask yourself '\X'hat is t}:_~ ecological point of teaching this?' make usc of expert help if available- this could include a Field Study Centre .

T he r:'icld Studies Cou ncil produces excellent laminat ed cards to aid with field identification in particular habitats .

The students will be relying on you for identification so careful preparation is imponam.You may like to produce a record sheet that includes the species you want to fOcus on.

Class organisation Students can work in groups if they are not using this investigation for their A2 courscwork. The smaller the group the more 'ownership' by individuals, whilst the luger the group the more quadrats can be recorded and the bigger and statisticc.lly more meaningful the picrure that can be produced. A good group size is six- working as three pairs. It helps if the whole group can have access to a computer as soon as possible after collecting the data and to a full set of equipment during data co\lcr.:tion. Waiting to borrow equipment from other groups wastes a lot of lime and loses momentum .

P2cc is also imponam- it is possible to be too slow and nit-picking about accuracy, in which cnse the students become bored and lose sight of the bigger picture. his also possible for the students to feel it is somehow 'efficient' to get the job done as quickly as possible, subsequently data are produced tl1at are so inaccura te and incom plete that they do not produce reliable results.

FieldWorks: an invaluable IT resource Field Works is available on CD and produced by Interp retive Solutions, 1--Iallsanncry Field Centre, Bideford, Devon EX39 SHE. It benefits from having grown out of the lcarnlng experiences of many students.

Students can enter their own dat?., and present these using kite di agrams or mher formats. It also contains information about species and habitats including rocky shores, sand dune, salt marsh, moorland, woodlands and fresh water .

The dal'a can be subjected to statistical analysis using correlation coefficients (Pearson's parametric or Spearman rank non-parametric), particularly useful with transects. Tile programme can also calculate species _diversity indices and car~y out Hests and z-tesrs.

Other statistical packages are available for usc in ecology from sofnvare companies and oilier suppliers.

Useful references

]ones C. (1998) FieldwOrk sampling- animals. Biological Scimces Rf!victv, 1 0(4) , 23- 25 . Jones C. (1998) Fieldwork sampling- plams. Biological Sciences Re-vieu, 1 0(5), 6-8 . \Vi\lia ms G. (1987) 1Cchniqucs andflcldU'ork in ecology. London: 1-brpcrCollins. Field Studies Council identification sheets and booklets are very good. These can be obtained from: FSC Publications, Preston Montford, Montford Brid ge, Shrewsbury SY4 1HW.

. ---------- --.--- - ------ -- -- ------- - --~

To inve~tigate the effect of temperature on the hatching success of brine shrimp. To develop certain experimental skills, namely considering the ethical issues arising from the use of living organisms, presenting results, produdne reliable results, identifying trends in d2ta and drawing valid conclusions.

Notes on the procedure If students arc given basic information on maintaining brine shrimps this activity could be planned before they are given the Student sheet. The need to keep conditions other than temperature constant should be appreciated. Brine shrimps hatch in salt water that is 2 to 5% sal t (optimum 2.8%) and pH 8.5 . Oxygen must be present. Light is an added (but not essential) factor for hatching. b atalogging could be used to 'check that the conditions within each of the treatments arc maintained at a constant level.

TI1is experiment could be completed by small groups of students. lf each group completed the range of temperatures then the error between replicates could be investigated. Brine shrimps will hatch in 24 hours at temperatures between 25 and 30 C with an optimum of 28 C .

This acti,,ity can be used tO highlight cxpcrimcmal and ir.vestigativc assessment objectives, in pat ticular th~ ethical issues arising from the use of living organisms (including the disposal of the brine shrimps after the activity) and for the emironmcnt, and the need to identify both depend ent and indepe ndent variabks and, where possible , control or allow for them. 'TI1::: method suggested provides precise measurements. The need for valid, .reliablc results should be considered and the random nature of error could be investigated .

The practical procedure and technical notes are based on an investiga tion that appears in the British Ecological Society publication Bri11e Shn'mp Ecology by Michael Dockery and Stephen Tomkins. This book contains detailed information on the care and breeding of brine shrimps. h is availab!e from the British Ecological Society or from:

Homer ton Brine Shrimp Project Dept of Biological Sciences J !omen on College Cambridge CB2 2PH Td: 01223 507175

Price from Blades Biological, 48 .26 (2009} including post ;md packing, brine ..... shrimp cges Hnd innoculum

For m ore details, including the preparation of a salt water ~tquarium in which to keep the brine shrimps , sec the teacher area of the British Ecological Society website.

fragments of different sizes. Jationa! Centre for Bicto::chnology Education) and Bio-Rad. Pro tocols fo:- lhcse practicals as pdf files can be downloaded from their \vebsites .

~CBE produce an electrophoresis base unit and a lambda DNA kit. Together these contain all necessary gel electrophoresis apparatus, dried lambda DNA, three dried restriction enzymes and both student and technical guides. TI1c kit includes microsyringcs and gel tanks but not bancries needed as a power supply.'l11c kit for eigh t d c:ctrophoresis stations (16 runs) cost 52 in 2009.11le lambda protocol module, for usc with eight students, cost 90 in 2009.

Have a look at the technical guides by downloading the pdf l1\cs from the N CBE website .

The N CBE publication l\luminating D NA also contains protocols for expcrimmts using rcstiiction enzymes and elecuophoresis. This publication can also be viewed on the NCBE website.

N CI3E has developed a genet.ic screening simulat.ion, Nature's dice. In this practical simulation, th.e inheritance of a single gene that is involved in a particular genetic trait is investigated . The kit contains 24 D NA samples donated by a large family who arc affected by Li-}e genetic condition.

Each student is given one or more of thl!se DNA samples and they have to detect which allele is present . 'll1cy cu t the DNA with n restriction enzym e and examine th e resulti ng DNA fragments by electrophoresis. The genetic data obtained is tl1cn combined \vit..h the family tree to look at l_1ow the genetic trait is inherited .

This ncti\'ity would provide :m excellent altcrna\ivc to the standard gel electrophoresis practical suggested above . Further information 11bom the kit and cost of mtcrials is on the websi~c listed in the web! inks section for this activity.

Bio-Rad produces a Rcstrict.ion Digestion and analysis of lambda DNt\ J.:.it. rfnis contains dried lambda DNA, three restriction cn

Plil-er and llio~HaJ h3\c lionatcd biotechnology equipment to 31111 centres around the country as pan of a Kationa!Ycu of Science project. Each cr:ntrc holds equipment 1hat can be used to conduct biotechnology practica\s for 25 students at a time . They have all the cquipmcm necessary for completing DNA fingerpriming 1 bacterial transformation (genetically altering bacteria wiu, ~ bioluminescent jellyfish gene), purification of a useful protein, and L,e polymerase chain reaction (PCR). 1t is envisaged !.hat this equipment will be used for hamls~on practical uaining of studcuC science teachers. There arc also plans for loan schemes to be established to enable local schools to Darrow t.l,e equipment. To find out more about this project contact the 13ioEducation Project 1\-\anagcr at Bi o~Rad Laboratories (details can be found on the Bio~ Rad website).

Both organisations produce replacement equipment for their kits and also supply the components separately.

Note that some of !.he Bio~Rad manuals accompanying their kits (unless recently revised) may not carry fuU and app;opriatc health and safety guidance applicable in the UK (t11ey were written for a US audience). \Vhere the instructions conflict with good practice that is standard in the UK, additional precautions should be taken.

It is most likely that gel electrOphoresis equipment using batteries or a low~voltagc supply is used. This is safe_ if the volt2ge is less than 40V DC. If equipment is used that is opermed by a power supply at a greater voltage, it is essential that the equipment is designed so that it is impossible to make skin contact with the electrodes or ckctrolytc when an electric current is flowing. rnis is usually achieved by a suitable design of lid for the gel tal".k which only permits a current to ftow when the lid is in place.

Also, although it is very unlikely to be needed 1 elhidium bromide, which is very toxic 1 is not normally recommended for use in schools.

For general CLEAPSS guidance on e\ectrophoresis1 schools should consult section 11.1.7 of the Laborawry Handbook.

PCR

should be obtained for the procedure and carefully foHowed by both staff and students.

It is possible to carry out practical PCR Using equipment available from a number of suppliers including NCBE (N'atiOnal Centre for Biotechnology Education), Bio-Rad and EdYotck Europe. Although all crga""!isatiC'ns supply automated PCR t.'-lcrmal cyclers, they arc not absolutely necessary. Instead , PCR can be undertaken using three separate thermostatically controlled water baths, although care must be taken with the honest as a risk

of~calding exists. Note that during Science Year (Septcmber.200l-}uly 2002) many schools, colleges and initial teacher training institutions received free PCR equipment.

Student and teacher/technician protocols for the PCR practicals can be downloaded as pdf files from the suppliers' websitcs.

Equipment can be purchased either in class sets or indi,~dual!y, with consumablcs al so available in class-sized batches. All three organisations listed offer training courses, frequently in association with other instirutions like botanic gardens or science centres, giving icachcrs and technicians the opportunity to carry out the practica\s themselves.

There are social and ethical considerations to take into account \vhen using DNA derived from students for PCR. Although the suppl iers should have chosen STR sequences that have no biological significance, it may be socially and ethically Jess challenging to usc plant DNA as the sample. But working with one's Own DNA can be uniquely motivating!

Educcl pr~ctic~ l maoeri~b cre~:ed by S21!tr~Nurfodd ,\dvanced Biology, C: Un.hcnirJ of York Science Education Group

Contact details and examples of the protocols offered by NCBE, Bio-Rad and Edvotck Europe:

Organisiltion

NCBE Nat ional Centre for Biot echnology Education Science and Technology Centre The University of Reading White knights Reading, RG66BZ \NW\v.ncbe.reading.ac.uk 0118987 3743 NCBE@reading.ac.uk

Bio-Rad Bio-Rad laboratories Ltd. Bio-Rad House MaxtedRoad Hemet Hempstead Hertfordshire HPZ ?OX www.biorad.com/ Follow the \inks to Life Science education, then About Biotechnology Explorer Freephone:OBOO 181134

Edvotek Europe The Biotechnology Education Corf1pany PO Box280 Hertford SG139DG www.edvotek.co.uk Follow links to Experiments and then Polymerase chain reaction ukinfo@edvotek.com

Example of suitable protocOLs

Amplifying lambda DNA (from the Illuminating DNA booklet) investigating plant evolution Analysing mitochondrial DNA. This prac tical requiresamicrocentrifugeand theprotocol isnot down!oadab\e from the NCBE website. It is based on a protocol developed for a DNA workshop at t he Cold Spring Harbor Laboratory. It can be obtained di rectfromNCBE.

Crime ~cene investigator- PCR basics PV9Z PCR infomatics kit GMO investigator kit (only usef_ul if GM foodstuffs are easily available)

332 Mitochondrial DNA analysis using PCR

Ed~xc~l P~c:ol materi:ols cr~atcd by Salters-Nuffidd AdvanC(d Biology, OUnicrsity of York Science Education Group.

I .

r difierent antibiotics on bacteria. work, though it is good standa rd practice.

The r:nicroorganisms are a potential biological hazard. Use aseptic techniques when transferring the bacteria to the Petri dishes. Clean the bench with antibacteri al disinfectant. Do NOT open the Petri dishes once they have been incubated.

Notes on the procedure Tnc aim of the practical is to show students a method of determining bacterial sensitivity to different antibiotics and to give them practice at using aseptic tech.niques.111is could be done with antibiotic discs or the same technique could be used With antiseptics. The Student sheet suggests using different bacterial species but the activity could be done using just one species. However, using different species should illustrate that they are not all equally susceptible.

Although allergic response by patients is considered in the questions, where antibiotics are aircady impregnated on to discs, the risk for students with al!ergic responses is not great. Discs are not handled directly and no airborne dust is created by the discs.

The bchaYiour of students must be considered. lf d1cy might attempt to lift a piece of mpc from an incubated dish, U:e agar plates should be sealed around the circumference af/er incubation but before being returned for observation. Also, to prevent agar plates being removed from the lab, count all plates back in again before students are allowed to leave.

Answers 1 Choice of strategy may vary, but it must be dear and easy to carry out and produce

reliable results.

2 Tne rate of di ffusion of the antibiotic will be influenced by the size of molecule , its concentration and the potency of the antibiotic. If the antibiotic is effttctive at lower concentrations the ~ir-:::lc will be larger (aU other things being equal). Gram-positive and Gram-negative bacteria respond differently to antibiotics.

3 Responses will depend on the data, but should show a clear undcr::nanding of the concepts of accuracy, validity and/or reliability when explaining variation . Suggestions for the presentation of variation in graphs may also vary but need to identify anomalous results dearly so that coriclusion are obviously based On reliable results.

4 You'TTlay have to consider whether the patient is allergic to any of the antibiotics. for example, allergy to penicillin is not uncommon.You may consider the state of the patient's immune system. In patients wiLh. a weakened inunune sys!em you would not want to use a bacteriostatk antibiotic, that is, one that slOps bacterial reprodm.:tion but docs not kill the bacteria. Some antibiotics can be used together and produce ::1 larger effect when combined than if administered separately. This is known as synergism.

Ede~ce! p~ctica! m~ter;au crta!ed by S:t!ltrs-NWfie!d 1\dl~ced Biology, OUrJenily of York Scicnct Educ~tion Group.

respiration. To measure the rate at v.ohich an organism respires_

Soda lime is corrosive. Do not handle direct ly: use a spatula.

Notes on the procedure Rate of respiration is not a learning outcome in the specification. The respirometer shown in the diag ram is a very simple one; more complex ones (e.g. U -tubes) can be used if available. Question 1 can be used as a summary activity for student understanding of respiration if studenis arc askcd to complete it in as much detail as possible and to statc the source of carbon dioxide as well as its fate.

T he choice of what respiring organisms to put in lhe tubes is left to you. Germinating peas, maggots or woodlice are commonly used.

If you are using pipettes there is no need to do any volume calculations; students just read the change in volume off the scale on the pipettes. If you are using thick w:alled capillary tubing it is worth reminding students of the formula for worlcing out the volume of oxygen used, and explaining it again.

volume of oxygen used = -;rr-2 X distance mo\ed

where r = the radius of the capillary tubing or pipette.

Three-way taps can cause confusion with some students. A diagram of how the three-way tap works is shown in lhe diagram below. Putting up an OHT of this diagram during the practical can help.

resf1irometeropen to syringe

respirometer open t oatmo~phere

Tap polifionsfor 1 three-way tap (vit>wtd from th e side)

E..l excd poctiQ! m~ teriah cre> ttd by s~l!c r s-Nufflcld 1\d"anced Hio!ogy, OUnil"trli ty of Ymk Science Education Gtoup.

res pi rometer isoi.Jted

1 I

Answers 1 Simple answer: Oxygen molecules are absorbed by the organism and used in respiration. The

same number of carbon dioxide molecules arc released but these are absorbed by the soda lime. 11l.is reduces the pressure inside the test tube (fewer molecules = lower pressure}. Atmospheric pressure pushes the liquid along the rube, until the pressure in and outside the tube is equal. Detailed respiration review answer: As above but should include reference to the role of oxygen as the final electron acceptor, and the fact that it cvcnrually combines with hydrogen to make water. The carbon dioxide comes from the carbon dioxide released in t..l,c link reaction and the Krebs cycle as the carbohydrate is broken dov.'l1.

2 a A drop in tcmpernrurc inside the rube, or an increase in aunosphcric pressure. An increase in temperature inside the tube:, or a decrease in atmosphc::c prcssu:-c.

c The distance moved by the liquid in the control in each minute towards the organisms should be subtracted from the distance that the liquid in the experimental respirometer moved. Movement of the liquid in the control away from the organisms should be added to the distance in the experimental tube.

3 Diagram shO\.,.mg a very simple respirometer:

Disadvantages - does not allow you to reset; it needs a control rube used alongside it; no scale so measurements likely to be Jess accurate.

Advantages- \cry simple to set up; minimal nwnbei- of connections makes a good seal easier to obtain.

scr~wclip

dioxide mar.ometertube containing fluid

U-tuberespirometer

three-way tap

KOHsol utior.

Advantages- does not need to have an additional control as the second tube balances out the effects of changes in temperature or aonosphcric pressure; the syringe allows you tO move the liquid in the U to reset the apparatus. Disadvamages- tendency for the connections tO leak in elderly schooUco\lcge models (ma..lcing the equipment. useless); expense.

4 The cxp(:rimcnt.al design should include either aU-rube respirometer or controls; a known mass of maggots; a range of temperatures (bct\veen 5 C and 40C); a suitable increment between temperatures (say, 5C); repeated measurements (say, ar least three at each temperature).

Ed:xcel practical m~terials a ea. ted by Salters-Nuffield Advanced Biology, O Unil"ersit)" of York Science Education Group.

~ ~~-~--~-- ~ --~-- - -~---~~- ~-Qi!IIJJ

r

Spiro meters A copy of a spirometer trace is p rovided at the end of these notes, for use when there is ~o access to a spirometer or as extra data to interpret.

T he practi cal describes the use of a spiromete r with a kymograph. Alternati\dy a dataloggcr can be used with a traditional water-flllcd spirometer or with an airflow spirometer. A range of d iffcn:m types of sensors can be used and some alternatives are described below using a spi rometer with a dataloggcr:

If you have not got access to a spirometer, mca ~mrcmcnt of vital capacit)> and tidal volume can be carried out using breath volume bags. T hese arc a fraction of the cost of a spiromete r. H owever, they cannot be u sed for m easuring oxygen consumption.

A spirome t e r should only be used with supervision. Students with breathing or circulation (heart) problems or suffer fm m epilepsy should not use the spiromete r. Read the manufacturer's instructions and safety notes before using the equi pment. CLEAPSS guidance is in section 14.5.1 of the laboratory handbook. If the students are allowed to breathe thro ugh the spirometer for too long t hey can lose consciousness from lack of oxygen. limiting the time spent breathing t hrough the spirometer and carefully observing each st udent should prevent problems. When using oxygen and absorbing C02: maximum time 5 minutes: in any other situation: maximum time 1 minute. lf a student becomes less alert or has any feeling of suffocation they should stop immediately. Since th e \eve,ls of COz are kept low by the soda lime, the students won't be aware tha t they are running out of oxygen until it is potentially too late. Stop using t he spirometer at once if the student experiences any unusual breathing problems or feels dizzy or uncomfo rtable. (Asthmatics may use a spirometer if they are other'l'>'ise in good health.) A trained membe r of staff sho uld use an oxygen cylinder to fill the spirometer. lf only a few breaths are to be measure-d, then atmospheric air is acceptable instea_d. The subj-ect will feel some res istance to breathing when using a spirometer. Because of this they should not use t he spirometer while exercising. To invest igate the effect of exercise, readings shoutd be taken immediately ;~ fter exe rcise. If resistance to breat hing suddenly increases it may be due to valves in the spirometer st icking. If th is occurs the va lves may need to be replaced. After use, t he tubing from the spi rometer should be removed and placed in 70% ethanol, to disinfect the interna\ ribbed surfaces where microorganisms might remain.

Notes on the procedure Effects of exercise on breathing rate and volumes can be investigated using the spirometer. Although this is not detailed on the activity sheet, ~; tudcnts do need to be able to describe how to investigate the effects of exerci se o.n tidal volume an d breathing rate .

Ecl:.\cd prtt.tici-1 materi als cTc~tcd by S~ltctiNuiT!dd Ad,'llnccd D>ology, 0Uni>"cnity or York Sc ie nce Education G roup

Using a spirometer with a data logger One advantage of collecting the data electronically is that the data can be moved from the datal egging software to a spreadsheet or a word processing program. The data collected can then be made avai lable to srudents involved in the investigation .

Sensors such as motion sensors can be used to record the up and down motion of the air-filled spirometer lid .

A motion sensor can be mounted above the large top surface of the moving lid (sec below). As the lid moves up and down the change in distance can be recorded. Make sure the limits of the motion sensor are known an d the mi nimum recordable distance is available when the lid is at its closest to the sensor.

If known series of gas volumc:s is introduced into the spirometer, and the distance between the motion sensor and the surface of the lid is recorded, it is possible to produce a calibration curve of distance versus volume. Most datalogging soft\varc can convert distance measurements recorded by the sensor to volume data .

In a similar way, a linear motion sensor (e.g. rotary motion or pendulum sensor) can be attached to the spirometer as shown below. \Xfith a pendulum sensor, a string weighted _with a small counterweight can be run from the end of the lid over the sensor's pulley wheel. When the lid moves up and down, the string moves over the pulley. The sensor reco rds a changing distance or angle. Calibration relating the volume of gas in the spirometer tank to the sensor's reading will be required.

f:;:::;Jmotionsenso r

Carbon dioxide and oxygen levels in the spirometer lid can be datalogged . Monitoring lhese levels gives anolher safety check that the col absorber is working and that 0 2 \evc\s are not falling dangerously low.

Alternatively, many of the datalogging companies now produce an airflow spirometer which measures volume by integrating the now data over time. These devices are very lightweight, do not need carbon dioxide absorbers and do not need cylinders of medical oxygen (they use the oxygc:n from the atmosphere).

Ede~cel practical marerials created by Sah.rs--Nuffield Advaneed Biolo~Y. OUnh-..niry of York Sci_ence Edu

Answers 1 The -..:alucs here arc for the trace provided at the end of these notes. Obyiously if a

student's own trace is used u'1e answers may be different. a _Tidal \o\ume- betwc;::n 0.5 and 0 .8 dm3 Encourage students to take an avcmgc over

several breaths. b Vital capacity= 2.55 dm1 averaged over the two brear.hs. c Breathing rate= between 18 and 20 breaths per minute (depending on the section of

the &raph used). d JY1inutc ventilation = 19 breaths per minute x 0.65 dm3 = 12 dm3 min- 1

The rate of oxygen consumption determined from the trace at the c11d of these notes is approximately 1.0 dm3 min-1 for the first 30 seconds.

3 lf the subject had bccrt exercising, the rate of oxygen conswnption would be higher, so the slope would be steeper. The trace would also show that t.'1e subject was breathing faster and more deeply.

4 This question allows students to think through the practicalities of using a spirometer in an investigation . They should think about the type of exercise: it is easier to usc a spirometer immediately after running up and down stairs than after swimming or paragliding. They may also consider individual variation and sample sizes. They should also think about the limits imposed by the amount of oxygen available in the tank. Comments on the effect of the spirometer on the subject are also worLI-t encouraging - a spirometer often causes breathing to become slightly more laboured particularly with older models that have smaller diameter tubing .

The graph should show that breaths become deeper and more frequent after exercise, with a greater rate of oxygen consumption .

j +- ~ '- -1--: - : -+ ~ f-'-H-+~~t---,_: ~-c"c~ _,-:+-+!+-'!-, f-- i-l'C~-"-~'IIf-- 11+1'1

___ _ ,_ :-+--'- -H- -,- -Timtfmimiles

S;~mplereferen ce!piromf'l eru

Take care that th~:! stimulus causes no harm to the snails.

Notes on the procedure In this investigation students fmd out if habituation to a touch stimulus occurs in sr:.ails. A giant African land snail is best, but large garden snails can be used . The smdent sheet that accompanies this activity contains a procedu re for this experiment but studems could be asked to p!r:~ t.~e i:;vcsti6ation Ll-tcmsdves. TOe experiment is more reliable if snails arc handled little prior to the experiment, so avoiding them becoming habituated to stimuli . n,e completion of Spearman's rank correlation provides an ex tension to this activity. Tne null hypothesis to be tested would be: there will be no correlation between the number of stimuli the snail receives and d;c time taken for the snail to re-emerge. Further imestigations might include how long the habituation lasts, or how ha ndling prior to the experiments affects the resuhs.

Answers l As the number of ~timuli incn.:a~c, the time taken for the snail to re-emerge will d~.:crea~c

-a negative correlation.

2 Srudcms present the results as a scatter gr2ph , with dle number of stimuli on the x-axis, and the time taken to re-emci"ge on the y~axis. StUdents should make a simple ~tatemem, from Ll)cir results, .as to \'-'hether there appears to be a positive, a negative, or no, corrdation. There is a negative correlation - as the number of stimuli increase the time taken fo r the snail to re-emerge decreases. Students should make a reference to d1c data . With repeated stimulation, Ca2+ channels in t.hc presynaptic lnembnmc become less rcsponsi\"C. Less

C~ 2+ crosses the membrane into the presynaptic (sensory) neuron c. As a result less neurotransmitter is released into the synaptic cleft. This means that an action potential across lhe postsynaptic membrahc is less likely. Fewer action potentials arc produced in the pOSi:syn:lptic m otor neurone so less of a response is observed.

4 Thc snail learns that the stimulus is not c:msing harm, and so it is withdrawing unnecessarily. This effect may be used in its n2tural habi tat when faced with repetitive sti muli, such as vegetation touching the hcild/cye stalks.

5 Rc\e\"ant comments would include: the need for replication using snails of approximately the same siz.e and age; the need to control of t11e size and position of dle stimulation; the need to control other vari:ibles that may ~ifcct the response, e.g. drying Out of the snail; difficulties in determining when i..J-,e snail has fu lly extended (measuring the eye stalk length prior to stimulation may overcome Ll)is problem); effect of handli ng the snail prior to the experiment .

(, lfthe ~nails have been handkd too muc-h prior to tbe experiment, they may h;l\"e alre2dy become habituated to this type: of stimulus so further stimulations will not change the response.

Observing patterns Have you ever walked into a wood and noticed tl1at the vegetation changes as you enter? \\7hy do the bluebells only occur under the trees? O r have you been clamberi ng over a rocky shore and spotted that the seaweeds grow in distinctive bands and that you only find mussels where the tide is far out? What causes these paucrns in plant an~ animal disU"ibution? When ecologists study habitats, they try to :>.ccount for plant and animal distribution, correlating

~~~ _t? tl~e-~~~~-ti~ ~_!ld '[)_i.otic factors . th_at _ar~ affecting the babit~t . . -- . Abiotic means 'non-Jiving' and examples of apiotic fac_t

Completing a transect study One of the easiest pancrns to spot is zonation iii the vegetation and animal distribution- as ycu go from one pl:!cc to another the vegetation and animal distribution changes. A zonation can often be explained by a gradual change (a gradient) in one or more physical or abiotic factors . A transect is often used to study zonation in vegetation or non-mobile animal distribution. A transect is a \inc along which systematic records can be made.

Comparing t\vo sites Frequently ecologists may notice a distinct pattern !hat docs not show a gradual change and may be rdatcd to one or more factors at the two sites. f-or example, the vegetation in one area of a field may be very different from the rest of the f1eld, or the species found upstream and downsticam of an outflow pipe discharging into a river may seem to differ. A transect may not be the best method for this type or investigation; instead sampling of each area may be more appropriate.

Procedure 1 Plan how you are going to collect reliable and valid data that will test your hypothesis. You

need to make the following decisions.

Tl'!e most appropriate sampling method to usc (e.g. random or systematic sampling) . The position and length of any transect to use (Figure 1 ). You need to make sure your transect extc~d: far_e~~::_g_~-1~-~~ -~~~~ -~~~-~~:._~~s~ible zonc:.s.

Thc_~i_ze_ a(l~~m~cr o~.9~~rat_s __ t~ ~~s:~-~2:i!.P2~ The species of Pia~~s and animals you arc to reco;d- you should focus on those \o,.hich wi!.l enable yot: to test the hypothesis under investigation. (You may need to find out more about the species concerned using secondary sources). 'The method to usc fo r measuring abundance.

The abiotic factor(s) you arc going to record. Although you may be investigating the correlation between, for example , soil moisture and the distribution of plant species, there may be other factors that could affect the distribution of organisms. It is not possible to control these variables but you can measure them and take them into account when

2 Collect the"data.

\'(!hen you have collected your data, you must present it in an appropriate way to help you identify any patterns in t.l,e data . For transect data you can draw kite diagrams by hand or use a computer programme such as FieldWorks which may be available from your teacher.

4 Analyse your data to reveal any patterns or significant differences, and explain the main relationships between species and abiotic factors using scientific knowledge. Determine if your original hypothesis was correct. lf you have suitable data, you can calculate correlation coefflcicms between your biotic and abiotic data. For example, you can sec if there is a significant positive or negative correlation between the factor you think is responsible for the pattern and the distribution of the organisms you haYe rec orded . Remember that correlations do not prove cause :tnd effect.

5 In your \VTite~up interpret your results using biological principles and concepts. Su pport any conclusions you make with results. Discuss the limitations of your results and conclusions based upon them, and suggest modifications that you could make to the procedure.

Edncel p;acticol materials cre; red by Saltcrs -Nuffield Adl"anced Rioloi!Y, OUn:,eaity of Y()ck Sci.nce Ed uc:o.ti.on Group.

Why sample in ecology? In an ideal world when investigating, say, the number of dandelions in two mead ows, you would count C\'cry single dandelion in each. The problem is that this might take forever and become very, very boring. So, instead, you need to take a sample. You might estimate the number of dandelions in each meadow by counting lhe number in sever

lf you are sampling fixed objects within an area, for example the area of Pleurococcus (an ~lga) on the shaded side of trees in a wood or the number of woodlice under rocks, you could number all the trees or rocks and then use random numbers to select which trees or rocks to sample.

This sampling idea is also used when measuring the number of cells in a culture. The culture is mixed to give a reasonably uniform distribution of cells and then a known volume is placed on a hacmocytomctcr (a special cavity slide with a ruled grid in the centre). You then count the number of ceUs lhat occur in, say, 25 squares of the grid . Because you know the dimensions of the grid squares and the depth of the liquid above the square, you can work out the volume of culture in each square, and then calculate a mean number of cells per cm3

qfthe culrurc.

Systematic sampling Random sampling may not always be appropriate. If conditions change across a habitat, ior example across a rocky shore or in a sloping meadow that become~ more boggy towaq:!s one side, then systematic sampling along;;;nsc~~ ~U;\~~ the changes t~ ocStiJ(ff~d~-A ~an~e~~

i~_tjye!Y. !:}~!;.~_l~i9 9!:-!t_a_qp_s~ th~_hflhgh usually using a tape measure, alongWhlCh'" samples are taken. The sample points may be at regular intervals, say every 2m across a field, or they may be positioned in relation to some morphological feature, such as on the ridges :and in the hollows in a sand dune system.

Sampling techniques Quadrats

Qu~:ats are _:J_~~~-f.~! ~~-~'?..~-~.!LE~~1-~Q..rn.rnuoities, and ~~l]Lt?I.J.!.~~;L

o s Stu ,eF)'t."' \"-f:' ';"/ "F_f L Jo'l.;t ~Yt}:.jt? ).~,l- .S'', ~ ~ - '

metal sp ;~ e (such as a tent peg) inser ted in ground

Figure 2 A point quadra!/filmt . hch plan t spccies louchtd by the needle is ftcorde d.

Methods of measuring abundance Density Count the number of individuals in several quadrats and take the mean to give nu mber per unit area, for example per metre squared (m- 2) . In many plant species (e .g. gra sses) it is very difficult to distingui sh individual plants, so measuring density is not possible .

Frequency Frequency is the number or percentage of sampling units in which a particular species occurs. This avoids having to count the number of individuals. If dover was recorded in 10 of the 25 squares that make up a 0.25 m2 quadrat frame, the percentage frequency would be 40%. You n~cd to be consistent when determining presence or absence in a sampling unit. For example, you m ight decide that only plants rooted in the square arc counted, or you might decide that any plant or animal in the quadrat is counted indu9ing any that touch or overhang the quad rat.

Percentage cover This is the percentage of the ground covered by a species within the sampling u nit. Count the: number of squa res within the quadrat th3t the plant completely covers, then count those that are onl y partly covered and estimate the total number of full squares that would be: completely covered by that species.

Estimating animal populations Quadrats cannot be used fo r mobile animals as these don't stay in the quadrats. A varie;y of different nets and traps need to be used. Animals that occur on the soil surface may be: sampled using a pitfall trap (Figure 3) . fbosc in vegetation can be sampled using a pootcr directly or indirectly (after being knocked from the vegetation onto a white sheet). Insects and od1er small invertebrates found in leaf Jiuer can be collected using a TullgiCn fu nnel. Mark-release methods can also be used.

PitfaUtrapforsamptingarthropod~

Pooterforcotlettinginsect.s

Sweep net

Thisnetissweptthrough \ow-growing vegetation, collect;nganyanimals inthemeshnet.

fla t stontprevcnts rainfall filling trap

Tullgren funnel for co!leding organi~ms fromthesoilorleaflitter

Alternativelyamuslinbagofsoil surroundedbywatercanbeused to collect living organisms. This lsaBa ermann funnel.

~ 60Wbolb ' soil sample in muslin bag

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Measuring abiotic factors when sampling t he environment

Angle of stope Usc a !!n~_g.:r. Aspect Use a compass.

Temperatu re Use a t~or temperature probe, but be aware that the time of day can influence the values obtained, as will cloud cover. 111c thermometer or probe should be placed in the same position each time a measurement is made to allow valid comparison of measurements.

light Usc a lig~t met_cr. Light readings can vary widely wilh time of day and cloud cover. It is better to take all measurements O\'er a short period or take regular read ings over extended periods using a datalogger.

Oxygen concentration Jn aquatic systems, oxygen probes can be used to measure oxygen conc~ntration .

.?---=--Humidity Relative humidity can be measured using a :vh_!rl i?g hygrometer. It needs to be spun for 60 seconds just above the vegetation before ~~adT;;g~-;;-t~k~n from the wet and dry thermometer and used to determine the humidity from a calibration scale.

Conductivity . The ability of a water sample to carry an electric current gives a measure of the dissolved

mineral salts. The conductivity of pure water is zcroi increasing ion concentration raises the conductivity.

Soil water A sample of soil is dried at 1 tO "C until there is no fu rther loss in mass. The% soil moisture can be calculated using the equation:

%soil moisture = mass o f fr::s::i~ ~e:a:~~f dry soil X 100 Soil organic matter A dry soil sample of known mass is.. heated in a crucible for 15 minutes to burn off all the organic momer. The mass is rc-mcasured after the soil sample has cooled. The% soil organic matter is calculated using the equation:

%organic matter in soil= mass of dr::~~ :r ::s:o~burnr soil X l 00 pH Universal Indicator or a pH meter can be used to test pH after mixing a soil sample with water. If using UPJversal indicator in the field, it is best to usc a proper soil testing kit that contains som e long glass rubes, v ... ith lines cn~ved on the sides, to show levels for adding soil and chemicals. First, 1 cm3 of soil is shaken \\ith distilled water before adding One spatula of barium sulphate (low hatard). This helps to flocculate (settle) the day fraction, which is important as clay pru-ticles are very sma!\ and will othcrvvise cloud the water for days. Then 1 cm-l of pH indicarorsolution is added and the pH recorded after the contents of the rubes have been allowed tO settle. Edex o:~ l pr~cticl material! created by So lter!~ufflcld Ad,onccd Biology, C.Univeuity of York Scimc:e Edoc~r:ion Group.'

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To investigate the effect of temperature on the hatching success of brine shrimps. To develop certain experimental skills. namely considering the ethical issues arising from the use of living organisms, presenting results, producing reliable results, identifying trends in data and drawing valid conclusions.

Brine shrimps Brine shrimps arc small, saltwater crustaceans; the adults arc abQut 8_!Tl...!!}_Ln_k:ng!b.They arc relatively easy to keep in the laboratory and will produce dormant egg cysts that hatch to produce young shrirntJl:i-r~ae . .~ : ~

first

Orawings!oJhow{eaturelo{brine shrimps

Procedure

You will need: Brine shrimp egg cysts Zgseasalt for each treatment 100cm1 de-chlorinated water for each treatment

40 cm3 beaker of salt water 100cm3 beake~s (one fer each temperature to be tested) Water baths or incubators (one for each te mpera ture to be investigated)

Stirring rod Magnifying glass Pair of forceps Fine glass pipette Bright light Access to refrigerator Sheet of A4 white paper Sheet of graph paper 3 em X 4 em

1 Decide on a range of temperatures from 5 oc to 35 octo be tested .

. 2 Place 2g of sea salt into a 100cm3 beaker.

3 Add l00em3 of de-chlorinated water and stir until the salt completely dissolves.

4 Label the beaker with sea sah and the temperature at which it will be incubated .

Place a tiny pinch of egg cysts onto a large sheet of white paper.

Ed~xcel pr~cticl mattriah cr~J!ed by s~htu-Nuffield Adv;nced Dio!o~. CiJni,ersiry of York Sckr.cc Eduaorion G roup.

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6 \Vet the piece of gr

fr

-your teacher very carefully.

Practical PCR Scientists in forc~sics laboratories carry out the polymerase chain reaction (PCR) using a machine c2.!led an au tomate~ ~th~_rma.J.EY..flq. This is a prograrrunable heating unit in which the DNA to be amplified is incubated in a buffer solution with thcrmo~stable DNA polymerase, primers and deoxyribonucleotides. The unit maintains the cydical sequence of temperatures for the PCR proc~~s.

Your school o:- college may be lucky enough to possess a thermal cycler but it is possible to carry out PCR without them, using three separate thermostatically controlled water b:alhs. You simply have to move the DNA sample from bath to bath- and complete 30 cycles! You need a stopwatch, good teamwork and some sort of protection from the steam coming off the honest bath.

Having amplified the short tandem repeat sequences within your DNA sample, you wi!l then separate out the fragments using gel electrophoresis (see Prat:tical6.1). Comparing the position of the bands on t~e gels to a standard or reference you will be able to draw conclusions about the DNA sample you started \\~th.

You will follow a praclical protocol supplied by lhc comp:my lhat produces the equipment and reagents your school or college has purchased .

" \

To investigate the effect of different antibiotics on bacteria.

Introduction

Wear eye protection. The microorganisms are a potential biological hazard. Use aseptic technique s when transferring the bacteria to the Petri dishes. Clean the bench with antibacterial disinfectant. Do NOT open the Petri dishes once th ey have been incubated.

When a bacterial infection is diagnosed it is useful to be able to tell to which antibiotics it is most susccpLib\e. In some cases this information is known, but in other cases tests need to be carried out to find out which antibiotic will be m os t effective. In this activity you will be testing the effectiveness of several types of antibiotics on bacteria .

The standard method of doing this is to put discs of chromatogra phy blotting paper soaked in the various antibiotics OntO an .~~!.r. el~te that has been inoculated with the bacteria. Alternatively a Mast ring (a ring of paper with several 'arms', each treated with a different ant ibiotic) can be used.

Procedure

You will need: Agar plate seeded with a known bacterium Bunsen burner Bench spray of disinf~ctant. 1% Vir~on or equivalent Soap or handwash Paper towels

Marker pen Autodaved forceps !"last ring or antibiotic-impregnated paper discs Adhesive tape Eye protection

1 \\lash your hands wilh the soap or h:mdwash. Spray the working area thoroughly with L'"le di~infectant spray: Lea\'e for at least 10 minutes, then wipe wilh a paper towel.

2 \\'ork \'Cry close to a li t I3unsen burner. Prepare an at;ar pl ate seeded wiih ba ctcr ia.Thi~ m:ly ha-.e already been done for you. If not, follow the insuucrions in the section 'Pouring agar plates' in Practical 4.3 EdexcelAS Biology. Label the Petri dish on the base at the edge \\'iL~ your name, the date and the type of bacterium it is inoculated with .

3 Flllmc the _foret.'l)S and then usc them to pick up an amibi~tic disc or Mast ri ng. Raise the lid of the Petri dish and place the Mast ring firmly in the centre of the agar; if individual discs are used they will need to be spaced evenly around the dish .

4 Tape the dish securely \\ith two pieces of adhesive tape (but do net seal it COf!lplctely), then keep it upside dov.m at room temperature for 48 hours.

Edo~cd pr~ctical rr.O! ~ri31< crnted by Soben.Nufficld Ad,anced !liology, OUnivcrsity of York Science Educ~tion Group.

\X.'ash your hands with soap or hand wash and clean the bench again using the Virkon spray.

6 After incubation, look carefully at the plate but do n ot open it. Where bacteria have grown the plate will look opaque, but where the antibiotics have inhibited growth, clear zones called inhibition zones will be seen. Measure lhe diameter of the inhibition zones in millimctres and use this information to decide which antibiotic is most effective at inhibiting the growth of the bacterium.

7_ Collect data from other ~embers of the class who used lhc other bacterial cultures. ~ 8 \X' rite a brief report of the results, comparing the different nntibiotics and the effects on

the diffcrcm bacterial cultures.

Questions 1 Arc the inhibition zones circular? If not, what is a sensible measuring strategy?

2 What factors .determine the diameter of the inhibition zones?

3 If class data arc shared:

a what is the overall spread of the data

b do all individual results show the same trends- if not, why not, and how could this v;~riability be represented on your graphs?

4 If you were working in a hospitallaborarory, and you had just ca rried out lhis test on bacteria isolated from sick patients, would you always choose the antibiotic that gave the biggest inhibition zone? Arc there any mhcr factors you would need to consider?

respiration. To measure the rate at which an organi;m respires.

Soda lime is corrosive. Do not handle directly: use a spatula .

You will need:

Respirometers Respirometers range from relatively simple piec.::s of equipment used in school science labs with seeds or invertebrates, to elaborate devices the si ze of a room used to measure respiration rates in humaOs living near-normal lives over ::. i)'.!riod of several days . In this practical you will be using a very simple respi rometer, while considering the advantages of some of the slightly more complex ones.

Procedure

Respirometer (see diagram belovo')

Soda lime Coloured liquid Dropping pipette

Solvent (to remove the marker) Cotton wool

S g of an actively respiring orga nism Permanen t OHT marker pen

Stopdock Eye protection

1 Asscmb!C the a:pparatus as shown in the diagram below.

scale

\""1'''\ ''''1"''\''''11''''1 "''1"'''1 ""1" '1'"'

I ltmlpipetteorg!asstube coloured liquid

small organisms

gauu

Aiitnplerespirome!er

i Place 5 g of maggots r>r peas into the test tube and replace the bung.

--- - --------- - - - -----.- ---~

3 Introduce a drop of marker fluid into the pipette or glass tube using a dropping pipeue. Open the connection (three~way tap) to the syringe and move the fluid tot\ convenient place on 1J1c pipette (i.e. towards the end of the scale that is furthest from the test tube) .

4 Mark the starting position of the fluid on the pipcne rube with a pcrm.ancnt OHT pen. 5 Isolate the respirometer by closing the connection to the syr inge and the aunosphcrc and

immediately start the stopclock. Mark thC position of the fluid on the pipette at 1 mi nute intcr\'als for 5 minutes.

6 At the end of 5 minutes open the connection to the: outside air.

7 Measure the distance travelled by the liquid during each minute (the distance from one: m ark to the next on your pipene). 1f your rube does nor have volumes marked onto it you will need to convert the d istance moved into volumt: of oXygen used. (Remember the volume used = # X distance moved, where r = the radius of the hole in the pipenc.)

9 Record your results in a su:tablc taQ.le. 10 Calculate Ll,e mean rate of oxygen uptake during the 5 minutes.

Questions 1 \\ihy did the liquid move? Explain in detail what happens to the oxygen molecules, the

carbon dioxide molecules and the pressure in the tube. 2 It would have been better to set up a second, control tube that did nOl contain living

organi sms but had everything else the same. a W'h:n could cause a movement of the liquid in the control tube tQ\vards the respirometer? b \X'hat could cause a movement of the liquid in the control tubc away from.the

n:spirometer? c \V'hat could yo u do to cor rect your estimate of oxygen uptake if the liquid -in the

control had moved too?

Extension 3 The diagram bdow and Figure 7.24 on p~gc 148 of A2 Biology show two other types of

respirometer. \Xfh at advantages and disadvantages do these have compared to the one you arc using?

sod~

A vtry ~imple respirometer

drop of liquid

I l-=-rapi!\~ry tube

4 Design an experiment to investigate the effect of diffcrenl tempcrarurcs on the rate of oxygen uptake in maggots. Remcmbcr that the maggots will need time to acclimatise to each new temperature .

nnd rate of breathing. Soda lime is corrosive. Do not handle directly: use a spatuh1. A spirometer should only be used with supervision. !f you have breathing or circulation (heart) problems or suffer from epilepsy you should not use the spirometer. Read the manufacturer's instructions and safety notes before_ using the equipment. Stop using the spirometer at once if you experience any unusual breathing problems or feel dizzy or uncomfortable. (Asthmatics may use a spirometer if they are otherv.dse in good health.) A trained member of staff should use an oxygen cylinder to fill the spirometer.

Using a spirometer The apparatus shown below is a spirometer. Spiromctcrs allow us to study both breathing and respiration. In this activity you will !earn how a spirometer works and how to interpret the spirometer trace that is produced.

A spirometer

The general principle behind a spirometer is simp!e.lt is effectively a tan.l

Tubes ru n from the ch

Switch on the recording apparatus and at the end of an exhaled breath rum the tap so that the mouthpiece is connected to the spirometer chamber. The trace will move down ns the person breathes in. After breathing normally the subject should take as deep a brea th ns possible and then exhale as much air as possible before returning to normal breathing.

A sketch c[ a trace sf: owing normal breathing and one forced breath in and out

A diagram of a spirometer trace is shown above. In this example the subject has breathed in and ou: normally three times, then taken as deep a breath in as possible, then forced the air from their lungs. Several pieces of information about the subject's breathing can be read off this kind of uace, oi worked out from it.

The tidal volume is the volume of air breathed in and out in one breath at rest. The tidal volume for most adults is only abo~~.5?;~T.3 Vital capacity is the maximum volume of air th:.:n can be breathed in or out of the lungs in one forced breath .

Breathing rate is the number of breaths taken per minUlc.

Minute ventilation is the volume of air breathed into (and out of) the lungs in one minute. t\1inute ventilation.= tidal volume X rate of brcaL,ing (me;~surect in number of breaths per minute).

Some 2ir (about 1 dm3) always remains in the lungs as residual air and cannot be breathed out. Residual nir prevents the walls of the bronchioles and ahcoli from sticking together. Any air breathed in mixes with this residual air.

Collecting data on rate of respiration Each time we take a breath, some oxygen is absorbed from the air in the lungs into our blood . An equal volume of carbon dioxide is released back into the lungs from the blood.

When we usc the spirometer, each returning breath passes through soda lime, which absorbs the carbon dioxide so, with the canister in place, less gas is breathed back into the spirometer

-- d -~

ch~mbcr tha n was breathed in. If we breathe into and out of the spirometer for (say) 1 minute, a steady fall in l.h l!: spirometer trace can be seen. The gradient of the fall is a measure of the rate of oxygen absorption by the blood, and so is a measure of lhe rate of respiration by the body.

1 Using th e trace produced in class, or one provided by your teacher/lecturer, find the following values:

a tidal volume

b viral capacity

c breai.hing rate d minute ventilation.

Use the u-acc produced in class, or one provided by your teacher/lecturer, to work out the rate of oxygen consumption in someone at rest.

3 What differences would you expect if the subject had been exercising before a tra ce was taken?

4 Describe how you could use the apparatus tO measure changes in breathing and respiration rates due to exercise. (Note that the apparatus you have used may not be suitable for use during exercise, and that measurements need lObe taken immediately af1er exercise has stoppc9 . Discuss \\ith your teacher which is the best method for usc with your apparatus.) State what exercise would be appropri:ne, and any hazards involved. Sketch the shape of the u-ace you would expect bcfor~ and after exercise.

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Touching snails Lots of people:, at some time in their childhood, will have touched a snail in Lhc garden and noticed that it withdraws its eye stalk-s into its body. For such a slow-moving animal !his seems a very quick response, this suggests it is an important response for protection and survival. A snail o~y withdraws into its shell when it is either inactive or threatened. When touched, it withdraws to avoid danger. Do snails b:come habituated to the stimulus, ceasing tCl withdraw ""-'ilh repeated stimulation? In this imestigation you will collect data to find o~t if habiruation to a touch stimulus does occur in these organisms.

ready fo r disinfection. Take care that the stimulus causes no harm to tha snails.

Procedure

You will need: One giant African land snail (or a garden snail if not available} One dampened cotton wool bud Suitable dean, firm surface for the snails (e.g. a plastic chopping board} Stopwatch

1 Collect one giant African land snail, and place it on a clean, firm surface. Allow the snail . to get used to its new surroundings fOr a few minutes until it has fully emerged from its shell.

Dampen a cotton wool bud with water.

3 Firmly touch the snail between the eye stalks with the dampened cotton wool bud and immediately start the stopwatch. Measure the length of time between the touch and the snail being fully emerged from its shell once again, with its eye stalks fully extended.

4 Repeat the procedure in sti=:p 3 for a total of 10 touches , timing how long the snail takes to n:emergc each time.

5 Record your results in a suirable table.

Present your results in an appropriate graph .

d~J':lnt ed Biolor., OUniversity ;)(York Sciemce E.:luc:~tion Group.

-- -~----- ----~-- ------------ -------~--------------- -

~ :::s

Questions l Write a hypothesis which this experiment will test.

2 Using your graph, state if you think there is a positive, negative, or no, Correlation between the number of stimulations and the time for eye stalk withd rawal.

3 Explain any patterns or trends in your data, supporting your ideas with evidence from the data and your biological knowledge of habituation. Relate your findings to your . hypothesis.

4 Suggest a reason why snails may become habituated to a prodding stimulus in the wild.

Evaluate the procedure used for this experiment.

6 1l1is experiment has been shown to be Jess successful if the snails arc handled regularly prior to the experiment. Suggest why handling prior to the experiment could affect the results of the experiment.

Going further 7 Writt": a null hypothesis that this experiment will test.

8 Complete a Spearman's rank rl correlation test to determine if there is a statistically significant correlation between L~e variables. A table with the headings below will ht':lp.

Number of time:; Rank :;timulation Timef:;econd:; Rank time Difference/D D2 the snail has been stimulated

9 Usc a t

1 The diagram below shows an outline of the light-independent stage of photosynthesis, together with some of the products.

A ~~)

l pho5phory\~ted 6C 5ugar

' \ gluco~~

note GALPis glyccraldchyde 3-phosphatc.

a Using the information provided in the diagram, identify substances X andY and state the number of carbon atoms prc::;ent in each. X ~- '. // y ":"! -)

b Explain how substanceY is converted to GALP. ~,. ' \ \L;r : ~

J

c GALP is converted to a phosphorylated 6-carbon sugar which in turn ca n be con\'erted to a number of prod~cts such as sucrose and glucose. Sucrose is translocated around the plant in phloem.

Describe how phloem tissue is adapted for this function.

(2)

(2)

(6)

{Total10 marks)

....... ____ tlllll

2 A study of plant species ncar a S~.!.!_~~

3 Pollen grains buried iu peat can be used to deduce what Lhe climate was like in the past.

a (i) St?.tc how the age of a peat layer can be estimated. (1) n .

(ii) The presence of a large amount of alder tree pollen in a layer of peat is taken to mc:m !.hat there was high rainfall when ihe layer was formed . Suggest why it is thought that the presence of alder pollen in peat indiccnes hi gh rainf;>il. {_1)

b The cxdske\etons of many ins~:ct species are also found in peat. Exoskeletons arc resistant to decay. Suggest how insect exoskeletons from peat could be used to show that the climate became warmer over a period of years.

Ar~t ic O cean

(2)

c Certain arctic plams are adapted to growing in very cold conditions in the treeless tulidra habitat of northern Norway, Sweden, Finland and Russia, ncar the coast of the Arctic Ocean.

(i) Suggest why the geographical location of arctic plants makes them especi:>lly vulnerable to extinction due to global w~mnlng. (1)

Edexccl A2 iJj(>logy ltnpl~mcnlation ~nd Allc>n C r uuon Educ:olion Limi1cd 2009

- ------------------- ----- - - - --- ------ ------------ __________ -.;

(ii) Increase in temperature increases the rate of respiration more than it increases the rate of photosynthesis. Suggest why this might be a problem for arctic plants affected by global warming. (2)

~ .....

(Total 7 marks)

4 An investigation was carried out into the mating preferences of cichlid fish from three populations (A, B and C) taken from Lake Malawi. The fish were all the same specit:s, bur the males o f each population showed distinct physical differences.

Male fish were separated into different areas of a tank by transparent plastic sheets. The plastic sheets had holes \vhich allowed any female to enter, but p revented the males from leaving.

The diagram bdow shows the arrangement of the tank.

lr~n1pM~rlt pl~s:ic sheets

I~ """oole big ooocgh """' for fem~\~ to gl;,ss tank

pas~ through

Females fr01n each population were allowed to choose one mate, and their offspring were eollcctccl. The male parent oi the ofispring was determined using DNA analysis.

Ed~>;cd A1. Diolog:y !mplemcmoon and Aw:ssmcn\ Guide forT~ac~.ers 'ndTech:"liciam OP~;rw:. Edueaticm Li.miled 2009

~---------

The tabl e below sh ows the number of times mating occu rred bc.tween i J;ldiyiduals of the different populations in a range 9f ~ia\s . ---------- ~ .. -

Female from population

Mal~ from populat ion A

29

26

a Explain how the DNA analysis provides reliable cvide"ncc fo r the identi ty of male parents.

b (i) Calc\1late the perccntagt of the matings that were between individual s of the same population. Show your working.

(ii) Describe the mating preferences shown by the female fish in this investigation.

c Suggest how the data support the hypothesis that population A is the most likely to become a separate species.

(3)

{2)

{2)

(4)

(Tota\11 ma rks) {TOTAL for test 38 marks]

Edexcd A2 Biolor.~lmp!emen totion and As1essmen ~ Guid~ for Te ~ che rs a:~ d Technici 3nS CPe3rWn EdllC~tion Lim ited 2009

1 The diagram opposite represents the structure of a uam;fcr RNA (tRN/\) mo\ccuic. Transfer RNA has a simil ar structtJrc to messenger RNA (mR . .L'J"A), but the single suar::d of nucl cotides is folded back on itself. The. folds arc held in place by base pairing.

a List the four bases in tt,e regior.labellcd A which pair with those already shown. {1)

b The three !:haded basr:s in ngion B arc responsible for bind ing to an m RNA molecule durir:.g translation. Give the n:;me used to describe LI-tis group of three bases on the tRNA.

c Each amino acid is coded for by three bases on the mRNA molecule. Explain why a group of three bases is the smallest number that can be used to code for ail of the amino acids found in proteins.

d The particular amino acid bound to a tRNA molecule depends on the three bases at position 13. Explain why thls is important during the translation of mRNA to

(1)

(3)

form a polypeptide. (2)

Edexcd A2. Biotcor;y lnpkrn~n:.otion o.nd Aucummt Guic!t f.:>< Teachers and Tccl~"lici~n OI'olt>Ofl f:duc~tio" Limited 2.009

----... - ..

e In an eXperiment to investigate the role of tRNA in the synthesis of proteins, cells were exposed for a brief time to radioactively labelled amino acids. Samples of the cells were then removed at intervals over a period of 20 minutes, and the level of radioactivity associated with tR_~A and protein was measured as counts p

2 r\ person suspected of being exposed to the Human lmmunodeficicncy Virus (HlV) may have their blood tested to check for infection. Same tests determine whether antibodies that act against lhc virus_ proteins arc present in the bloo~ . a Explain how the presence of HIV proteins in the body results in the production

of specific antibodies.

b The graph below shows the change in t.~e numbers ofT helper cells in a person infected with HIV.

l =!~~ili~~~i~~~;~~j I \ilt~~t!!~~~

0 . ' . " ' ' 1 ,

Timesinteinlection/yearl

(4)

T helper cells arc needed for z\1 immune responses. Fe\vcr than 200 cells per mm3

prevents an dfectivc immune response. Usc the information in the graph to describe how HIV infection is likely to affect this individual's health. {4)

{To tat 8 marks)

3 The graphs below show changes in the.nuantities of an antibiotic used in a hospiral and the percentage of infections caused by b3ct~ria resistant to the antibiotic over the same time period.

12

87 88 89 90 91 9Z 93 94 Y?ar

a Using the information in the graph , ~::xpiain how bacteria become res;),lant to antibiotics . Use the information in t11c graphs to sup pon your answer. (6)

b Bacteria were grown on an agar plate and incubated with four different antibiotics 1l1c antibiotics were placed on paper discs. The resulting plate is ~hown in the diagram below.

arrawtth no

Edcxcd Al Biologylmpl:m~mnio~ a:-.d A1scssmcm Guide forTe ochen ~~dTc h.~;cia

(i) GiYe one piece of evidence that susgcsts that antibiotic B is more effective at killing th~sc bacteri

a (i) Give one factor) o!.her than temperarurc, that could affect the growth of insect larvae on a dead body. (1)

(ii) Sugges~ and explain reasons why the time since dcmh thn larvae first appear on a body is different for each species. (4)

b The growth of !.he l:;.pae is affo!ctcd by tcmp..:rl!ture as shown in Table 1. T he effects of temperature are given as Lhe number of days ahead (+)or behind(-) their development at 22 C.

Effect on development/days

Temperature/C Housefly I Flesh fly 12 - 4 I - 4 27 +! I + 1.5

Two d ead bodies were found at the same address and evidence was needed to decide whether they died at the same time. One was found in a boiler room with a temperature of 27 oc and the other was found in an outside shed where the te mperature was 12 oc.

Insect larvae from both bodies .were collected) identified and measured . The results arc shown in Table 2. T;lble 2

Mean length of larvae/mm

Site of body House fly I Flesh fly Boiler room 23 I 45 Shed I 23

(i) Usc the information in the graph, Table 1 and Table 2 for flesh fly larvae to estimate the time of death for the body in the boiler room. The estimate using house fty larvae has been done for you.

length/mm

House fly 23

Flesh fly

Suggested time since death at

22 C/days

Adjustment fo

ZPC/days

Estimated actual time since death

/days

(2)

Edc 'nd Technici~nl OPC11rs.cn Edueuion Llmitcd 2009

__ ,..

(ii) Use tl1e measurements of larvae from the body in the shed to provide evidence that the two deaths occurred at approximately the same time. (3)

(Tota l 10marks) [TOTAL for test 41 marks}

Edcxcd A2 Riulog)' lmpkmen:nion and Assessmtm G..:de forTcacbc~ andTcchr.ici~n~ OPt:u~n Eduatin L.im.itcd 2009

0

'0

'

1 The diagram below shows part of a myofibril in a relaxed muscle.

~.A~~ B ; ~

-a Name the pans labelled A and B. (2)

A -------------------------------------------

B -------------------------------------------b In the space below, make a drawing to show this part of the myofibril when it is

ful ly contracted . (3)

c D escribe the role of calcium ions in muscle contraction. (Z)

[Total7marks]

2 Diagram A and diagram B below show recordings of the breathing patterns of a person. ln diagram A the person is at rest. In diagram B the person has just finished a period of strenuou s exercise .

Di ~g ramA:at r~st

~.l\t.':;:;:j -;-1- "-:1 iH- i-"'-1

~1~Ho '

,o

"

Time /~

Edexccmtm Cu:dc forT;,achcrs ~ nd T

Time/~

a Ct~lculatc the mean tidal volume between 10 and 30 seconds when the person is at rest. Show your working.

Answer - - - - -- (2) b The ventilation rate of a person can be calculated by multiplying the rate of

breathing by the depth of breathing. Usc diagram B to calculate the ventilation rate of the person during the first I 0 seconds after exercise. Show your working.

Answer _____ _ (2)

c Using the data in the recordings, compare the breathing patterns of this person before ::md after exercise. (3)

This person then un dertook a physical training programme.

(i) Describe and explain two differences lhat you would expect to sec in the breathing patterns of this person following exercise as a result of the training programme. (4)

(ii) Suggest how the uaining programme might affect the cardiac output of the person . (2)

[Total 13 marks]

During investigations into the control of body temperature, the internal (core) body temperantre of rr th in human volu nteer was recorded at intervals .

In the fi rst investigation, the volunteer sat still for 30 minutes. H e then got into water at 16 cc, where he_ lay still fo r a further 30 minutes. In the second investigation, the body temperature of the same volunteer was recorded at imerva\s for 30 minutes while he was sitting still . He then went swimmi ng in \Vater at 16 '"C for 30 minutes and his body temperature was again recorded while h e was swimming, and irTI.mcdialcly after he stopped .

The results arc shown in the table below.

nme/mi nut es First investigation

Body temperatu re/"C Second invest igation Body ternpcraturerc

373 37A ~----~,~,------~-----~,~,~ . ------+-----~,~,_~, -------30 37.5 [got into water] 36.9[startedswimming]

f--------- --''"-0 - -----+--''-'-'c'. "'[ly-'-io,_g i"-' -~~~-36.0 [swimm~nz] f------__:5~0 ------+--3_7._1 "{ly_in,_g _in_wa_

a State where in the body the tcmpcraturc~rcgulating cen tre is situated .

b Explain why the volunteer's body temperature decreased when he was lying in water at 16 C.

~ c (i) Compare the changes in body temperature when the volumeer was lying in water with the changes when he was swimming .

(ii) Suggest an explanation for the difference in the change in body temperature when. LI-te person was swimming, compared to lying still in water.

(1)

(2)

{3)

{2)

[TotalS ma rks]

4 Isolated mitochondria in a solution contai ning inorganic phosphate and an electron donor ca:1 be used to study rcspiration .. An electrode is used to record changes in oxygen concen tration v.hile mi tochondria respirc. 111c graph below shows changes in oxygen concentration for some isolated mi tochondria.

a (i) Describe and explain the trends shown on the graph above. (3)

(3)

(ii) Name an electron donor used in the electron transport chain in mitochondria. (1)

(ii i) Scate the location of the electron transport chain in mitochondria. {1)

(iv) Describe how ATP is synthesised in the electron transport chain. (3)

b ATP is used to provide an immediate supply of energy for biological processes. Describe the role of ATP in the following processes.

(i) Nerve impulse transmission

(ii) 1-Iypcrpolarisation of rod cells in the retina

(2)

(2)

[Tota\12 marks} [Total fo r test 40 marks]

Ednce! A2 Biology !mplemcotltio" a"d Au~tion Limited 2009

HJIIIB

1 The diagram below shows a section through a human brain .

Complete the table bdow by \vri ting in the letter and the name of the region of the brai n that carries ou t each function.

Func.tion

Init iat ing and controlling voluntary muscle

Coordinating skeletal muscle movement, balance and posture

Letter Name of region

Controlling heart and

breathi~og~"~"~-----~----------~------------~ [Total4 marks]

2 N euroncs uansm it electrical i:npulscs along their cell surface membranes when stimulated to do so. ~f1>es e im pulses arc called action potcnti:1ls and involn changes i :1 the electrical potential across the membranes du e to movement of posil.i\c ions.

- -------

The diagram opposite shows the distribution of charge inside and outside an unmydinatcd ax on as an impulse p asses along.

Directionofi.""'"

b The diagram below shows two action potentials recorded using an oscilloscope.

+ ...;.- , , -l-1 .J_ ..: &. -20

~

i "

:. !- ;

: 1;11" ~ - 60 -t y ..!. -

-1 H+ t-'

- I+' - ,-

.;_ ..w_ . +1

f- U-l-

- so - H+;. ~ !++r\~~,~- !:~~p~ ~ -100

0 Timefms

-;-f- - --! t,+ ' :j:;-1:1=

+.J.

y}t:tt. T ::

(i) Explain how lhe change in membrane potential bcrween 0.5 and 2.0 milliseconds is brought about.

10

(ii) Calculate lhc number of action potentials occurring per second. Show your working.

Answer ______ per second

(4)

(2)

Ede~c~l A2 Biology Jmp!~menmion and Auessmcn: G\lidc forTeachers and T~hr~cians CIPcat!.On EC~tion Li.'Tii!ed 2009

c Explain what is taking place during the period marhrl X cc :!:e ~-ram in

-~ m

{Total11 n:.:rtks]

3 Research on visual development in cats has led to k."lov.~o:!ge O:how :.......:ormation is processed in the visual cortex of the b rain. The; diagn.:ns bdow shoo.~.' :,he; grov.'th of ncurones in part of the visual cortex after norma1-isu2! de\~..a:t ar.d wh::n the left eye has been deprived of sensory information.

a Use the diagrams above to describe difference\ in t.'le '-ist.:.a! ctt~..CX after sensory deprivation . (2)

b Explain how this type of experiment has p ro,;ded eo.~e::xe which shows the need for exposure to sensory information in normal visual dr\~:;-~:.. (2)

c Describe one other piece of evidence which suggests ti:at !":t::r;:!ns mus t be exposed to pznicular s1.imuli if they are to develop normal ""ision. (1)

jTotal S marks]

4 Sea slugs arc marine invertebrates with gills for gas exchange on their body surface. A sea slug is able to w ithdraw its gill when touched. In ar. investigation into this response, the gill was touched and the time taken for the gill to be exposed again after withdrawal was measured. T11is was repeated at half~minute intervals. The table below shows the results of this investigation

Touch Time t~ken for gill to be exposed again/seconds

First 23.0

Second 9.0

Third 16.0

fourth 4.5 --

~\fth 7.5

Sixth 6.5

Se\enth 6.0

Eighth 4.5

Ninth 5.5

Tenth 6.5

a Describe d1c effect of repeated touching on the time taken for the gill to be exposed again.

b Name the r:pe of learning shown. by a sea slug in this investigation.

~ c Explain how this learned response may be of be~efit to the sea slug in its natural environment.

(3)

(1)

(4)

[Total 8 ma rks]

Ed~nl t\2 Biol o~ lmpkmtmation a"d Assenment Guide forTechcn n'ld Ttc!U"Iiciar.s ~Pea non Education Limited 2009

~ 5 T he hut~an brain has many different ncurQlransmittcrs which influence behaviour. One of these ncurotransmincrs is serotonin. A lack of serotonin in the brain can cause de pression and an excess can cause

c Using the information given1 suggest and explain two ways antidcpressants work. {2}

~ d The drug known as ecstasy (MDiv\.A} can cause ar1xiety.111e diagram below represents an ecstasy molccll lc. Using you r knowledge and the diagrams provided suggest hm>, ecs tasy may have this effect.

0 (3)

[Total12 marks} (Total fo r test 40 marks}

Edexcd I'll IllotoJ.'Y lmpkme'lmion and A~sess:n:n: G~,:ide fo rTe~chers and Trchnb~ns CPe3HO!I F.d"JC2tion Li:nit:

Note; the number of lines for studcms to \nitc their answer is not always a true reflection of the space p rovided on the rc

3 a (i) 1 the deeper the bycr the older (!he layer) I cq; 2 use of (radio) carbon d:ning of !he peat;

(ii) alder u-cc:; grow well in wet places I cq;

1 identify the insects; 2 estimate insect numbers of each species in each layer;

find out which species of insect live in warm place~ (today); 4 reference to incrc

Note; the numbe r of lines for smdems to write the ir answer is not always a true reflection of the space provided on the real examination p~.pcrs or the maximum number of marks that ffiay be awarded.You may wish to provide smdcms with additional paper to complete their answers.

1 a CCUU; b anticodon; c 1 about 20 amino 2cids;

2 (triplet) gives 64 pcrmut:llions J 43; 3 of4 bases; 4 (lowes.: number of bases wit.YJ) enough permutat ions .I calcu lation

shown I one or two bases not ctwugh permutations /. more codes thac needed; 5 code is degenerate I some amino acids have more than one code;

d 1 ensure lhat the correct em ina acid (added to pol_ypcptidc) I converse; 2 fo r given {anticodon I codon (o n mRNA)} I cq; 3 reference to correct st'qm.:m:c of amino :1cids I co rn::ct pol ypeptide s tructure;

(1) (1)

(3)

4 reference to complementary base paiting; (2) c (i) 1 radioactivity in protein rises sharply I cq ;

th en faUs (more) slowly; 3 protein peaks between 5 and 7 minutes;

radioactivity in tRNA fal!s throughout; Compare rate bdorc and after about 5 minutes;

6 reference to a relationship be tween protein and tRNA; (ii) amino acids (had been) taken up (first) by tH.N A;

(3)

tRNA {delivered I released.} amino

3 a /l1l explamHi1n1 to i11cbtJe six from: increased usc;

more bacteria exposed;

reference to mutation;

reference to p\asmids;

reference to conjugation I sexual reproduction; reference to genetic variation I existence of d iffe rent genes; reference to selection by the antibiotic;

descripti on of selection;

refe rence to resistance gene p::1ssed lO offspring;

10 selected o rganisms become more common;

11/12 reference to graphs;

b (i) grcatrr clear area; lii) A11 expl.ana!ioll 10 i11cludc IWO from:

1 htrger molecules I

Note; the number of lines for students to write their answer is not always a true reflection of the space provided on the real examination papers or the maximum number of marks that may be awarded. You mc~increases ; rate of b reathing increases; greater vari

reference to in creased ventilation; (therefore) increases hcat lo!:>s from body; credit reference to the fact that L!-Jc volumec~ was thin therefore less insulating effect of fa t; idea that wum(cd) water is moved 3"-Y from body's surface and temperature gradient maintained ; (2)

[Tota lS marks]

4 a (i) 1 reference to oxygen (concentration) deC::e.as~;g ~ greater (decrease) when ADP is added; (o;t..ygen used to) convert ADP tO ATP (in respiration);

4 oxygen is needed for respiration I eq; 5 correct reference to oxidative phospho:ylaCo=t; 6 reference to {AD P concentration I eq} is limitin&;

(ii) reduced NAD I NADH I NADH2; (iii) eri::i!ac I inner m.:mbranc I stalked particle; (iv) 1 hydrogen

Note; the nnmbcr oflines for students to \\Titc their answer is not always a tnJc rcfieclion of the space prov:dcd on lJ)e re:a\ examination pupcrs or \.he maximum number of mall~s !.bar may be awarded. You may \\ish to pro\id

4 a Att\ll"d Clltl! mark/or ooch ofth.:follu-.JJinj! poims i11 o.mlcxt Loa ma~imum of thr