6bi06 exemplars

GCE

Biology

Support booklet for Unit 6 — 6BI06

November 2008

Tutor support materials

Edexcel, a Pearson company, is the UK’s largest awarding body, offering academic and vocational qualifications and testing to more than 25,000 schools, colleges, employers and other places of learning in the UK and in over 100 countries worldwide. Qualifications include GCSE, AS and A Level, NVQ and our BTEC suite of vocational qualifications from entry level to BTEC Higher National Diplomas, recognised by employers and higher education institutions worldwide.

We deliver 9.4 million exam scripts each year, with more than 90% of exam papers marked onscreen annually. As part of Pearson, Edexcel continues to invest in cutting-edge technology that has revolutionised the examinations and assessment system. This includes the ability to provide detailed performance data to teachers and students which helps to raise attainment.

This booklet must be read in conjunction with the Edexcel Advanced Subsidary GCE in Biology (8BI01), Edexcel Advanced GCE in Biology (9BI01) — Issue 3. Publication code UA018858

Acknowledgements

This support booklet has been produced by Edexcel on the basis of consultation with teachers, examiners, consultants and other interested parties. Edexcel would like to thank all those who contributed their time and expertise to the specification’s development.

References to third-party material made in this specification are made in good faith. Edexcel does not endorse, approve or accept responsibility for the content of materials, which may be subject to change, or any opinions expressed therein. (Material may include textbooks, journals, magazines and other publications and websites.)

Authorised by Roger Beard Prepared by John Crew

All the material in this publication is copyright © Edexcel Limited 2008

Contents

Unit 6 — 6BI06

Introduction 1

Part 1: Practical biology and investigation skills 4

Research and rationale 6

Planning 16

Observing and recording 27

Interpreting and evaluation 33

Communicating 48

Offering students individual opportunities to meet all the criteria 61

Giving help and assistance 64

Appendix 1: Some ideas for investigation 67

Appendix 2: Unit 6 Individual Investigation — Checklist 71

Appendix 3: Guidance for centres on electronic submission of candidates’ assessed work 73

Tutor support materials — Edexcel GCE in Biology — Support booklet for Unit 6 (6BI06) — Issue 1 — November 2008 © Edexcel Limited 2008

1

Introduction

The assessment of this investigation forms the whole of Unit 6. It can be awarded a maximum of 45 marks, which represents 20% of the total A2 marks and 10% of the total GCE marks.

Students submit a written report of an experimental investigation, which they have devised and carried out. Edexcel offers centres a choice. Either:

(a) teachers, within the centre, mark the work of the student and Edexcel appoint an External Moderator to moderate the teachers’ marks

or

(b) the student’s work can be submitted to be marked by an External Examiner appointed by Edexcel.

a. Basic principles

Biology offers unique opportunities to investigate a whole range of interesting questions. Many of these questions have direct relevance to students and can be investigated without the need for expensive equipment. Investigating such diverse and interesting questions can be a highly motivating and hence successful experience for students in contrast to those simply following instructions or attempting to ‘prove’ well-documented ‘facts’.

How Science Works is a key element of all GCE courses. Unit 6 assessment addresses many of these criteria but especially HSW 2, 3, 4, 5, 6, 7 and 8, which can found in Section B of the GCE Biology specification. These criteria are published on page 13 of the GCE Biology specification.

A full mapping of the relationship between these criteria and the learning outcomes can be found in Appendix 3 of the GCE Biology specification.

It would be helpful for centres to bear in mind the following when planning for Unit 6 investigations.

• Given that 20 per cent of the marks available in A2 are awarded for this investigation it would be logical that the time allocated within schemes of work reflects this.

• Whilst the timing of the implementation of the investigation will be governed by the circumstances and preferences of each centre, it is important to consider how students will develop the skills required for the investigation throughout their AS and A2 courses.

• Investigations may be chosen from an extremely wide range of possibilities, either in the laboratory or in the field. However, it is important that all centres ensure that they offer all students the opportunity to devise and carry out their own individual investigation.

• The assessment of investigations is carried out on students’ written reports and hence it is important that these provide clear evidence of the student’s individual ability to meet the criteria.

All reports are expected to be word processed and submitted electronically see Guidance for centres on electronic submission of students’ work, available on the Edexcel website and a copy of which can be found in Appendix 3 of this document.


2

There has been considerable discussion on the demands that GCE internal assessment makes on individual students. In order to help students it is expected that investigation reports will be between 2700 and 3300 words, including abstract, trial, tables/captions, appendices and any other text, but excluding the bibliography. Experience has shown that even high-scoring reports are often far too long with the inclusion of irrelevant material, repetition and over-elaboration. Most would achieve similar marks at much shorter length and therefore it is in the interests of students to keep to this word limit and show clearly the word count page by page.

b. The role of core practicals in preparing students for Unit 6

Unlike in the GCE AS Edexcel (8040) specification students do not have to submit an investigation for assessment in Unit 3. Whilst some skills acquired in compiling the visit or issue report are certainly relevant here, centres will need to consider how they provide opportunities for students to develop the relevant skills throughout the whole course to enable them to approach this investigation with confidence. These skills are central to the incorporation of ‘How Science Works’ criteria into the whole course and will also be assessed in unit tests. Knowledge and understanding of core practicals will be assessed in the unit tests.

The development of many of these skills can also be linked to a structured approach to core practicals and there are some suggestions as to how this might be achieved in the Unit 3 coursework guide. Some further suggestions for A2 core practicals are given here.

Unit 4

5.11 Describe how to carry out a study on the ecology of a habitat

Obviously the scope to use this practical activity to provide specific training in many of the main criteria is very wide. This is regardless of whether it is the intention to use ecological studies as the main coursework investigation. In addition to familiarising themselves with the main techniques students might produce mini plans for investigating interesting questions around the school grounds.

For example:

• Does the abundance of one species of plantain (or other species) vary with the amount of trampling on a sports field ?

• Does the pattern of vegetation change as you move away from a large hedge?

• It is usually possible to completely clear a small area of ground each year so that simple patterns of succession can be investigated.

• If trees are present then many will have a green algal coating of Pleurococcus sp. which provide useful investigations.

5.17 Describe how to investigate the effects of temperature on the development of organisms.

Seedling growth rate or hatching of brine shrimps are suggested options for this investigation but this does not mean they are the only options.

Given the simple requirements this might provide an ideal opportunity for students to plan a suitable investigation and to evaluate their ideas following a trial in the lesson. There are excellent possibilities here to consider what exactly might be measured, how might this be converted into a rate and is it a valid measure of ‘growth’?


3

Alternatively this might be approached as a whole class investigation with everyone using a similar technique. If results were collated on a single spreadsheet, students would have the opportunity to select their own methods of presentation and analysis perhaps discussing the pros and cons of different approaches with their peers.

Unit 5

7.6 Describe how to investigate rate of respiration practically.

Simple respirometers consisting of a boiling tube, wire shelf for a carbon dioxide absorber and a rubber bung fitted with a length of capillary tube can provide many opportunities to understand the principles of respirometry and the problems of controlling variables such as temperature. It is unlikely, even with more sophisticated apparatus, that students will be able to produce sufficient data for analysis in the time normally allocated to this practical. However it does provide an excellent opportunity to discuss experimental limitations in depth and could be used to consider important aspects of rate measurements if supported by some second hand data for analysis.

7.14 Investigate the effects of exercise on tidal volume and breathing rate using spirometer traces.

Obviously only a limited number of centres will have a spirometer but much cheaper ‘chest-expander’ type sensors are now available for use with data-logging equipment which can give useful traces.

Even where secondary data is used to show traces it is important to ensure that there is some form of time scale indicated on the horizontal axis in order to assess rate.

Once again the opportunity exists to discuss in depth the problems of controlling such things as human samples and exercise intensity. Similarly the voluntary control of breathing also causes difficulties.

8.15 Investigate habituation to a stimulus

There are several alternatives to this investigation. Using snails’ antennae might be the simplest (Giant African Land Snails are particularly useful).

In addition to other skills the use of ingenuity in design might be encouraged here by attempting to brainstorm ideas on how to apply a constant stimulus — a particularly important piece of planning for habituation studies.


4

Part 1: Practical biology and investigation skills

Assessing Individual Investigations

Investigations may be assessed by centres internally and subjected to external moderation or they may be submitted to Edexcel for external marking. In either case some common principles will apply.

a. Applying the criteria

The criteria are to be applied in a strictly hierarchical fashion. ALL the criteria which are applicable to any mark range must be met before a higher mark can be considered. For this reason it is important that students check carefully that they have attempted to address all the skills described. For example, a student who fails to carry out a trial experiment for section (a) of planning cannot be awarded more than 2 marks for planning, no matter what standard has been achieved in Sections (b) and (c) of planning.

The nature of the criteria means that in all sections there are quality judgements to be made. Past experience has shown that, where significant differences arise between examiner or moderator and centre marks, it is common to find very high level mark ranges awarded where there is only very brief mention of the relevant points.

Whilst the criteria must always be applied in a detailed manner it is helpful to consider the mark ranges as a whole to check the final mark awarded is fair. Where there are three ranges then these might be regarded as follows in relation to what might be expected from a typical A Level student.

0–2 (0–3) = Weak

3–4 (4–6) = Average > Good

5–6 (7–9) = Very Good

Where there are four ranges then the middle ranges could be regarded as ‘Average’ and ‘Good’ separately.

It is helpful to use this type of category during internal standardisation to ensure that the order of merit for different pieces of work is verified.

When annotating work the following abbreviations should be used to indicate sections in the report, which meet the criteria concerned.

Research and rationale = R Planning = P

Observing and recording = O Interpreting and evaluation = I Communicating = C At the end of each section there should be a clear summary list of each criterion covered and how the overall mark for it has been derived.

eg P(a)5 P(b)8 P(c)6 P=6


5

b. Award of intermediate marks.

• Always assess each section (a)(b)(c) of the criteria first.

• Look carefully at each mark. What is the lowest mark range indicated? Where in this range ought the total mark lie? Is there one section which is very weak where you had difficulty awarding that level? If so then the total should be at the lower end of this range. Are all sections strong and is there evidence from some sectors for a higher range? If so then the total mark should be the top of the scale.

• In cases where it is difficult to decide on a mark range it may be sensible, in the first instance, to give the benefit of the doubt to the student. However if you meet this dilemma a second time it would be sensible not to award the higher mark. In this way the final total is more likely to be a fair reflection of the quality of the work. If generous borderline decisions are made repeatedly the final mark often becomes inflated.

Please note that all exemplar student work contained in the remainder of this document has been highlighted with a grey background.

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10–1

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8

Notes on research and rationale

This is an area where students often include too much irrelevant material. Examiners/moderators will be looking for a clear link between the proposed hypothesis and the biological knowledge and understanding described. This needs to be made very clear by the report rather than relying on the reader to interpret a large amount of information. It is hoped that students will draw on skills developed in GCE AS — Unit 3 in this investigation.

Sources of information must be clearly listed in a manner, which would enable the reader to access them if required, and there must be a clear indication of where in the text such sources have been used. The simplest way is to place numbers in the text linking them to a list at the end of the report but other methods such as placing references in footers or adding abbreviations in context, which refer to a detailed list would meet this requirement. Illustrations can often enhance attempts to provide a clear rationale but again these must be relevant. A simple way of ensuring this is the case might be to include only illustrations which had clear labels (fig.1 etc) and which were actually referred to in the report.

There is good practice in many centres that have clear policies on including downloaded material in any form of coursework. Students should be aware that simply pasting large sections of downloaded material together without acknowledgement is not acceptable. (See Edexcel Information Manual — Malpractice available online also the Unit 3 support booklet P76.)

Even where work is to be externally marked teachers signing record cards or authentication certificates are confirming that they have checked the report carefully and to the best of their knowledge, it is the work of the student and any assistance given has been annotated for the examiner or moderator — see further notes on Giving help and assistances (see page 64).


9

The following section contains extracts from three individual investigations:

1. The effect of position on the rocky shore on the number of grey top shells

2. Investigating the effect of ageing on bromelain activity in pineapple

3. Investigating contrast sensitivity in humans.

For each of the extracts the students work has been highlighted with a grey background and commentary has been provided to relate to the assessment criteria.

Research and rationale

Exemplar 1

The effect of position on the rocky shore on the number of grey top shells Abstract: This experiment was designed to explore the effect distance from the sea wall has on the numbers of grey top shells found in a rocky shore ecological system. A series of line transects were carried out to collect information on the number of top shells. Data regarding other variables potentially influencing the abundance of top shells were recorded. This data included temperature recordings at each quadrat, light intensity, the type and number of other species in the quadrat and percentage water cover. Spearman’s rank correlation was used to test the strength of the relationship between two variables, distance from sea wall and number of organisms found. Strong positive correlation was calculated in most transects indicating that as distance increases the number of top shells also increases. Research and Rationale: Grey top shells (Latin name Gibbula Cineraria) are a species of top shell within the mollusc family. They may be characterised by their roughly triangular shape and distinctive light grey colour, demonstrated below. Source [1] Grey top shells may be found in great abundance on rocky shores of Southwest England. Their significant number makes the grey top shell an important component of the rocky shore ecosystem, affecting numbers of other organisms, predators and producers (plants). [2] I chose to study grey top shells as opposed to other organisms such as limpets or periwinkles for the reasons stated above. The species is found in large numbers and the top shell is recognisable with light purple and grey bands spanning its shell. It is therefore distinguishable from the darker periwinkle and purple top shell. [6] This will avoid misidentification and should provide fair and accurate results from which conclusions may be made. [3] The rocky shore may be split into three distinctive zones, the Supra-littoral zone, meaning above water, also known as the ‘splash zone’, the littoral zone and sub-littoral zone meaning below water. Contrasting biotic (living) and abiotic (non-living) conditions may be found in these zones owing to differences in time submerged by seawater. [2] [4] Several stressors act upon all organisms of the seashore. These include desiccation, a process where an organism loses water (and nutrients) from its body, extremes of temperature, competition from other organisms, light intensity, salinity, wave action, disturbance and pollution. The extent to which these stressors affect an organisms’ survival relies on the organisms’ position on the seashore. Different stressors have been


10

proven to act more in specific zones. The specific organisms’ ability to withstand stressors is the other vital factor affecting survival. [2] [5] Desiccation is more likely to influence survival of grey top shells higher on the rocky shore as this zone is rarely submerged in water. The lower littoral zone on the other hand experiences longer exposure to seawater and grey top shells have less chance of drying out. This will increase the number of top shells found lower on the shore. [5] Extremes of temperature are more likely to occur higher on the rocky shore. Seawater remains at a more constant temperature than land due to its high volume and high albedo. (Reflectivity of the surface) High temperatures in the upper littoral and supra-littoral zones are more likely to denature top shells enzymes resulting in death. This will reduce the number of grey top shells found on the upper shore. More constant temperatures sustained closer to the sea will be less able to denature the grey top shells’ enzymes. Light intensity may affect the amount of seaweed present affecting the amount of food available to the top shell. Top shells feed mainly on simple seaweed, microorganisms and detritus [1] Spearman's Rank Correlation is a technique used to test the direction and strength of the relationship between two variables. [7] A figure is calculated between -1 and +1, indicating a positive or negative correlation between two variables. The closer the figure is to -1 or +1, the stronger the correlation between variables. I will use this technique to test the strength of relationship between the dependant variable (Number of top shells) and independent variable (Distance from the sea wall). This technique will provide a quantitative figure that may conclude if distance affects the number of grey top shells. Null Hypothesis: Distance from the sea wall will have no effect on the number of grey top shells recorded. Spearman’s rank correlation will show no correlation between distance from the sea wall and the number of top shells recorded. Working Hypothesis: Results will show that as distance from the sea wall increases the number of grey top shells will increase. Spearman’s rank will highlight positive correlation between the two variables. Bibliography: [1]http://www.countryside-trust.org.uk/seashorecentre/seashore_wildlife/molluscs.htm [2] Marine Zonation theory Student Sheets [3] Collins pocket guide-Seashore of Britain and Northern Europe [4] http://www.glaucus.org.uk/Zones.htm [5] http://www.sfu.ca/~msr/Papers/BISC/littorinadesiccation.html [6] http://www.marlin.ac.uk/learningzone/species/LZ_Gibumb.htm [7] http://www.revision-notes.co.uk/revision/181.html


11

Commentary

R(a) The rationale, although rather straightforward, is clear and covers a number of biological principles in relation to the distribution of top shells. A more detailed discussion of the ecological principles of zonation and such factors as competition in each zone especially linked to mollusc distribution would be needed for the highest marks. Why does desiccation affect grey top shells more than other molluscs found higher on the shore? This is a clear R(a)6 and possibly 7.

R(b) There is a good range of sources quoted. They are clearly referenced in context. This could bring us to consider this to be good or very good. However, the highest marks would be generous since there is too little evidence that they have been used in the most effective manner. For example reference [5] contains some very useful information which would have helped to develop this rationale further. This is R(b) 7/8.

Overall R = 7.


12


Exemplar 2

Investigating the effect of ageing on bromelain activity in pineapple I am carrying out this investigation because the enzyme stem-bromelain is one that is particularly fascinating due to its medicinal properties and its possibility to become an extremely useful drug in treating many diseases. Bromelain is a general name for a family of sulfhydryl proteolytic (protein digesting) enzymes that are obtained from the pineapple plant. Stem bromelain is the name given to bromelain that is derived from the stem, and this is the most common type. Pineapples, containing stem bromelain, have been used as medicinal plants in several native cultures due to the fact that bromelain is thought to have many medicinal properties. It is a natural blood thinner and anti-inflammatory, which works by breaking down fibrin, a blood-clotting protein that can impede good circulation and prevent tissues from draining properly. Bromelain is also useful in relieving pain and speeding healing by blocking the production of the compounds that cause inflammation, allowing blood to move more easily to the traumatized area. It is also thought that bromelain aids digestive disorders due to its enzyme activity, as well as helping people with asthma thanks to its ability to reduce the thickness of mucus. Furthermore, currently research is being made into its use in the treatment of cancer. Hence, bromelain is a key enzyme in today’s world. The fact that this enzyme exists in pineapples, which are a part of many peoples’ diets, presents the question: Could it be that by eating pineapple regularly as part of your diet, you would be absorbing and taking advantage of its medicinal properties? In this case, it is interesting to investigate how the effectiveness of the enzyme varies under different conditions. One condition is the concentration of the enzyme. Enzymes are biological catalysts that speed up chemical reaction that would otherwise occur very slowly at room temperature. Proteases digest protein molecules due to the fact that they have complementary active sites. Therefore, if the enzyme concentration is increased, there are more active sites available for the reaction to occur. Hence, more enzyme-substrate complexes will be formed and the rate of reaction will be increased. Furthermore, at a higher concentration there are a higher proportion of particles in a certain area. Thus, the chance of collision between particles is greatly increased. In turn, this results in an increase in the probability that enzyme and substrate molecules will find each other and form enzyme-substrate complexes. Therefore, more enzyme-substrate complexes are formed in a certain time, and so more products are produced in that time. Hence, the rate of reaction is speeded up. The aim of this investigation is to discover if the age of the pineapple affects the concentration of the enzyme and therefore affects the rate at which it digests the protein. If the results of the experiment show that the age of the pineapple does affect the performance of the enzyme, then this could suggest that it may be preferable to eat pineapple of a certain age. A further use of the enzyme stem-bromelain is as a meat tenderiser. Hence, the way that the concentration of the enzyme varies the action of the enzyme could be of is interest in this industrial process. Therefore, this experiment is highly topical due to stem-bromelain’s many uses, and so the results will cause much discussion.


13

www.greatvistachemicals.com/biochemicals/bromelain.html Date: October 2004 www.thorne.com/altmedrev/fulltext/bromealin1-4.html Date: October 2004 http://www.zooscape.com/cgi-bin/maitred/GreenCanyon/questp415668/jornad1.25866175 Date: October 2004 www.edexcel.com/VirtualContent/24971.pdf Date: October 2004 Author: Salters Nuffield Advanced Biology Date: 2002 Title: AS Student book 1 Page: 77 Author: Salters Advanced Chemistry Date: 2000 Title: Chemical Storylines Page: 160 Author: John Adds, Erica Larkcom, Ruth Miller, Robin Sutton Date: 3/2000 Title: Tools, Techniques and Assessment in Biology. A course Guide for Students and Teachers Page:117-118

Commentary

R(a) There is some attempt to establish a rationale behind the investigation by giving the background to bromelain as a protease. However, beyond this it is very limited for A2 level. There is a cursory description of enzyme action and a brief mention of concentration effects, which does not get beyond modest AS level. Above all this is very general, there is no attempt to explain the main point of the investigation, which is how ageing might affect the concentration of the enzyme. This might just reach R(a)3 but is weak.

R(b) The range of sources is very limited. Several are simply A Level texts, one is Edexcel’s own website but with no direct reference to bromelain and two others are merely commercial sites selling bromelain as a product. Even checking the Interpreting and evaluating section revealed no further useful references. This reaches R(b)3.

Overall R = 3.


14


Exemplar 3

Investigating contrast sensitivity in humans Abstract: This project was designed to investigate the effect of contrast on eyesight to see how much this affects night driving. Eyesight tests were carried out using two modified 20/20 eye charts, one with black letters and one with grey. The results showed that people could read more lines on the high-contrast chart, agreeing with the hypothesis. Also, those with apparent perfect vision on the high-contrast chart had a range of readings on the low-contrast chart. Experimental hypothesis: The greater the contrast between letters and their background, the more letters read on the eye chart. Null Hypothesis: There will be no difference in the amount of letters read on a high-contrast eye chart and a low-contrast chart. Research and Rationale: This experiment aims to investigate the effect contrast sensitivity has on our eyes and how this could be applied to the dangers of night driving. On a normal 20/20 eye chart, there is high contrast between the black letters on the white background. Therefore this type of eye test only refers to high contrast situations unlike everyday images, which consist of all contrasts [Appendix 1]. Therefore the 20/20 eye chart cannot strictly be compared to our normal vision. Contrast sensitivity is the ability to discern an object from its background [Appendix 2]. Everything we see is split up into spatial frequencies or channels. Each channel, or vision cell, is a different size and has a different function. For example, there are channels for size, contrast and shape. The information from all the channels is transmitted to the brain and combined to form a complete picture. Large channels only take in information about shape, such as the shape of a face, whereas small channels filter information about the details of that face [Appendix 1]. Small channels are used when reading a normal high-contrast 20/20 eye chart; therefore only one type of channel is being tested. The results from the investigation can be applied to the dangers of night driving or in foggy conditions. Low light levels reduce contrast between objects, greatly affecting the sharpness of our vision. This increases the risk of an accident at night time because it becomes harder to distinguish between, for example, the colours of road signs. It also shows the importance to other road-users, such as cyclists, of wearing high-contrast luminous clothing for their own safety and general awareness of vehicle drivers’ limited vision.


15

Appendices: Appendix 1: www.contrastsensitivity.net — Date accessed: 25/08/04 Appendix 2: ‘Eye Health’ by Sandra Salmans Appendix 3: www.cquest.utoronto.ca/psych/psy280f/ch5/sf.html Appendix 4: www.cquest.toronto.edu/psych/psy316s/patternGif/frequency.gif — Date accessed: 31/10/04 Appendix 5: www.lighthouse.org/research_spatial.htm — Date accessed: 31/10/04 Appendix 6: www.cg.tuwien.ac.at/research/these/matkovic/node20.html — Date accessed: 31-30-04 Appendix 7: Biological Sciences Review — Janet Marsden

Commentary

R(a) This rationale is short and concise. Whilst it would benefit from a more detailed discussion, it is original and well-researched.

Note: this section is also judged on the use of this rationale ‘in informing the interpretation of results.’ In this case there was extensive further use of the reference sources in the interpretation of the data, which included both quotes from sources and personal analysis. R(a) 9/10 taking into account evidence from interpreting data.

R(b) The range of sources here is excellent. It includes both text materials and web-based sources. There is reference to academic papers and these have been used effectively in the report. ‘Appendices (2) and (7) are not referenced accurately so prevent the award of a maximum. R(b) 9/10.

Overall R = 9/10.

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18

Notes on planning

This is the single most important criterion in determining the success of an investigation. Important omissions in this section can often place severe limitations on a student’s opportunities to meet other criteria to a high standard.

a. Characteristics of a successful hypothesis (see also Ideas for Investigations)

• simple clear and unambiguous

• addresses only one variable

• includes an indication of statistical analysis, eg ‘there is a significant difference…’ ‘there is a significant correlation…’ ‘there is a significant association…’

• has a sound basis in A2 level biology

• in fieldwork is more likely to consider only one species.

b. Control of variables

This will vary considerably according to context. For higher marks, there must be clear evidence of progression from GCSE or AS level to A2. Weak attempts at controlling important variables such as light intensity or temperature by ‘leaving them on the same window sill’ or ‘at room temperature’ cannot support the awarding of higher marks.

In fieldwork, some variables cannot be easily manipulated, it would be expected that students will consider such options as selection of sampling sites to ensure that the effects of some variables were reduced and new ones were not introduced.


19

Planning

Exemplar 1

The effect of position on the rocky shore on the number of grey top shells Planning and Method: Firstly, I chose to carry out a series of line transects between the sea wall and the sea to record changes in numbers of grey top shells at varying distances from the sea wall. I chose a systematic sampling method as opposed to a random sampling method, to ensure all areas of the rocky shore were considered, providing more representative results. I planned therefore to carry out transects five metres apart, in parallel on the rocky shore. Apparatus planned for the experiment included a tape measure, a metre rule, a quadrat and a data logger. The tape measure would be used to map the transects line and to identify where each quadrat should be laid. The metre rule would be used to ensure transect courses are five metres apart. The quadrat would be laid at specific distances on the transect line and used to count the number of top shells, other species and percentage water cover. The data logger would finally be used to record temperature and light intensity at each quadrat on each of the five transects. I began work by carrying out a preliminary investigation, firstly to identify the speed at which capture of data could progress thus allowing me to calculate the number of transects I could complete. This also ensured transects could be completed before high tide. Rapid capture of results is paramount to ensure fair, reliable results are obtained. All other variables where possible should remain constant so only the independent variable, (distance from sea wall) is changed. Grey top shells are migratory and changes in tide and time of day is known to affect the position of grey top shells on the rocky shore. [1] The preliminary investigation enabled me to work out the size of intervals between quadrats where data would be collected. These distances had to be equal in size to observe how the number of top shells changes. Preliminary work enabled me to work methodically so keeping the method of data capture identical on each transect. In each quadrat, rocks were turned to ensure all top shells were included in the results. This method was adopted throughout data collection. The data logger was always held at the same height, 20cm above the ground. I always stood back to read the data logger. This avoided my shadow influencing the light intensity reading. The quadrat was always laid the right-hand side of the measuring tape to ensure the sampling method remained systematic throughout.

Commentary

P(a) Details of the planning process are very vague. It is difficult to discern how this differs from a premeditated group exercise and an examiner or moderator would wish to check other students in the centre to ensure this was not the case. This might just make P(a)3-6.

P(b) There is no real risk assessment despite the fact there are some obvious issues on a rocky shore. P(b) 0-2.

P(c) The account lacks any real evidence of a trial experiment (this is backed up by the poor data range seen in O) it is difficult to go beyond P(c) 0-2.

Overall P = 1 as P(b) has been ignored.


20

Planning

Exemplar 2

Investigating the effect of ageing on bromelain activity in pineapple Trial experiment: The aim of the trial experiment is to investigate which method of measuring the rate of digestion is more successful. In addition, it aims to act as a practice for the main experiment. Hence, any necessary modifications can be made to improve the accuracy and results of the final experiment. Method 1: 1. Prepare petri dishes containing gelatine 2. Using a cork borer, remove 3 circular discs from the gelatine in the petri dish. Be

sure to spread these wells evenly around the dish. 3. Cut a portion of 2 cm3 from the pineapple. Be sure to note the age of this piece of

pineapple. 4. Place the section of pineapple in a pestle and mortar and add 3 cm3 of distilled

water. Then mash the contents of the bowl until there is sufficient juice to fill the 3 holes.

5. Fill the holes in the petri dish with the pineapple solution, using a pipette. Be sure to label the gelatine plate for future reference.

6. Leave the gelatine plate with pineapple juice for 24 hours. 7. After 24 hours, measure the diameter of the hole (clear area). Include in the

diameter the initial hole made by the cork borer. Method 2: 1. Fill up a 50 cm3 measuring cylinder with gelatine. 2. Repeat stages 3 and 4 from the method above. 3. Add 2 cm3 pineapple juice to the top of the gelatine. 4. Leave the gelatine with the pineapple juice for 24 hours. 5. Re-measure the height of the solid gelatine. The level of the gelatine should drop,

as it becomes clear liquid due to digestion.

Results: Method 1:

Diameter of clear liquid (cm) Age of pineapple (days)

Diameter of original hole

(cm) Repeat: 1 2 3

1 1 1.3 1.4 1.4 Method 2:

Height of gelatine after being subjected to pineapple juice (cm3)

Age of pineapple

(days)

Original height of gelatine

(cm3) Repeat: 1 2 3 4

4 50 49.8 49.5 49.8 49.5


21

Both of these methods worked well however, it was decided to use method 1. The first reason for this was that a ruler gave a more accurate measurement than a 50 cm3 measuring cylinder. Furthermore, it was decided that in method 2, when using a measuring cylinder, it was harder to distinguish between the pineapple juice and the water produced, and where the line of the solid gelatine started. Hence, measuring the change in height was found slightly more difficult than using a ruler and a petri dish, as in method 1. The trial experiment also showed up any improvements that could have been made to improve the final experiment. • It was very difficult to grind the pineapple in the pestle and mortar when the

pineapple had been cut from the white part (centre) of the pineapple slice. Hence in future, this part should not be used.

• The experiment should be kept in the fridge to ensure that a constant temperature is maintained, thus ensuring accurate results. This is important because temperature is another variable which affects how enzymes work, and in order to ensure a fair test, all the variables other than the dependent and independent variable need to be kept constant.

• The change in the diameter and height from the original was very small, and hence it was decided that the 3 cm3 water should not be added to the section of pineapple in the pestle and mortar.

• Another reason for not using the water was that, when the pineapple juice was being put into the wells in the gelatine plate, often it was the liquid, which was mainly water that was easiest to pipette. However, by the time the last well was filled, only lumps of pure pineapple were left. Hence, the concentrations of pineapple were different in different wells, and so it was not a fair test. In order to eliminate the problem of having lumps of pineapple that would produce unfair and inaccurate results, an extension of the trial experiment was carried out. This was to see whether filtering the mashed pineapple solution would improve the accuracy of the results. Hence, the experiment in method 1 was repeated, however between stages 4 and 5 the pineapple solution was filtered using glass wool. The result of this mini-experiment was that the pineapple juice produced was not only easier to handle, due to the lack of lumps, but also it meant that the line between the solid gelatine and water, after digestion, was clearer. In addition, using glass wool resulted in the concentration of pineapple, and therefore enzyme, in the juice was constant. Therefore, the results were more accurate.

Procedure: 1. Prepare 10 petri dishes containing gelatine. 2. Using a cork borer, remove 3 circular discs from the gelatine plate and measure the

diameter of each hole. Be sure to evenly spread out the holes to allow the diameter of the hole to increase. In addition, use the same cork borer for all of the holes to ensure a fair test.

3. Cut a portion of pineapple which measures 2 cm3. 4. Place this section of pineapple in a pestle and mortar, and mash until enough liquid is

formed to fill the 3 holes.


22

5. Put glass wool into the neck of the filter funnel, and place this in the top of the conical

flask. Then filter the juice through the glass wool. When working with the glass wool goggles and gloves should be worn. In addition, it should be handled using tweezers.

6. Fill the hole in the petri dish with the pineapple solution using a pipette. Be careful not to overfill the hole, as this will disrupt the results.

7. Leave the gelatine plate with pineapple juice in the fridge for 24 hours. This maintains a constant temperature, which allows a fair test. When transporting the plate be careful not to spill the pineapple juice so that it overruns the hole. Also, after digestion, take care not to spill the water as this may make you think that the diameter is wider than it is. This would disrupt the results by giving higher results than necessary

8. After 24 hours, measure the diameter of the clear liquid area. Include in the diameter the initial hole made by the cork borer. To ensure a fair test, always measure the diameter at the widest point.

9. Work out an average diameter of the clear area. 10. Repeat stages 3 — 9 with each age of pineapple. 11. Using your results, perform the Spearman’s rank of correlation coefficient statistical

test. Accuracy: In order to ensure a fair test, many measures were taken. • All of the variables excluding the dependent and independent variables must be kept

constant to ensure that there is no external influence affecting the results. An example of this in the method is that a fridge will be used to store the gelatine plate, which means that there is a constant temperature.

• The same cork borer will be used for every gelatine plate. • The pineapple juice will be filtered to ensure that the concentration of pineapple juice

is the same for each repeat. • The diameter of the clear liquid will always be measured at the widest point, which

means that there are no biased results. • The experiment will be repeated 3 times and an average will be calculated. This should

eliminate any anomalies and mean that the results are to the highest possible standard. Risk assessment: • Care must be taken when using the sharp knife to cut the pineapple. • Glass wool: Irritant

Pure pineapple juice

100cm3 conical flask

Filter funnel

Glass wool

Ground pineapple


23

Commentary

P(a) There is a clear plan of action leading to a trial phase. Some important variables are discussed but not all important ones, eg control of grinding process, position of sample from fruit? What is a suitable time scale? P(a) 3-6.

P(b) This is a low risk procedure and there is a very basic assessment. Whilst this is thin it would not be used to limit marks if other sections were of high quality.

P(c) The trial is used in some ways to inform the final methodology but its effectiveness is limited by its limited scope. P(c) 3-6.

Overall P = 5/6.


24

Planning

Exemplar 3

Investigating contrast sensitivity in human eyesight

A trial experiment was carried out to find the best contrast type and distance from the charts, and the need for extra lighting. Two participants, aged 17, with good eyesight took part. They read aloud letters on each eye chart as far as possible, and the last line read was recorded. Three eye charts were used: one covered in two sheets of greaseproof paper, one covered with one sheet, and one without. The chart covered with two sheets did not work because of unequal contrast variations. The greaseproof paper was then glued to the eye chart but this wrinkled and made it worse. Trials showed the best way to effectively alter the contrast of the eye charts was black letters on a white background for one chart and grey letters for the other. The participants read both charts from various distances and 6m was decided upon. No extra lighting would be needed for the main experiment because this caused a yellow-light to be cast on the charts, reducing contrast. [Details in appendices]. A Mann Whitney U Test will be used to analyse the data, which will compare the median of the two sets of data gained for each eye chart. Trial Experiment results: Here are the results for the original eye charts, covered in 1, 2 or no sheets of greaseproof paper to vary the contrast. The subject stood 6m from the eye chart and normal lighting was used.

Lowest line read on chart*

Contrast level

Subject 1

Subject 2 2 sheets of greaseproof paper (low contrast) 6 7 1 sheet of greaseproof paper 9 10 No greaseproof paper (high contrast) 10 10 * With line 1 being at the top of the chart with the largest letters and line 10 being the smallest letters. These results indicate that it would be more effective to compare an eye chart with high-contrast (no greaseproof paper) against one with 2 sheets of greaseproof paper in order to get a significant difference in results. The distance from the eye chart was altered to find the best distance to test vision from as this was to be kept constant. Vision was tested at 5, 6, 7 and 8m from the normal eye chart with high-contrast (no greaseproof paper added) under normal lighting. Here are the results:


25


Distance from eye chart (m)

Subject 1

Subject 2 5 10 10 6 10 10 7 6 7 8 6 6

* With line 1 being at the top of the chart with the largest letters and line 10 being the smallest letters. I decided to set the distance at 6m because the two participants used in the trial had good eyesight and they could not read the bottom line at 7m. The final part of my trial experiments was to test the effect of adding extra lighting to the eye chart. I tested the subjects’ vision on the normal high-contrast chart at 6m with normal lighting and then with extra lightning. Here are the results:


Type of lighting used Subject 1 Subject 2 Normal lighting 10 10 Extra lighting 7 6 * With line 1 being at the top of the chart with the largest letters and line 10 being the smallest letters. These results therefore show me that adding extra lighting reduces the subject’s ability to read the letters on the chart. Therefore I have decided not to add extra lighting to the eye charts because it worsens vision. Planning: A trial experiment was carried out to find the best contrast type and distance from the charts, and the need for extra lighting. Two participants, aged 17, with good eyesight took part. They read aloud letters on each eye chart as far as possible, and the last line read was recorded. Three eye charts were used: one covered in two sheets of greaseproof paper, one covered with one sheet, and one without. The chart covered with two sheets did not work because of unequal contrast variations. The greaseproof paper was then glued to the eye chart but this wrinkled and made it worse. Trials showed the best way to effectively alter the contrast of the eye charts was black letters on a white background for one chart and grey letters for the other. The participants read both charts from various distances and 6m was decided upon. No extra lighting would be needed for the main experiment because this caused a yellow-light to be cast on the charts, reducing contrast. A Mann Whitney U Test will be used to analyse the data, which will compare the median of the two sets of data gained for each eye chart.


26

Method: For the main experiment, two modified eye charts were positioned next to each other on a plain white wall, at the same height. Two different eye charts, with the same font and letter sizing, were used so that participants did not memorise the letters. Using a meter ruler, a line was marked on the floor 6m from both eye charts to keep the distance constant. The lighting was kept constant because the regular room lights were lit throughout. Using an opportunity sample for convenience, 30 participants all aged between 17-18, with equal numbers of males and females, were used. Before the test, participants filled in a short form about their eyesight details [see appendices]. Subjects were then asked to remove any form of visual aid (spectacles or contact lenses) so that their true vision could be tested without it being modified. Each participant read aloud, starting from the top line, each letter on the low-contrast chart (grey letters) as far as possible. The last line read was recorded. They then read the letters from the high-contrast (black letters) chart in the same way and the results were recorded. Risk Assessment: All participants’ details used in this experiment are kept anonymous for confidentiality reasons. Any visual aids that were removed for the duration of the experiment were kept nearby in case of emergency. Otherwise this is a low risk procedure.

Commentary

P(a) This clearly meets 7-9 criteria as there is clear evidence of a trial phase with some results used to inform the main method. There is some discussion on control of variables but poor control of sampling is suspect and there is no evidence that those with eye defects were recorded or checked. We are not sure what happens when a line is partially recognised. However there is sufficient here to consider the highest mark in this range.

P(b) Again this risk assessment is simple but it is important to ask what else should have been considered. If the answer is very little, as it is here, then higher marks can be supported.

P(c) The trial is well thought out and used to inform the plan.

There is sufficient here to consider the highest mark range as there is evidence of ingenuity and modification of apparatus but there is not really enough attention to detail in control of variables to warrant a mark of 10-11.

Overall P = 9.

Tuto

r su

ppor

t m

ater

ials

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dexc

el G

CE in

Bio

logy

— S

uppo

rt b

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or U

nit

6 (6

BI06

) —

Is

sue

1 —

Nov

embe

r 20

08 ©

Ede

xcel

Lim

ited

200

8

27

Obs

ervi

ng a

nd r

ecor

ding

Ass

essm

ent

crit

eria

Le

vel o

f re

spon

se

a)

focu

ses

on a

ccur

ate

reco

rdin

g an

d ta

bula

tion

of

data

.

b)

focu

ses

on t

he s

elec

tion

of

a su

itab

le r

ange

of

read

ings

and

an

appr

opri

ate

resp

onse

to

anom

alou

s re

adin

gs d

urin

g da

ta

colle

ctio

n.

Mar

k ra

nge

a)

Som

e ap

prop

riat

e m

easu

rem

ents

and

obs

erva

tion

s ar

e re

cord

ed,

whi

ch a

re a

dequ

ate

for

the

met

hod

used

and

rea

sona

bly

accu

rate

.

b)

Ther

e is

som

e re

peat

ing

or c

heck

ing

of v

alue

s ob

tain

ed.

At

this

lev

el t

here

is

just

suf

fici

ent

data

to

mak

e ba

sic

conc

lusi

ons

link

ed t

o th

e hy

poth

esis

. Th

e le

vel

of a

ccur

acy

is j

ust

acce

ptab

le f

or a

n A

2 in

vest

igat

ion.

0–2

mar

ks

a)

Mea

sure

men

ts a

nd o

bser

vati

ons

are

reco

rded

met

hodi

cally

and

acc

urat

ely

in a

ppro

pria

te u

nits

, an

d so

me

thou

ght

is g

iven

to

prec

isio

n an

d re

peat

abili

ty.

b)

A re

ason

able

num

ber

and

rang

e of

obs

erva

tion

s an

d m

easu

rem

ents

are

car

ried

out

. An

y an

omal

ous

resu

lts

are

note

d. T

here

is

som

e ap

prop

riat

e m

odif

icat

ion

of p

roce

dure

s fo

r da

ta c

olle

ctio

n if

nec

essa

ry.

Resu

lts

wil

l be

rec

orde

d in

sui

tabl

e ta

bles

wit

h cl

ear

head

ings

. U

nits

sho

uld

be c

lear

ly i

ndic

ated

in

the

head

ings

onl

y an

d sh

ould

fo

llow

the

Inst

itut

e of

Bio

logy

gui

deli

nes.

It i

s no

t ne

cess

ary

to f

ind

anom

alie

s w

here

the

y cl

earl

y do

not

exi

st b

ut s

ome

com

men

t on

thi

s w

ill

be e

xpec

ted.

Jud

gem

ents

on

the

exte

nt o

f da

ta a

nd r

easo

nabl

e nu

mbe

r of

rep

eats

sho

uld

be v

iew

ed i

n th

e co

ntex

t of

th

e in

vest

igat

ion.

In p

arti

cula

r, i

s th

ere

a re

ason

able

am

ount

of

data

to

mak

e a

mea

ning

ful

judg

emen

t on

the

hyp

othe

sis

bear

ing

in

min

d w

hat

coul

d be

exp

ecte

d fr

om a

n A

Lev

el s

tude

nt i

n th

e ci

rcum

stan

ces.

Stu

dent

s us

e co

mm

on s

ense

in

chec

king

the

ir d

ata

as i

t is

col

lect

ed,

to i

dent

ify

and

poss

ibly

rep

eat

expe

rim

ents

if

unus

ual

figu

res

or r

eadi

ngs

are

obta

ined

.

3–6

mar

ks

Obs

ervi

ng

and

reco

rdin

g

a)

Obs

erva

tion

s an

d m

easu

rem

ents

are

car

ried

out

ove

r a

suit

able

ran

ge o

f va

lues

and

con

diti

ons.

Suf

fici

ent

obse

rvat

ions

are

m

ade

to a

llow

a c

oncl

usio

n. N

umer

ical

res

ults

are

rec

orde

d to

an

appr

opri

ate

degr

ee o

f pr

ecis

ion.

b)

Mea

sure

men

ts a

nd o

bser

vati

ons

are

repe

ated

as

appr

opri

ate.

Any

ano

mal

ous

resu

lts

are

note

d an

d in

vest

igat

ed.

If p

robl

ems

aris

e in

the

mak

ing

of m

easu

rem

ents

or

obse

rvat

ions

, pr

oced

ures

are

ada

pted

to

ensu

re d

ata

is r

elia

ble.

The

rang

e of

val

ues

or c

ondi

tion

s is

wel

l-m

atch

ed t

o th

e in

vest

igat

ion.

Thi

s m

ay b

e ju

stif

ied

by c

heck

ing

a ru

nnin

g m

ean

or b

y re

fere

nce

to t

he r

equi

rem

ents

of

a ch

osen

sta

tist

ical

tes

t. T

able

s of

col

lect

ed o

r m

anip

ulat

ed d

ata

quot

e fi

gure

s to

a l

evel

of

accu

racy

tha

t ca

n be

jus

tifi

ed b

y th

e m

etho

ds e

mpl

oyed

.

The

tabu

late

d da

ta r

efle

cts

good

pra

ctic

e in

acc

urat

ely

iden

tify

ing

poss

ible

ano

mal

ies

and

show

s so

und

scie

ntif

ic p

ract

ice

in

deal

ing

wit

h va

riat

ions

. Th

ere

is o

bjec

tive

ana

lysi

s ra

ther

tha

n a

dete

rmin

atio

n to

con

form

to

a pr

econ

ceiv

ed m

odel

.

7–8

mar

ks


28

Observing and recording

Exemplar 1

The effect of position on the rocky shore on the number of grey top shells Results: Transect 1

Distance from

Number Grey

Temp(°C) Light intensity

No. limpets % water cover

Sea Wall (M) Top Shells (lux) 0 0 18 8200 0 0 5 0 21.2 6850 0 0 10 0 18 8750 0 0 15 2 20.6 8050 0 0 20 3 19.8 13000 0 0 25 9 19.8 15000 2 0 30 4 21.2 11500 1 0 35 5 19.8 3050 0 0 40 2 21.6 13000 0 5 45 2 19.8 1750 0 20 50 13 21.4 12000 8 50

Transect 2

Distance from

Number Grey

Temp (°C) Light intensity


Sea Wall (M) Top Shells (lux) 0 0 19.4 1400 0 0 5 0 19.4 4200 0 0 10 0 19.2 6000 0 0 15 1 19.6 8900 0 0 20 3 20 7900 1 0 25 2 18.8 5800 0 0 30 6 18.8 5000 1 50 35 5 19 4900 3 0 40 7 19.4 5000 4 0 45 17 20 4300 9 20


29

Transect 3

Distance from

Number Grey

Temp (°C) Light intensity


Sea Wall (M) Top Shells (lux) 0 0 22.2 8200 0 0 5 0 22.2 10500 0 0 10 0 22.2 11500 0 0 15 0 22 12500 0 0 20 1 21.6 10000 1 0 25 2 21.6 14000 1 10 30 6 21.4 23500 2 10 35 5 21.7 20000 6 25 40 8 21.4 20000 4 40

Transect 4

NOTE transects 4 and 5 data omitted from exemplar

Commentary

O(a) Measurements are recorded accurately with a minor error of 22.00C. Units are in headings and generally accurate. Precision is fine but we are not clear exactly what % water cover is. The range is questionable with three of the readings having no topshells. It is not clear why some data has been recorded (limpets? water cover?) when it does not seem to link directly to the hypothesis. O(a) At the upper end of the 3-6 range.

O(b) There were 4 transects so plenty of repeats. There is no reason to repeat readings but procedure could have been modified to eliminate so many zero readings. O(b) strong 3-6.

Overall O = 6.


30


Exemplar 2

Investigating the effect of ageing on bromelain activity in pineapple Results:

Diameter of clear liquid (cm) Age of pineapple (days)

Diameter of original hole

(cm) Repeat: 1 2 3

1 1 1.3 1.4 1.4 2 1 1.4 1.4 1.4 3 1 1.4 1.4 1.5 4 1 1.5 1.6 1.6 5 1 1.7 1.6 1.7 6 1 1.8 1.8 1.8 7 1 1.9 1.8 1.8 8 1 1.6 1.7 1.8 9 1 1.9 1.8 1.7 10 1 1.7 1.7 1.8

Increase in diameter (mm) Age of pineapple

(days) Repeat: 1 2 3 1 3 4 4 2 4 4 4 3 4 4 5 4 5 6 6 5 7 6 7 6 8 8 8 7 9 8 8 8 6 7 8 9 9 8 7 10 7 7 8

Commentary

O(a) The data is recorded methodically but accuracy is suspect. Although there is no evidence that these wells were circular and therefore we could expect repeated readings of the diameter for accuracy. It is clear that the edge of the digested gelatine is indistinct and therefore given the very small differences recorded the data is unreliable. The lack of processing to give areas would be considered under interpreting and evaluation criteria. O(a) 3-6 weak.

O(b) There are some significant questions over the time scale for this. Differences are marginal at times and longer intervals would have been more effective. This would limit marks to O(b) 3-6.

Overall O = 4.


31


Exemplar 3

Investigating contrast sensitivity in humans

Results:

Results for high-contrast eye chart

Lowest line read on eye

chart Number of Males Number of Females

0 0 0 1 0 0 2 0 0 3 0 0 4 1 0 5 0 3 6 1 0 7 0 1 8 0 0 9 2 1 10 11 10

Total 15 15

Results for low-contrast eye chart:



0 1 0 1 1 1 2 0 0 3 0 2 4 1 2 5 2 2 6 6 4 7 4 3 8 0 1 9 0 0 10 0 0

Total 15 15


32

Commentary

O(a) This is straightforward data but this need not limit marks if the investigation is well-founded in A2 biology. The data is organised into simple size classes to allow more detailed analysis. Whilst it is clearly ‘fit for purpose’ it is not totally clear that this is the last complete line that could be read. Given its simple nature we can be justified in expecting this to be clearly stated.

O(a) At the upper end of the 3–6 range.

O(b) Again the measurements will yield some useful information directly linked to the

hypothesis but we might expect more measurements to have been taken.

O(a) At the upper end of the 3-6 range.

Overall O = 6.

Tuto

r su

ppor

t m

ater

ials

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el G

CE in

Bio

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ookl

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or U

nit

6 (6

BI06

) —

Is

sue

1 —

Nov

embe

r 20

08 ©

Ede

xcel

Lim

ited

200

8

33

Inte

rpre

ting

and

eva

luat

ion

Ass

essm

ent

crit

eria

Le

vel o

f re

spon

se

a)

focu

ses

on s

tati

stic

al a

naly

sis

of t

he r

ecor

ded

data

and

its

inte

rpre

tati

on.

b)

focu

ses

on t

he u

se o

f bi

olog

ical

kno

wle

dge

and

unde

rsta

ndin

g to

inte

rpre

t th

e da

ta.

c)

focu

ses

on t

he a

bilit

y to

dra

w s

umm

ary

conc

lusi

ons

and

eval

uate

the

ir v

alid

ity

by a

dis

cuss

ion

of t

he li

mit

atio

ns o

f th

e ex

peri

men

tal t

echn

ique

s em

ploy

ed.

Mar

k Ra

nge

Inte

rpre

ting

an

d ev

alua

tion

a)

Ther

e is

som

e da

ta p

roce

ssin

g. S

tati

stic

al a

naly

sis

is o

nly

com

plet

ed w

ith

deta

iled

guid

ance

. Ap

plic

atio

n of

cal

cula

ted

stat

isti

cal v

alue

s is

pre

sent

, th

ough

lim

ited

or

conf

used

.

b)

Ther

e is

an

atte

mpt

to

appl

y bi

olog

ical

pri

ncip

les.

c)

Som

e co

nclu

sion

s ar

e st

ated

. Th

ere

is s

ome

awar

enes

s of

the

lim

itat

ions

of

expe

rim

enta

l res

ults

and

con

clus

ions

.

Dat

a is

onl

y m

anip

ulat

ed in

the

sim

ples

t w

ay e

g th

e ca

lcul

atio

n of

tot

als.

A m

axim

um m

ark

of 2

wil

l be

app

lied

whe

re t

here

is n

o ev

iden

ce o

f st

atis

tica

l te

stin

g.

Biol

ogic

al k

now

ledg

e an

d un

ders

tand

ing

is a

ppli

ed t

o ex

plai

n tr

ends

and

pat

tern

s in

the

dat

a in

a v

ery

sim

ple

way

or

info

rmat

ion

is m

erel

y qu

oted

wit

h no

evi

denc

e of

its

app

lica

tion

to

the

tabu

late

d re

sult

s.

Ther

e is

a s

hort

sta

tem

ent

of c

oncl

usio

ns,

whi

ch a

re d

irec

tly

rela

ted

to t

he h

ypot

hesi

s.

Lim

itat

ions

are

dis

cuss

ed s

uper

fici

ally

and

are

con

cern

ed m

ainl

y w

ith

basi

c er

rors

.

0–3

mar

ks

Tuto

r su

ppor

t m

ater

ials

— E

dexc

el G

CE in

Bio

logy

— S

uppo

rt b

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or U

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6 (6

BI06

) —

Issu

e 1

— N

ovem

ber

2008

© E

dexc

el L

imit

ed 2

008

34

a)

D

ata

is p

roce

ssed

wit

h so

me

thou

ght

as t

o th

e ch

oice

of

met

hod.

The

cho

sen

stat

isti

cal t

est

may

be

inap

prop

riat

e or

pr

ovid

e lim

ited

ana

lysi

s of

the

sta

ted

hypo

thes

is.

Calc

ulat

ions

are

cle

arly

set

out

but

the

inte

rpre

tati

on o

f th

e ca

lcul

ated

va

lues

lack

s de

taile

d ex

plan

atio

n. S

ome

tren

ds a

nd p

atte

rns

are

iden

tifi

ed.

b)

Som

e at

tem

pt is

mad

e to

inte

rpre

t re

sult

s us

ing

biol

ogic

al p

rinc

iple

s an

d dr

aw c

oncl

usio

ns b

ased

on

expe

rim

enta

l res

ults

.

c)

Conc

lusi

ons

are

supp

orte

d by

res

ults

. Th

e lim

itat

ions

of

resu

lts

and

conc

lusi

ons

base

d up

on t

hem

, ar

e re

cogn

ised

.

It i

s ex

pect

ed t

hat

thes

e w

ill

be d

iscr

imin

atin

g cr

iter

ia.

To m

ove

to t

his

mar

k ra

nge

stud

ents

mus

t sh

ow t

hey

have

use

d a

suit

able

st

atis

tica

l te

st a

nd t

hat

they

hav

e a

basi

c un

ders

tand

ing

of i

ts m

eani

ng (

see

addi

tion

al n

otes

on

stat

isti

cal

test

ing)

.

Iden

tifi

cati

on o

f tr

ends

and

pat

tern

s is

sim

ple

but

does

go

beyo

nd j

ust

a w

ord

desc

ript

ion

of t

he d

ata.

App

lica

tion

of

biol

ogic

al k

now

ledg

e is

sou

nd b

ut l

acks

a d

etai

led

disc

ussi

on l

inki

ng i

t cl

osel

y to

the

tre

nds

and

patt

erns

des

crib

ed.

Dis

cuss

ion

of l

imit

atio

ns i

dent

ifie

s so

me

impo

rtan

t sh

ortc

omin

gs o

f th

e ap

para

tus

and

the

met

hods

em

ploy

ed b

ut l

acks

a d

etai

led

obje

ctiv

e re

view

.

Ther

e is

cle

ar e

vide

nce

of b

iolo

gica

l kn

owle

dge

and

unde

rsta

ndin

g ga

ined

fro

m i

niti

al r

esea

rch

bein

g ap

plie

d in

an

atte

mpt

to

expl

ain

the

find

ings

and

sup

port

any

con

clus

ions

.

4–6

mar

ks

a)

D

ata

are

proc

esse

d us

ing

appr

opri

ate

met

hods

tha

t re

veal

tre

nds

and

patt

erns

. Th

e ch

osen

sta

tist

ical

tes

ts a

re a

ppro

pria

te

to t

he d

ata

to b

e an

alys

ed a

nd t

he h

ypot

hesi

s to

be

test

ed.

Calc

ulat

ions

of

stat

isti

cal t

ests

are

cle

arly

set

out

and

in

terp

rete

d, u

sing

a n

ull h

ypot

hesi

s an

d a

5% c

onfi

denc

e le

vel w

here

app

ropr

iate

. Tr

ends

and

pat

tern

s ar

e id

enti

fied

.

b)

Resu

lts

are

inte

rpre

ted

usin

g bi

olog

ical

pri

ncip

les

and

conc

epts

of

Adva

nced

GCE

sta

ndar

d. R

elev

ant

biol

ogic

al p

rinc

iple

s ar

e ap

plie

d co

rrec

tly

thro

ugho

ut.

c)

Conc

lusi

ons

are

supp

orte

d by

res

ults

. Th

e lim

itat

ions

of

resu

lts

and

the

conc

lusi

ons

base

d up

on t

hem

, ar

e re

cogn

ised

and

ev

alua

ted.

Any

lim

itat

ions

of

the

proc

edur

e ar

e co

mm

ente

d up

on,

and

sens

ible

mod

ific

atio

ns a

re s

ugge

sted

.

To r

each

thi

s le

vel

the

who

le a

naly

sis

shou

ld b

e ac

cura

te a

nd o

bjec

tive

. St

uden

ts m

ust

have

sel

ecte

d th

eir

info

rmat

ion

care

full

y an

d ap

plie

d it

acc

urat

ely.

The

y sh

ould

avo

id s

wee

ping

gen

eral

isat

ions

and

dem

onst

rate

an

awar

enes

s th

at t

he c

oncl

usio

ns t

hey

mak

e ar

e li

kely

to

lead

to

othe

r qu

esti

ons

or a

re p

art

of a

wid

er p

atte

rn o

f in

tera

ctio

ns.

A c

onsi

dera

tion

of

lim

itat

ions

mus

t al

so i

nclu

de a

n an

alys

is o

f th

e un

derl

ying

pri

ncip

les

and

assu

mpt

ions

of

the

chos

en

met

hodo

logy

. Su

gges

tion

s fo

r m

odif

icat

ions

mus

t be

lin

ked

to s

uch

an a

naly

sis.

Col

lect

ing

mor

e da

ta o

r re

peat

ing

agai

n ar

e no

t su

gges

tion

s th

at c

an b

e gi

ven

cred

it a

t th

is l

evel

.

7–9

mar

ks


35

Notes on the use of statistics

a. Principles

There are no statistical tests named in the specification and it is not assumed that students will have knowledge of the detailed mathematical derivations of the different formulae.

The emphasis at this level is to introduce the principle of statistical testing as a progression from subjective analysis of data to some objective guidelines when considering how far collected data agrees or disagrees with the hypothesis under test.

b. What students are expected to demonstrate

(i) Their ability to select the correct form of statistical test appropriate to their hypothesis. It is highly recommended that this is an integral part of the plan.

(ii) An understanding of the use of a null hypothesis.

(iii) Their ability to tabulate data in the correct format for calculating their chosen statistical value.

(iv) Their ability to explain the meaning of any calculated test statistic in terms of 5% confidence limits, where appropriate, and its relationship to their stated hypothesis in their own words.

c. Types of statistical tests

There are three main types of test.

(i) Tests for a significant difference — typically a t-test or a Mann-Whitney U test.

(ii) Tests for a significant correlation — typically Spearman’s Rank test.

(iii) Tests for significant association or ‘goodness of fit’ — typically Chi-squared test.

Experience has shown that tests for significant difference and significant correlation account for over 95% of typical investigations at this level. Obviously, this is not an exclusive list and there are many other appropriate tests for use in different situations.

Very few investigations lead to chi-squared testing. This is because a chi-squared test needs to be carried out on categorical data. This is data that consists of counts, which are totalled, in distinct categories, eg red-eye/white eye, colour morphs of Litterinids on different algae, etc. It is not applicable to any data at the interval level of measurements, ie those we would regard as normal measurements of size, mass etc, nor is it a test of significant difference between two samples. This is simply because that, where we have only counts of categories, it is not possible to assess the magnitude of any differences.


36

d. Null Hypotheses

It is important for students to understand the importance of accuracy in their wording. There is a large difference in meaning between ‘There is no difference between….’ and ‘There is no significant difference, (at the 5% confidence level) between….’

The reasoning behind the use of a null value in hypothesis testing is as follows:

(i) Start with the assumption that the two means of your samples are the same.

(ii) Take sample measurements to find out what is the true situation.

(iii) Use a statistical test to find the probability of getting values at least as far apart as those shown in your data.

(iv) If this probability is low (less than 5 chances in 100) then we can say that the assumption made in (i) is not correct. (reject a null hypothesis).

Hence a null hypothesis is a consequence of the way the statistical test calculates the probability.

e. Using computer calculations

In many cases statistical calculations are rather tedious and a source of error and most scientists would use computer programmes to carry them out. This is acceptable provided that there is a clear indication of how the data has been processed and not just the recording of a single figure.

In practice this would mean including the tabulation used for processing, eg the spreadsheet if using Microsoft Excel or other programmes or the table of ranks for a Spearman’s Rank calculation.

Many commercial programmes also print out not only the test statistic but a formalised statement as to its meaning. It is strongly advised that students explain in their own words the meaning of the test statistic and continue to discuss exactly how this is linked to their hypothesis.

f. Further information

There are many useful books available including:

The OU Project Guide — Chalmers and Parker (Field Studies Council) ISBN 1 85153809 9

Maths for Advanced Biology — Cadogan and Sutton (Nelson) ISBN 0 17448214 0 The OU Project Guide contains a wealth of information that is highly relevant to those planning investigations or as a teacher’s reference. It has a particularly useful short summary of the requirements of many statistical tests, which form a useful guide at the planning stage.

Maths for Advanced Biology is shorter and targeted more as a student text.


37

Awarding high marks in interpreting and evaluation section(c)

The examiners will be looking for evidence of detailed and objective analysis in this section. Above all students will be expected to take a detailed look at their methodology and identify any limitations.

Note: limitations are not admissions of personal incompetence (‘ I might have misread the thermometer’ etc). The vital question to ask is: ‘No matter how carefully I carried out this procedure, what could still cause my repeat readings to differ’?

This might lead to such questions as, ‘Am I measuring exactly what I think I am?’ or ‘What other variables might be operating that I have not been able to control’?

More able students may then be able to analyse possible systematic or random errors.

For example, when using a colorimeter, failing to account for the solution by zeroing with a blank might lead to a systematic error which would be constant for all readings but might have a proportionally greater effect on lower or higher readings. However, a failure to ensure that all cuvettes were uniformly clean could lead to random errors where some readings of transmission might be lowered but not all.

Using this section to correct large errors of planning will only gain limited credit.

‘Sensible modifications’ should follow directly from this type of analysis of limitations. Simplistic suggestions concerning ‘more repeats’ or changing the range will only gain limited credit.


38

Interpreting and evaluation

Exemplar 1

The effect of position on the rocky shore on the number on grey top shells Transect 1 Distance Rank 1 No. Top Shells Rank 2 Difference Difference Squared

0 1 0 2 1 1 5 2 0 2 0 0 10 3 0 2 -1 1 15 4 2 5 1 1 20 5 3 7 2 4 25 6 9 10 4 16 30 7 4 8 1 1 35 8 5 9 1 1 40 9 2 5 -4 16 45 10 2 5 -5 25 50 11 13 11 0 0

Total 66 Correlation 0.67 Transect 2 Distance Rank 1 No. Top Shells Rank 2 Difference Difference Squared

0 1 0 2 1 1 5 2 0 2 0 0 10 3 0 2 -1 1 15 4 1 4 0 0 20 5 3 6 1 1 25 6 2 5 -1 1 30 7 6 8 1 1 35 8 5 7 -1 1 40 9 7 9 0 0 45 10 17 10 0 0

Total 6 Correlation 0.96 Transect 3 Distance Rank 1 No. Top Shells Rank 2 Difference Difference Squared

0 1 0 2.5 1.5 2.25 5 2 0 2.5 0.5 0.25 10 3 0 2.5 -0.5 0.25 15 4 0 2.5 -1.5 2.25 20 5 1 5 0 0 25 6 2 6 0 0 30 7 6 8 1 1 35 8 5 7 -1 1 40 9 8 9 0 0

Total 7 Correlation 0.94 Transect 4


39

Calculations for transects 4 and 5 omitted from exemplar Conclusion and Evaluation: Spearman’s rank correlation from results of the five transects clearly shows positive correlation between the two variables. This indicates that distance from the sea wall affects the number of grey top shells. Some correlation is strong, particularly in transects two, three and four with figures of 0.96, 0.94 and 0.89 respectively. These figures are close in proximity to +1 indicating the strong positive correlation. The independent variable, (distance from sea wall) impacts the dependant variable, (number of grey top shells) and proves the null hypothesis incorrect. It is clear that distance from sea wall has some effect upon the number of grey top shells. Justification for this strong positive correlation is not however clear. Excluding transect 3, temperature rose slightly as I moved away from the sea wall. This event was not predicted and may effect the number of top shells indirectly. Rising temperature away from the sea wall for example may increase enzyme activity of the molluscs, consequently more top shells would be found further from the sea wall. Raising temperature is demonstrated by the temperature change graph and is likely to be the effect of reduced shade from the sun away from the sea wall. The result suggests that time of submergence by seawater has a greater impact on desiccation than temperature. Greater time submerged by water further from the sea wall decreases the chance of an organism ‘drying out’. More accurate temperature data could have been captured had I had access to soil temperature thermometers. Soil/sand temperature is more likely affect top shells as the species have contact with this surface. The graph for light intensity shows a general increase with increasing distance from the sea wall. This could potentially impact the amount of food available to the grey top shell. More light for photosynthesis further from the sea wall may lead to a faster rate of photosynthesis. There are however several anomalous results for light intensity. This is likely to be the result of passing cloud cover. A greater number of recordings would be needed to confidently state any trend in light intensity that may affect the number of grey top shells. Equipment used was also very sensitive and data alters rapidly between sunshine and cloudy periods. There are several limitations to the original working hypothesis. A trend has been noticed that increasing distance increases the number of top shells. The graph also highlights however a more complex trend. Between 0-20M from the sea wall, there is a gradual increase in the number of top shells. There is then a peak at around 25M and a reduced number at 30-35M. The number then escalates rapidly in the lower littoral towards the sub-littoral zone. (Between 40-50M) This higher number at 20-25M may be the result of isolated rock pools creating ideal conditions for the grey top shells. Temperature in the pools would be warm but not too warm, water would prevent desiccation, Simple seaweeds and detritus would be an ideal food source. Submersion in the water may also provide added protection from predators.


40

There are several reasons why the graphs contain anomalous results. The main causes are likely to be natural (biotic and abiotic) differences. This may be the presence of rock pools, or particularly sheltered rock. There may be presence of a specific food source. There may even be more top shells in one area than another for safety in numbers. Top shells may group together for protection from predators. Humans may also affect numbers of top shells, particularly through trampling. There may also be limitations in the method of data collection. For example, changing tides permitted limited length transects. At times just 40M from the sea wall could be reached. If possible, I would have conducted transects in the sub-littoral zone to continue the line graphs and to gain a broader view of the number of grey top shells along the rocky shore. When counting the number of top shells in each quadrat in each transect, it is possible that shells were counted more than once or even overlooked. Rushing to obtain sufficient data before the tide changed, it is possible some shells were uncounted. When wet the grey top shell and other species such as the purple top shell and periwinkle change colour slightly. This may have led to misidentification of an organism.

Commentary

I(a) There is a correct statistical test which is clearly set out and directly linked to the main hypothesis but it lacks a clear explanation of its meaning and any reference to confidence limits. Some trends and patterns are identified but these are not always directly linked to the hypothesis. I(a) 4-6 weak.

I(b) This is a weak section. The overall attempt to interpret the data lacks a focus and tends to make isolated comments rather than a coherent explanation. The application of A2 biological principles is weak. I(b) 0-3.

I(c) Conclusions are confused and not always accurate. Most of the limitations are the result of poor planning or suggested mistakes and there is little valid suggestion for taking this further. I(c) 0-3.

Overall I = 3.


41

Interpreting and evaluating

Exemplar 2

Investigating the effect of ageing on bromelain activity in pineapple Analysis: The results will be analysed using the Spearman rank correlation test. This test was chosen due to the large number of results that were obtained during the experiment. Null hypothesis: There is no correlation between the age of pineapple and the increase in diameter of the clear area as a result of digestion. A scattergraph was drawn to show the relationship between the 2 variables. From this graph it could be seen that after the pineapple had reached the age of 7 days, the relationship between the 2 variables started to drop and the correlation no longer remained steady. Hence, it was decided to perform the Spearman rank correlation test only on the values up to 7 days of age. D = the difference between the 2 ranks

Age of pineapple (days)

Rank Increase in diameter

(cm) Rank D 4.2

1 2 3 1 1 1 1 2 4 5 -3 9 1 2 4 5 -3 9 2 5 4 5 0 0 2 5 4 5 0 0 2 5 4 5 0 0 3 8 4 5 3 9 3 8 4 5 3 9 3 8 5 9.5 -1.5 2.25 4 11 5 9.5 1.5 2.25 4 11 6 12 -1 1 4 11 6 12 -1 1 5 14 7 14.5 -0.5 0.25 5 14 6 12 2 4 5 14 7 14.5 -0.5 0.25 6 17 8 18 -1 1 6 17 8 18 -1 1 6 17 8 18 -1 1 7 20 9 21 -1 1 7 20 8 18 2 4 7 20 8 18 2 4 TOTAL: 0 60


42

Spearman rank correlation coefficient,

rs = 1 – 6(sum of 4.2 vvalues) n(n2 – 1) n = number of samples Substituting my results into the equation,

rs = 1 — 6 x 60 21(212 – 1)

= 0.961 The critical value for the Spearman Rank correlation coefficient at the p=0.05 level is 0.450 when n = 20 and 0.428 when n = 22. The rs value from our results is equal to 0.961, which is greater than both of these critical values. Hence, we can accept that there is significant correlation between the age of pineapple and the increase in diameter of the clear area. Therefore, the null hypothesis is rejected. The fact that the rs value has a positive sign means that there is a significant positive correlation. This agrees with the scatter graph that was drawn. Conclusion: The results of the statistical test show that there is significant positive correlation between the age of pineapple and the rate of increase in diameter of the clear area, as a result of digestion. Therefore, it can be said that as the age of pineapple increases, the rate at which digestion occurs is faster. This can be explained due to the fact that as the age of the pineapple increases the concentration of the enzyme stem-bromelain, which is responsible for digestion, increases. This is because more enzyme molecules are produced as the pineapple matures. Enzymes work by having a cleft in their surface to which complementary-shaped substrate molecules can bind. As the concentration of the enzyme increases, there are more active sites available that substrate molecules can bind to. Hence, the number of enzyme-substrate complexes formed in a given time is greatly increased. The enzyme-substrate complex then breaks up to form the unchanged enzyme and the products. In the case of this experiment the protein, gelatine, is broken down by the enzyme stem-bromelain to form products, one of which is water. As the rate at which the enzyme works is increased, the amount of gelatine that is broken down into water is increased, and the diameter of the clear liquid area enlarged. However, this is only true up to a certain point. According to the scattergraph drawn, after 7 days the correlation between the 2 variables is no longer obvious. It seems as if the position of the points begins to drop or steady out. This could be explained as after a certain amount of time, all of the enzyme that could be produced has been produced, and so the concentration of the enzyme can increase no further. Furthermore, it could be that as the pineapple gets old it might become mouldy and the enzyme may be destroyed. However, further work would be needed to understand the true cause of this. In conclusion, it can be seen that up to a certain extent, as the age of pineapple increases, the concentration of the enzyme stem-bromelain increases. Consequently, the rate at which the enzyme works is increased. This agrees with the hypothesis, and answers the initial aim of the experiment. Evaluation: Using the results, a conclusion was drawn which answered the questions that were posed in the aims of the experiment. Hence, the experiment can be seen as a success. Furthermore,


43

the results of the experiment and of the statistical test agree with my background knowledge. Despite this, there were a few limitations to the experiment. • A fridge was used to maintain a constant temperature, maintaining a fair test.

However, enzyme activity is also dependent on temperature, and the temperature of the fridge was too cold for the enzymes to work at their optimum rate. The result of this was that the increase in diameter of the clear area was a relatively small number. To improve this, the thermostat on the fridge could have been set to a higher temperature.

• The method of cutting wells in the gelatine posed the problem that the pineapple juice could seep underneath the gelatine. Hence, the enzyme in the juice would have reached further parts of the plate and may have meant that the enzyme digested a larger area of the protein than normal.

• The method of filling the wells with pineapple juice also meant that the volume of juice was not always constant. This is because it was hard to judge whether the level of the juice was the same every time. To prevent this, a trial experiment would have been carried out to see how much juice the well would hold. This amount of juice could then be added to the well using a pipette. Hence, a constant volume would have been maintained.

• When measuring the diameter of the clear liquid area, it was often hard to match up the edge of the liquid area to the graduations on the ruler. To improve this, graph paper could have been used instead of a ruler to measure the diameter.

If the experiment was to be carried out again these improvements would be included, improving the quality of the results. Furthermore, the experiment would have been repeated many more times. This would have helped to eliminate any anomalies and provide more accurate results. Further work would also include carrying out the experiment for a longer amount of time. This would help us to understand the pattern of the graph if the age of the pineapple was increased even more, for example did the rate of digestion begin to drop or steady out? This would fill in the gaps from the conclusion and give a wider picture of the relationship between the dependent and independent variables. In addition, future work could involve investigating the other variables such as temperature, to see how they affect the rate at which the enzyme works.

Commentary

I(a) The statistical test is correct and directly linked to the hypothesis. It is well set out and clearly explained in the student’s own words. This could easily meet the requirements for a maximum mark but the data is simply a diameter when the pattern shown by area digested might be different and more meaningful. I(a) Towards the upper end of the 4–6 range.

I(b) There is a basic enzyme explanation for the data. References to ‘rate’ are not accurate. The main trend shown is recognised and some very basic suggestion as to its cause is made. I(b) This only just reaches the 4-6 range.

I(c) The analysis of the method reveals a catalogue of very poor planning and would have been better in that section They are certainly the main flaws in this but only limited credit is given because a much better technique of assessing bromelain activity is needed if these flaws are to be overcome. Attempts to suggest other modifications are naïve — increase the temperature of the fridge. I(c) 4-6.

Overall I = 4 I(b) is too weak to justify any intermediate marks here.


44


Exemplar 3

Investigating contrast sensitivity in human eyesight Statistics: I will use a Mann Whitney U Test to demonstrate the data statistically. (Calculations in appendices). The following table shows the lowest line read for all the subjects on each chart, and the medians. Line on eye chart 0 1 2 3 4 5 6 7 8 9 10 Median High-contrast chart: Number of people 0 0 0 0 1 3 1 1 0 3 21 Line 9

Low-contrast chart: Number of people 1 2 0 2 3 4 10 7 1 0 0 Line 6

Experimental hypothesis: The greater the contrast between letters and their background, the more letters read on the eye chart. Null Hypothesis: There will be no difference in the amount of letters read on a high-contrast eye chart and a low-contrast chart. The lowest value between U1 and U2 is U2, which = 2.5. Also: n1 = 11 n2 = 11 Using a Mann Whitney U table, the critical value at 5% probability is 30. 2.5 (U1) is lower than the critical value of 30, therefore the null hypothesis is rejected and the experimental hypothesis is accepted. More lines can be read on the high-contrast charts than the low-contrast charts. Data Analysis: The result of the Mann Whitney U Test showed that eyesight is worse in low-contrast than high-contrast conditions. This is because at the 5% probability level, the value of U1 (2.5) was far lower than the critical value of 30. Therefore there is less than a 5% probability that the results occurred due to chance, and more than a 95% chance that the results are significantly different. This agrees with the experimental hypothesis that the greater the contrast between letters and their background, the more letters read on the eye chart. Graph 1 clearly shows us that most people can read up to line 10 (21 out of 30 subjects) and the data is close together. This is because there is high-contrast between the black letters and the white background and because most of the subjects had normal vision. Graph 2 shows us that in low-contrast conditions, the furthest read is line 8. The grey letters on the second chart have a high spatial frequency. This means that the alternating light and dark bars in a sine wave grating are narrow [Appendix 3].


45

Contrast Sensitivity Function

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 10 20 30 40 50 60

Frequency [cycles/degree]

CSF

Valu

e

Low spatial frequency (wide bars) High spatial frequency (narrow bars) [Appendix 4]

Images from the external world are taken in by neural retinal cells in the eye, which convert light energy into neural signals. These neural signals are then transmitted to the brain [Appendix 5]. The brain cannot distinguish patterns with very high frequencies (above 60 cycles/degree) due to the number of photoreceptor cells, which is a limiting factor [Appendix 6]. The contrast sensitivity function (sensitivity to different spatial frequencies) peaks at a value of 1 when the spatial frequency is 8 degrees/cycle. Above this value, then the higher the spatial frequency, the lower the contrast sensitivity function. The following graph shows the contrast sensitivity function.

[Appendix 6]


46

The grey letters have a high spatial frequency so the contrast sensitivity function is lower, so fewer letters can be read on the chart. This shows that driving would be more dangerous in low-contrast than high-contrast situations. The data is far more spread out for the low-contrast chart. Those that could not read far on the high-contrast chart could read even less, or not at all, on the low-contrast chart. Graph 3 shows us that even though the participants could all read up to line 10 on the first chart, they were differentiated on the low-contrast chart. The subjects’ vision on the low-contrast chart was spread over 4 lines on the chart, which is a significant difference, considering they could all read the same line on the high-contrast chart. This highlights the differences in eyesight between individuals and the impact low-contrast has on our vision. From the data collected, the overall patterns for males and females correspond. Gender, therefore, has no effect on eyesight. Evaluation: The time taken to read each eye chart was uncontrolled. This could have introduced random errors because after staring at an object for long enough your eyes become accustomed and focus slowly on it. People may have squinted to see further than when their eyes are relaxed. Also, the letters may have been blurry, which does not truly reflect the person’s vision. Error bars are not needed on the graphs because each person is individual and consequently the mean and standard deviations are irrelevant calculations. However, a large sample of 30 subjects was taken, giving representative data which reduced the likelihood of inconsistent results, such as those people with shortsightedness. Uncontrolled variables were kept to a minimum to reduce error. The degree of error for this investigation was quite low and consequently the data was significantly different. The distance from the eye chart was kept constant because eyesight worsens with distance due to elongation of the lens to focus light rays on the retina [Appendix 7]. Age was kept constant because diseases that affect vision such as glaucoma and cataracts are common in older people. Position of the charts and lighting were also kept constant. Measurements taken were repeatable because the experimental procedure was short and simple. The large sample, gave enough replicates to support the conclusion (ignoring anomalies). Therefore, the results are reliable because it was controlled, with a low degree of error, and repeatable. However, I was only able to compare two different contrasts, which were extremes. I could not tell if contrast levels in between had the same effect or how much they affected eyesight. This investigation only looked at letters on a white background, so other colours of background may have a different effect. I could modify the experiment by varying the background of the eye chart rather than the shade of the letters because this would be a more accurate representation of nighttime vision. The eye chart for low-contrast could instead have black letters printed on a grey background.


47

Commentary

I(a) The statistical test is well chosen for this data which does not always show a normal distribution. It is explained well and is clearly understood but would have been improved by the inclusion of at least one stage such as ranking in the calculation. I(a) 7–9 not max.

I(b) There is some complex theory quoted but it is well-selected and there is a clear link to each of the sources used and how this is applied to the actual data. It is concise and well-written. I(b) 7–9 Good.

I(c) Certainly the conclusions are supported by the data. The evaluation and suggestions for modifications would benefit from a more extensive analysis and some comments are a little superficial. I(c) At the top end of the 4–6 range, possibly 7-9.

Overall I = 6/7.

Tuto

r su

ppor

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ials

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) —

Issu

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— N

ovem

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2008

© E

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ed 2

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48

Com

mun

icat

ing

Ass

essm

ent

crit

eria

Le

vel o

f re

spon

se

a)

focu

ses

on t

he o

rgan

isat

ion

of t

he r

epor

t as

a s

cien

tifi

c re

cord

of

the

inve

stig

atio

n.

b)

focu

ses

on t

he a

bilit

y of

the

stu

dent

to

sele

ct t

he m

ost

appr

opri

ate

form

of

grap

hica

l pre

sent

atio

n th

at is

wel

l-m

atch

ed t

o th

eir

hypo

thes

is a

nd is

pre

sent

ed a

ccur

atel

y.

c)

focu

ses

on t

he a

ccur

acy

of t

he w

ritt

en r

epor

t an

d th

e co

rrec

t lis

ting

of

sour

ces

in a

bib

liogr

aphy

.

d)

focu

ses

on t

he r

ange

of

sour

ces

used

and

an

eval

uati

on o

f th

eir

scie

ntif

ic c

redi

bilit

y.

Mar

k ra

nge

Com

mun

icat

ing

a)

The

layo

ut o

f th

e pa

per

larg

ely

conf

orm

s to

tha

t ex

pect

ed o

f a

scie

ntif

ic p

aper

. Th

e or

gani

sati

on o

f th

e re

port

sh

ows

evid

ence

of

som

e th

ough

t an

d th

e ai

m o

f th

e in

vest

igat

ion

is s

tate

d. Im

ages

, w

hen

used

, ar

e re

leva

nt t

o th

e po

ints

mad

e.

b)

Dat

a is

pre

sent

ed in

gra

phs,

tab

les

or d

iagr

ams,

whi

ch a

re m

ostl

y ap

prop

riat

e an

d fo

llow

sci

enti

fic

conv

enti

ons

for

pres

enta

tion

.

c)

Spel

ling,

pun

ctua

tion

and

gra

mm

ar a

re g

ener

ally

cor

rect

, so

me

tech

nica

l ter

ms

are

used

app

ropr

iate

ly a

nd m

ost

sour

ces

used

are

ack

now

ledg

ed in

a b

iblio

grap

hy.

d)

Sour

ces

incl

ude

at le

ast

one

prof

essi

onal

sci

enti

fic

jour

nal.

At

this

lev

el t

here

wil

l be

som

e ba

sic

orga

nisa

tion

of

the

repo

rt i

nto

clea

r se

ctio

ns.

Dat

a w

ill

be p

rese

nted

in

a su

itab

le f

orm

at w

hich

aid

s an

alys

is b

ut t

his

may

be

lim

ited

or

of u

nsui

tabl

e fo

rmat

.

Ther

e is

lim

ited

tec

hnic

al l

angu

age

and

som

e sp

elli

ng e

rror

s or

poo

r gr

amm

atic

al e

xpre

ssio

n w

hich

can

con

fuse

the

un

derl

ying

mea

ning

. So

urce

s ar

e ve

ry l

imit

ed a

nd l

iste

d in

a f

orm

at w

hich

doe

s no

t id

enti

fy t

hem

acc

urat

ely.

The

term

‘pr

ofes

sion

al s

cien

tifi

c jo

urna

l’ w

ill

be j

udge

d in

the

lig

ht o

f w

hat

coul

d re

ason

ably

be

acce

ssib

le t

o an

A L

evel

st

uden

t bu

t th

ere

are

man

y so

urce

s w

hich

are

fre

ely

avai

labl

e to

all

stu

dent

s. (

See

addi

tion

al n

otes

.)

0–2

mar

ks

Tuto

r su

ppor

t m

ater

ials

— E

dexc

el G

CE in

Bio

logy

— S

uppo

rt b

ookl

et f

or U

nit

6 (6

BI06

) —

Is

sue

1 —

Nov

embe

r 20

08 ©

Ede

xcel

Lim

ited

200

8

49

a)

Th

e la

yout

of

the

repo

rt m

ostl

y co

nfor

ms

to t

hat

expe

cted

of

a sc

ient

ific

pap

er w

ith

subh

eadi

ngs

used

eff

ecti

vely

. Th

e ai

m(s

) an

d co

nclu

sion

(s)

of t

he in

vest

igat

ion

are

stat

ed.

Imag

es,

whe

n us

ed,

illus

trat

e po

ints

cle

arly

.

b)

Dat

a is

pre

sent

ed in

wel

l cho

sen

grap

hs,

tabl

es o

r di

agra

ms,

whi

ch u

sual

ly f

ollo

w s

cien

tifi

c co

nven

tion

s an

d m

ostl

y us

e SI

uni

ts,

whe

re a

ppro

pria

te,

corr

ectl

y.

c)

Spel

ling

punc

tuat

ion

and

gram

mar

are

cor

rect

, ap

prop

riat

e te

chni

cal t

erm

s ar

e us

ed t

hrou

ghou

t. S

ourc

es a

re

sele

cted

and

use

d ap

prop

riat

ely

and

are

corr

ectl

y re

fere

nced

wit

hin

a pr

oper

ly c

onst

ruct

ed b

iblio

grap

hy.

d)

Ther

e is

som

e di

scus

sion

of

the

cred

ibili

ty o

f so

urce

s us

ed.

To r

each

thi

s le

vel

it i

s es

sent

ial

that

the

rep

ort

is w

ell-

stru

ctur

ed a

nd i

t is

lik

ely

that

the

aim

(s)

and

a su

mm

ary

of

conc

lusi

ons

wil

l be

inc

lude

d in

a c

onci

se a

bstr

act.

Any

im

ages

sho

uld

be c

lear

ly l

abel

led

and

if t

hey

are

not

refe

rred

to

in

the

repo

rt i

t w

ill

be d

iffi

cult

to

judg

e w

hich

poi

nts

they

ill

ustr

ate

At

this

lev

el s

ome

form

of

grap

hica

l pr

esen

tati

on w

ould

nor

mal

ly b

e ex

pect

ed.

The

grap

hica

l fo

rmat

wou

ld b

e ap

prop

riat

e to

the

dat

a an

d us

eful

in

anal

ysin

g th

e da

ta w

ith

resp

ect

to t

he h

ypot

hesi

s. A

ny m

anip

ulat

ed d

ata

used

to

cons

truc

t su

ch g

raph

s w

ill

be c

lear

ly t

abul

ated

.

Ther

e w

ill

be v

ery

few

typ

ogra

phic

al e

rror

s al

thou

gh a

n in

abil

ity

to s

pell

sci

enti

fic

term

s or

cor

rect

nam

es o

f or

gani

sms

unde

r in

vest

igat

ion

is w

eak

for

this

lev

el.

The

repo

rt w

ill

be e

asy

to r

ead

and

unde

rsta

nd.

All

ref

eren

ces

quot

ed s

houl

d be

acc

urat

ely

iden

tifi

ed s

o th

at i

t is

eas

y fo

r th

e re

ader

to

gain

acc

ess

to t

he a

ctua

l ar

ticl

e,

pape

r or

web

pag

e. It

sho

uld

be c

lear

whe

re i

n th

e re

port

the

sou

rces

quo

ted

have

bee

n us

ed.

It i

s ho

ped

stud

ents

wil

l us

e sk

ills

gai

ned

at A

S le

vel

to d

iscu

ss t

he c

redi

bili

ty o

f so

me

of t

heir

sou

rces

.

3-4

mar

ks

Tuto

r su

ppor

t m

ater

ials

— E

dexc

el G

CE in

Bio

logy

— S

uppo

rt b

ookl

et f

or U

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6 (6

BI06

) —

Issu

e 1

— N

ovem

ber

2008

© E

dexc

el L

imit

ed 2

008

50

a)

Th

e la

yout

of

the

repo

rt c

onfo

rms

to t

hat

expe

cted

of

a sc

ient

ific

pap

er w

ith

appr

opri

ate

and

help

ful s

ubhe

adin

gs.

The

orga

nisa

tion

of

the

repo

rt s

how

s ev

iden

ce o

f th

ough

tful

pla

nnin

g an

d ai

m(s

) an

d co

nclu

sion

(s)

of t

he p

roje

ct

are

clea

rly

stat

ed a

nd d

iscu

ssed

. Im

ages

illu

stra

te t

he p

oint

s ef

fect

ivel

y an

d en

hanc

e th

e cl

arit

y of

the

rep

ort.

b)

Dat

a is

pre

sent

ed e

ffec

tive

ly in

gra

phs,

tab

les

or d

iagr

ams

that

fol

low

sci

enti

fic

conv

enti

ons

and

are

clea

rly

and

accu

rate

ly la

belle

d us

ing

SI u

nits

whe

re a

ppro

pria

te.

c)

Spel

ling,

pun

ctua

tion

and

gra

mm

ar a

re c

orre

ct,

and

appr

opri

ate

tech

nica

l ter

ms

are

used

thr

ough

out.

d)

Sour

ces

used

are

eva

luat

ed w

ith

refe

renc

e to

the

ir c

redi

bilit

y w

ithi

n th

e w

ider

sci

enti

fic

com

mun

ity.

The

repo

rt a

t th

is l

evel

wou

ld b

e ex

pect

ed t

o be

con

cise

and

ver

y w

ell-

orga

nise

d. T

here

wou

ld b

e a

shor

t ab

stra

ct

sum

mar

isin

g th

e m

ain

feat

ures

inc

ludi

ng t

he c

oncl

usio

n(s)

.

Gra

phic

al p

rese

ntat

ion

mus

t be

sel

ecti

ve w

ith

a sm

all

num

ber

of g

raph

s to

ill

ustr

ate

impo

rtan

t tr

ends

and

pat

tern

s on

th

e co

rrec

t fo

rmat

. Th

ey w

ill

be a

ccur

atel

y la

bell

ed a

nd c

aref

ully

plo

tted

.

Ther

e w

ill

be v

ery

few

min

or s

pell

ing

erro

rs a

nd a

ll s

cien

tifi

c or

tec

hnic

al t

erm

s w

ill

be c

orre

ct.

All

quo

ted

sour

ces

wil

l ha

ve s

ome

com

men

t as

to

thei

r cr

edib

ilit

y as

acc

epta

ble

scie

ntif

ic k

now

ledg

e.

5–6

mar

ks


51

Notes on Graphical Presentation

The selection of correct graphical format is a key element in communicating. The graph is meant to be a pictorial representation of the main trends and patterns in the data bearing in mind the suggested hypothesis. This can in some circumstances also lead to a determination of a mathematical relationship or rate calculations.

Many students find this difficult. The two main areas of difficulty are:

(i) Selecting the format, which is appropriate.

(ii) Distinguishing correctly between line graphs, histograms and bar charts.

(iii) Restricting the number of graphs to those, which are key to the analysis of the hypothesis. In this respect it is common to see repetitive graphs of raw data but not the all-important summary graph, eg graphs of raw data for a set of readings at individual temperatures but no graph of overall rate vs. temperature.

a. Drawing graphs

The examiners or moderators will show no preference for either computer drawn graphs or for hand drawn alternatives although hand drawn graphs will have to be scanned into the final document for submission. Students drawing graphs by hand will need to include all the elements below and use a thin pencil or pen to draw lines. Those choosing to use computer programmes must have the relevant knowledge to be able to produce a good graph.

It is the quality, relevance and accuracy of the graph that counts, no matter how it is drawn. Hence, axis labels with units, suitable scales, clear accurately plotted points and appropriate lines are common to both.

It is not a requirement that students draw lines of ‘best fit’ on their graphs. In fact, in many cases this is scientifically poor practice where there is no reasonable assumption that this is the relationship between the variables.

Where there is a continuous variable on the horizontal axis and no simple relationship we suggest that line graphs are drawn point to point with a straight line.

When presenting data where a correlation is investigated, scattergraphs of plotted points are often better left without a straight line, which has been arbitrarily selected, then analysed using a correlation test. More able students may wish to calculate the equation of the straight line using ANOVA but this is not a requirement at this level.


52

Communicating

Exemplar 1

The effect of position on the rocky shore on the number of grey top shells

Graph to show changes in the number of grey top shells at distances from the sea wall in transects 1-5

02468

1012141618

0 5 10 15 20 25 30 35 40 45 50Distance (M)

No.

Top

shel

ls

Transect 1

Transect 2

Transect 3

Transect 4

Transect 5

Graph to show differences in temperature in the five transects

0

5

10

15

20

25

0 5 10 15 20 25 30 35 40 45 50Distance from sea wall (M)

Tem

pera

ture

(deg

rees

C)

Transect 1Transect 2Transect 3Transect 4Transect 5


53

Commentary

C(a) This report was generally well-organised with use of sub-headings and a logical presentation. There was an abstract and some illustrations (not shown in these extracts) which were relevant. C(a) 5-6.

C(b) Graphical presentation is poor. A scattergraph might be expected for a correlation and at least some summary data calculated to show the overall trend. The graphs have been compressed to fit all on one page and this detracts from their clarity. The two abiotic graphs simply plot raw data and are not directly linked to the hypothesis. C(b) 0-2.

C(c) Sources are included (see sect R) but there is no attempt to comment on their validity. C(c) 0-2.

Overall C = 2.

Graph to show changes in light intensity in the five transects

0

5000

10000

15000

20000

25000

0 5 10 15 20 25 30 35 40 45 50Distance from sea wall (M)

light

inte

nsity

(lux

)

Transect 1Transect 2Transect 3Transect 4 Transect 5


54

Communicating

Exemplar 2

Investigating the effect of ageing on bromelain activity in pineapple

Diameter of cleared area against age of pineapple

0

1

2

3

4

5

6

7

8

9

10

0 2 4 6 8 10 12

Age (days)

Dia

m o

f wel

l (m

m)

www.greatvistachemicals.com/biochemicals/bromelain.html Date: October 2004 www.thorne.com/altmedrev/fulltext/bromealin1-4.html Date: October 2004 http://www.zooscape.com/cgi-bin/maitred/GreenCanyon/questp415668/jornad1.25866175 Date: October 2004 www.edexcel.com/VirtualContent/24971.pdf Date: October 2004 Author: Salters Nuffield Advanced Biology Date: 2002 Title: AS Student book 1 Page: 77 Author: Salters Advanced Chemistry Date: 2000


55

Title: Chemical Storylines Page: 160 Author: John Adds, Erica Larkcom, Ruth Miller, Robin Sutton Date: 3/2000 Title: Tools, Techniques and Assessment in Biology. A course Guide for Students and Teachers Page:117-118 I have tried to use a range of resources. My A Level textbooks are reliable sources because they are well known and sold nationally. Edexcel is an examining board and would check all the information on its site. The others are companies who sell chemicals so have experts with good knowledge.

Commentary

C(a) The report is very well organised with clear sections with headings which reflect a logical, scientific approach.

There was some illustration (omitted here) of the measurement of diameters, which was relevant and useful. C(a) 5-6.

C(b) The data is correctly presented as a well-formatted scattergram. C(b) 5-6.

C(c) There is appropriate vocabulary and use of language. Sources are limited but clearly listed in a separate bibliography. C(c) 3-4.

C(d) There is some attempt to discuss sources but at a very simple level. Source (ii) might be considered a journal but it is very marginal. C(d) 2/3.

Overall C = 3


56

Communicating

Exemplar 3

Investigating contrast sensitivity in human eyesight

Results

Results for high-contrast eye chart



0 0 0 1 0 0 2 0 0 3 0 0 4 1 0 5 0 3 6 1 0 7 0 1 8 0 0 9 2 1 10 11 10

Total 15 15

Results for low-contrast eye chart

Lowest line read on eye chart

Number of Males Number of Females

0 1 0 1 1 1 2 0 0 3 0 2 4 1 2 5 2 2 6 6 4 7 4 3 8 0 1 9 0 0 10 0 0

Total 15 15


57

Lowest line read on high-contrast chart

0

2

4

6

8

10

12

0

2

4

6

8

10

12

0 1 2 3 4 5 6 7 8 9 10

Num

ber o

f peo

ple

Lowest line read on chart


Lowest line read in low-contrast chart

0

1

2

3

4

5

6

0

1

2

3

4

5

6

0 1 2 3 4 5 6 7 8 9 10

Num

ber o

f peo

ple




58

The following graph eliminates all participants unable to read the 10th line on the high-contrast chart. There are 21 subjects’ data incorporated into this graph for the low-contrast chart.

Low-contrast vision in the well-sighted

0

1

2

3

4

5

6

0

1

2

3

4

5

6

5 6 7 8

Num

ber o

f peo

ple


Number of males Number of females

Appendices Appendix 1: www.contrastsensitivity.net — Date accessed: 25/08/04 Appendix 2: ‘Eye Health’ by Sandra Salmans Appendix 3: www.cquest.utoronto.ca/psych/psy280f/ch5/sf.html Appendix 4: www.cquest.toronto.edu/psych/psy316s/patternGif/frequency.gif — Date accessed: 31/10/04 Appendix 5: www.lighthouse.org/research_spatial.htm — Date accessed: 31/10/04 Appendix 6: www.cg.tuwien.ac.at/research/these/matkovic/node20.html — Date accessed: 31-30-04 Appendix 7: Biological Sciences Review — Janet Marsden I have selected a range of sources to use in my research. Sources 2, 3 and 6 are from internationally known universities (Toronto and Vienna). Source 6 is taken from a pHD thesis which has been supervised by a senior member of the university and then checked like an examination paper before the higher degree was awarded so has a high level of scientific credibility. Source 1 is slightly different as this is a website of a commercial company, Vision Science Research Corporation based in the USA. It carries out research in the area of sight testing and sells machines for testing for various eye conditions. It does need to sell these machines to doctors and hospitals so must have some good scientific information to do this.


59

Biological Sciences Review is written by well-known experts in their field and gives their scientific background as well as links to other academic references. This can also be regarded as a reliable source. My other source of written information (2) is a published text book which again will have been reviewed and if it is published there will be checks on the author and the information.

Commentary

C(a) This report was concise clearly laid out with excellent section headings. There were some good illustrations in section I. C(a) 5–6.

C(b) The graphs are clear and analyse interesting aspects of the hypothesis. The use of 3D columns is visually effective but scientifically detracts from the accuracy and ease of interpretation. There could be debate about whether the horizontal axis is continuous and hence the format should be a histogram or a bar chart, as shown is more appropriate as these are discrete measurements but overall this was accepted. C(b) 5–6.

C(c) All spelling punctuation and grammar was good with good use of technical terms. Sources are correctly applied and clearly listed. C(c) 5–6.

C(d) There is sensible discussion of the credibility of sources. C(d) 5–6.

Overall C=6 There is no reason not to award a maximum here.


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Summary marks for the exemplar investigations

Note

All marks suggested for these exemplars should be regarded as indicative only. Decisions on final standards to be applied and grade boundaries can only be reached after careful inspection of actual students’ work by a team of experienced examiners and moderators.

Exemplar 1

The effect of position on the rocky shore on the number of grey top shells.

R = 7, P = 1, O = 6, I = 3, C = 2 TOTAL = 19 marks

Exemplar 2

Investigating the effect of ageing on bromelain activity in pineapple.

R = 3, P = 6, O = 4, I = 4, C = 3 TOTAL = 20 marks

Exemplar 3

Investigating contrast sensitivity in human eyesight.

R = 9/10, P = 9, O = 6, I = 6/7, C = 6 TOTAL = 37 marks

Note: in calculating this total the higher mark was awarded for R but the lower mark for I.

Indicative grades

Whilst exemplars 1 and 2 have similar totals which might be expected to correspond to low grades, they do illustrate a wide range of marks in each criterion.

Exemplar 3 is of a high grade piece of work.


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Offering students individual opportunities to meet all the criteria

a. Generating a variety of suitable investigations.

First of all it is worth repeating the general advice given in planning notes.

(i) Ensure that students investigate a meaningful but interesting question and do not attempt simply to demonstrate a basic ‘fact’. However, it is recognised that many interesting ideas are used year on year by centres. In most of these cases the questions may be familiar to teachers but not to each cohort of students and therefore they still provide excellent opportunities.

(ii) Ensure that the hypotheses to be tested are well-focused and do not attempt to investigate multiple variables. The inclusion of a clear statistical intent in the hypothesis is an excellent way of ensuring the hypothesis is clear. Such statements as ‘There is a significant difference between …..’ or ‘There is a significant correlation between ..…’ provide a clear focus for theoretical background and planning data collection etc.

When planning ahead it is vital to be able to offer a variety of investigations which will allow students to address the criteria in different ways. Clearly what is offered will depend upon your resources, your freedom to take students on visits and the numbers in each cohort.

Whatever is planned it is vital to review your ideas by asking the following question. ‘Will the investigations on offer lead to most students using almost identical methodology, data analysis and evaluation?’ If the answer to this question is yes then an examiner or moderator will be placed in a difficult position in attempting to determine the individual contribution of each student and find it more difficult to support the award of high marks. Using a simple matrix can often generate a surprising number of individual variants. The one shown below uses field work on a rocky shore as an example.

Organism Size/ratios verses position on shore

Associations Morphology verses aspect/ exposure

Littorina obtusata

Dogwhelks

Limpets Fucus vesiculosus

Fucus serratus

Ascophyllum nodosum

Lichens


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The type of hypotheses derived from such a matrix could then be:

Significant differences

1. Height to base ratio of limpets.

2. Numbers of paired bladders of F. vesiculosus at two different heights on the shore or different exposures.

3. Operculum to length ratio of dogwhelks.

4. Abundance of the orange lichen Caloplaca sp. on exposed and sheltered shores.

Significant correlations

1. Colonisation of F. serratus by the spiral worm Spirorbis sp. at different heights of the shore.

2. Desiccation rates of different algal species compared to their position on the shore.

3. Abundance of the epiphyte Polysiphonia with age of Ascophyllum nodosum.

Significant associations

1. Colour morphs of Littorina obtusata on different algal species.

These are only a few examples of what might be investigated on such a rich habitat but they do illustrate a wide range of approaches.

A simple way to create even more variation would be to direct students towards a certain approach.

A number of the examples above could be approached in two different ways such as investigating a significant correlation or a significant difference in algal desiccation by sampling a range of algae or just an upper and a lower shore alga. Hence whilst the basic concept is similar there will be very different reports as sampling, data presentation and statistics will provide plenty of individual variation.

Provided that there is a number of alternatives on offer it is also possible to draw up a similar number of variations for laboratory-based investigations.

In Appendix 1, there are some suggestions for a range of investigations not commonly attempted.

b. Working with larger groups

Many centres will have large cohorts of A2 students. It is unlikely, even with a great deal of imagination, that sufficient numbers of different investigations can be identified. In such cases it is acceptable for there to be several examples of similar investigations. A sensible approach to this problem would be to treat each teaching group separately. A good range of different investigations would be expected within this group but the process could then be repeated with each different group.

In these circumstances it would be advisable to include, with the work, a short note explaining to the examiner or moderator how the groups have been organised within the centre.

This is particularly important for samples submitted for moderation, which are randomly selected and therefore may not contain a representative proportion of each investigation.


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c. A2 level of investigation

There are two aspects to consider when making a judgement about whether the investigation is of the correct level.

(i) Is the level of accuracy of measurement sufficient to produce reliable data?

(ii) Is the biological knowledge and understanding required of A2 level?

A good example might be to consider a simple investigation into apple browning.

Simply attempting to assess apple browning subjectively or against a standard scale would not be sufficient at this level for (i). Even measuring area is badly flawed as there is no quantitative link to why one area should brown and not another. If this was simply used to compare one apple with another it would not meet the requirements for (ii) either.

However if apple samples were filtered or centrifuged then tested in a colorimeter, some accurate data could be obtained. This would still be insufficient unless it were linked to an interesting and more challenging question. In this case it could be used to look at why some apple varieties brown much more quickly than others. Is this because of the presence of polyphenol oxidase inhibitors, simply a lack of the enzyme or something else? What predictions could be made in each of these cases and how could they be tested? Obviously there is now the opportunity for some individual research, thinking and perhaps a little ingenuity.

This would also serve to illustrate that it is not the use of sophisticated apparatus that counts but the formation of interesting and informed questions that is more likely to yield successful investigations. As biologists at this level we are in a unique position to pose such interesting questions and investigate them in a meaningful manner.

d. A word of caution

Perhaps as a legacy of Key stage 3 and previous GCSE coursework, there is an ongoing reluctance to move away from standard enzyme investigations. It should be noted that merely repeating such investigations at this level will not show the necessary progression for the award of more than average marks.

If enzyme investigations are to be used students should be aware that the examiners or moderators will be looking for a much higher degree of understanding and measurement of rates and more sophisticated hypotheses than those commonly displayed at lower mark levels.

On a similar level, human investigations with extremely poorly controlled sampling or investigating simplistic changes in pulse rate, are unlikely to yield sufficient evidence for higher marks in several of the criteria.


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Giving help and assistance

All internal assessment depends upon the professional integrity of teachers. When submitting work for this examination you are asked to add your signature and declare ‘that the work of this student is, to the best of my knowledge, the student’s own’.

In simple terms this means that everything submitted for assessment must represent the best efforts of the student to address the criteria. Therefore any part of the report, which is not the direct result of their own thinking and is simply following the instructions of others must be annotated and not used in the final assessment. This could best be amplified in two stages.

a. Getting Started

All students will need considerable help and support to set them on the right path. In addition to having some prior knowledge of the techniques they are to use they may also require some assistance in finding relevant sources of information.

What is acceptable and desirable (i) The provision of simple ‘briefs’, where necessary, to provide important information that students would not be expected to know. This may include details of using a particular piece of apparatus they may not have met before or an outline introduction to a technique with which they are not familiar.

(ii) A check must be made on the initial outline plan to ensure that any obvious health and safety issues have been addressed and that the proposed methods are likely to yield meaningful data. Responses should point out the problem not the solution and provide an opportunity for the student to continue with an acceptable investigation. Where weak students are unable to formulate a plan that will enable them to proceed to the data collection stage in a meaningful way, then teachers should intervene with more detailed assistance with the award of a lower mark. In this way such students will at least be able to access higher marks in subsequent criteria rather than continuing with a poor plan.

What is not acceptable

(i) The provision of detailed ‘recipes’, which not only give essential information but also include detailed precautions or methods for controlling important variables. This is likely to prevent the student scoring more than minimal planning marks and to remove one of the main aims of trial testing, both of which are important criteria.

(ii) Responding to initial plans in such a way that the student is given many details, which might subsequently be credited as their own work.

b. The final stages

The examiners wish to encourage students to give as much evidence as they can of their ability to meet the criteria. As the criteria are marked in hierarchical fashion it is particularly important that students have made at least some attempt to address them all.

A checklist is included in this guide as Appendix 2.


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What is acceptable and desirable

(i) Teachers will need to check the report and ensure that the student has attempted all the criteria. To do this students may need to be given a short deadline to attempt to rectify any omissions or significant oversights but this should not be a prolonged or repeated process. The checklist can be used by students or teachers for this purpose.

(ii) It is not expected that teachers will withdraw from the normal teaching process, simply that they will take care to ensure that the final report is truly representative of the student’s ability.

Hence the following might be suitable responses:

‘ Your planning is weak — you need to think more carefully about other variables and exactly what you are to measure’.

‘You have not addressed I(c) — use clear subheadings to make sure you cover all the criteria’.

What is not acceptable

(i) Completed reports must not be returned to students for continued redrafting and especially if accompanied by detailed comments, written or oral, on how they might be improved. This clearly falls outside the meaning of ‘the student’s own work’ and erodes the differential between the work of more and less able students.

The following are the type of responses, which would be giving detailed assistance. They should be noted on the report and a reduced mark awarded.

‘You have drawn a line graph when it should be a bar chart.’

‘You should calculate the area of the cleared area by using the average of several diameters because it is not circular.’

Plagiarism

Edexcel is likely to penalise any student that deliberately copies information and attempts to pass it off as original work of their own. Since 2006, Edexcel has been using new software to identify any potential cases of plagiarism.

However, schools could also follow the Joint Council for Qualifications(www.jcq.org.uk) advice on detecting plagiarism:

Keeping watch on content • Varying quality of content is one of the most obvious pointers. Well-written

passages containing detailed analyses of relevant facts alternating with poorly constructed and irrelevant linking passages ought to give rise to suspicion.

• Another practice is for candidates to write the introduction and conclusion to an assignment to make if fit the question, and then fill in the middle with work which has been lifted from elsewhere.

• If the work is not focused on the topic, but presents a well-argued account of a related matter, this could be a sign that it has been used elsewhere. The same applies if parts of the work do not fit well together in developing the response to the assignment.

• Dated expressions, and references to past events as being current can also be indications of work which has been copied from out-of-date sources.


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Keeping watch on vocabulary, spelling and punctuation • The use of a mixture of English and American vocabulary or spellings can be a

sign that the work is not original.

• If the piece contains specialised terminology, jargon, obscure or advance words, the internal assessors should ask if this is typical of this level of candidate and reasonable, or if it is because the candidate did not write the passage.

• Is the style of punctuation regular and consistent?

Keeping watch on style and tone • Look for differences in the style or tone of writing. If a candidate uses material

from textbooks alongside items from popular magazines the change of tone between the two should be marked.

• Look at level of sophistication of the sentence structure. Is this the sort of language that can be expected from a typical student? Is the use of language consistent, or does it vary? Does a change in style reflect a change in authorship at these points?

Keeping watch on presentation • Look at the presentation of the piece. If it is typed, are the size and style of font

uniform? What about use of headers and sub-headers? Are the margins consistent throughout? Does the text employ references and if so is the style of referencing consistent? Are there any references, for example, to figures, tables or footnotes, which don’t make sense (because they have not been copied)?

• Lack of references in a long, well-written section could indicate that it had been copied from an encyclopaedia or similar general knowledge source.

• Look out for quotations that run on beyond the part which has been acknowledged.

Other techniques • Type in phrases or paragraphs into ‘Google’ and see if this comes up with a

website that matches closely, if not entirely.

• Search parts of the bibliography for suspicious websites that are too closely matched to the title.

• Use free software as described on www.plagiarismdetect.com, www.turnitin.com, www.plagiarism.com, www.wordchecksystems.com or www.canexus.com/eve/index.shtml

Remember that the centre, as well as the student, is liable for any plagiarism because the teacher will have signed a declaration ensuring that the student’s work is their own.


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Appendix 1: Some ideas for investigation

Ideas can come from AS or A2 units or broadly associated biological principles. In practice, provided that the investigation is soundly based in A2 level biology, the examiners and moderators wish to encourage as wide a range of interesting ideas as possible.

However, centres are reminded that students are forbidden from submitting the same investigation for more than one subject. This will be particularly relevant for students who are also studying Psychology, Sports Science or Physical Education at Advanced level.

Plants

Further details of the ideas marked * can be found at the excellent Science and Plants for Schools website http://www-saps.plantsci.cam.ac.uk/ 1. *Pollen tube growth — is it affected by storage time? Sucrose concentration?

Excision of flower from stem?

2. Do conifer extracts inhibit growth/germination of other species?

3. *What is the effect of different growth substances on white mustard seed explants?

4. *Investigating photosynthesis — try interesting questions not just light intensity or wavelength, eg temperature or effects of other extracts/pollutants. Use different protocols see SAPS on immobilised algae using colorimetry or investigate the new carbon dioxide and oxygen sensors to measure rates.

5. *Using Duckweed as a bioassay.

6. How are stomatal numbers/sizes etc affected by growth conditions? Try direct observations of purple pigmented leaves of Tradescantia as well as nail-varnish peels (or less toxic water-based varnish*).

7. Stomata open in the light and close in the dark don’t they?

8. *Investigate the effects of ethene on sugar content of ripening fruits. (Ripening bananas provide ethene and Potassium Manganate IV will absorb it.)

Enzymes

A word of warning. Enzymes provide excellent material for investigations but experience has shown that many students submitting them find great difficulty in demonstrating any progression from modest GCSE standard. If you wish to use enzyme investigations please ensure that they have the potential to offer A2 level standards. Demonstrating denaturation or pH optima will qualify for very limited marks at this level. A good example of the standards expected is given in Unit 1 where the core practical asks for measurement of initial rates.

Enzymes become much more interesting when they are extracted by students and can be linked to interesting contexts.

9. *Catchecol oxidase can be extracted easily from mashed banana and used with pure catchechol to produce the same brown colour found in oxidising food and fruit.


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10. *Germinating beansprouts contain a phosphatase which shows end product inhibition in different phosphate solutions.

11. Potato extract contains a starch synthesising enzyme using glucose-1-phosphate as substrate (but this can be expensive).

Other enzyme ideas

12. Invertase is inhibited by high substrate concentrations.

13. Lowering temperature can increase the effective pH range of enzymes.

14. Can pH denaturation be reversed in immobilised enzymes?

BUT make sure you can measure RATE.

Human Investigations

More warnings. This type of investigation can provide good opportunities but also major pitfalls. It will be expected that some reasonable effort is made to standardise samples and quantify any variables such as ‘fit/unfit. Any measurements would also be expected to have sound validity.

15. Does cardio-vascular training reduce resting heart-rate?

16. How does colour/contrast affect eye-test results?

17. Does drinking caffeine really increase alertness/reaction time (NOT using dropped ruler test. Lots of accurate reaction timers available on-line). Be careful to distinguish reaction from reflex.

18. Given the switch in many school timetables is there any evidence that simple learning/reaction tests are better performed in the morning?

Respiration

Again avoid repeating well-documented ‘standard’ investigations.

Oxygen/CO2 sensors can be used to good effect with yeast cultures as well as oxygen evolved methods.

Methylene Blue and TTC are also alternatives for assessing rates but some standardisation of end point is vital.

19. Investigations can be linked to interesting questions on inhibitors.

If using different substrates ensure concentrations are SI molesdm-3 not %.

Fieldwork

Provides a very large range of opportunities for interesting and original work. Taking a large group to a single location using a similar technique might be very limiting but many locations offer a range of habitats. Once again try to get students to pose interesting questions.

An interesting way to increase variety is to guide students into different approaches to the same problem, eg do algae found on the lower shore desiccate more rapidly than those on the upper shore?


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Approaching this as a test for a difference between two selected species or as a correlation between several species moving down the sure ensures very different problems of sample selection, tabulation and graphical presentation and statistical analysis.

Investigations on individual species often offer more opportunities to meet the criteria to a high level.

20. Are colour morphs of Littorina mariae associated with different algal species?

21. Does the length of the first internode of Ammophila arenaria grow longer on more exposed dunes?

22. Does the distribution of one barnacle species vary with aspect of the rock?

23. Is the biodiversity in rock pools linked to times of immersion by the sea?

24. Is the distribution of Pleurococcus on the bark of trees influenced by aspect?

25. Is there a correlation between distribution of one plant species and soil water content?

26. Investigate factors affecting the decay of leaf litter.

27. Factors affecting the distribution/predation of holly leaf miners (see www.field-studies-council.org/outdoorscience/london/hampsteadheath/holly.htm).

28. Does trampling on a football/hockey field affect the distribution of Plantain sp. (Try quantifying trampling by direct observations of marked quadrats during sports sessions.)

29. Will global warming affect the development of tadpoles/ Brine shrimps (see www.ntlabs.co.uk). Note this is essentially a core practical and therefore students will need to demonstrate some originality of approach to achieve higher marks.

30. Do ant numbers increase around a sugar source by random accumulation or by communication?

31. Are there more earthworms in ‘organic’ soil?

Microbiology

Take care to ensure that alternatives offered give sufficient opportunity for individual planning, eg many students using bacterial lawns and simply testing different substances will result in lots of very similar reports making identical points or largely repeating their core practical training.

Consider methods such as optical density of liquid cultures too.

32. Investigating competition between two bacteria or fungi, etc.

These are just a few suggestions, there are obviously many more according to your location, ability to attend field centres and resources.


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Appendix 2: Unit 6 Individual Investigation — Checklist

Criterion

A2 level Biological knowledge used to explain the nature of the investigation.

All the information included is relevant to the hypothesis.

There is a good range of sources researched.


It is clear where in the report sources have been used.

Report has a clear plan of action and describes how all the main variables are to be controlled.

Which statistical test is to be applied is included in the plan.

Risk assessment is included.

A trial experiment has been carried out and simple results recorded.

Planning

Method has been amended in the light of trial experiment if necessary.

There is sufficient data to make some conclusions.

Tables have correct units in headings only and consistent use of sensible significant figures.


Readings are repeated if possible. Any significant anomalies are dealt with during data collection.

The table needed for the statistical test is included.

I have explained, in my own words, what the statistical test shows me about my hypothesis.

The main trends and patterns are described.

Researched information is used to try to explain the data that has been collected.

There is a discussion of the main limitations of the methods used.


Sensible modifications to the procedure have been suggested.


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Criterion

The report has been checked for spelling errors.

There are subheadings for each different section of the report.

The report has a word count on each page and is not longer than 3300 words.

The graphs are carefully selected to be useful in interpreting the data and making conclusions concerning the hypothesis.

Sources of information are accurately listed and include at least one professional scientific journal.

Communicating

There is a comment on each source describing its credibility.


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Appendix 3: Guidance for centres on electronic submission of candidates’ assessed work

What is a sample?

A sample is a representative selection of candidates’ completed work for a unit.

It is required that internal standardisation has been carried out within the centre prior to the submission of marks.

A sample must be submitted for each unit you have entered candidates in order to verify your assessment and to issue final marks to candidates.

How do I know which candidates’ folder to include in the sample?

Sampled candidates are identified with a tick on the Edexcel online mark submission screens.

How do I submit a sample?

Samples are submitted to the moderator on CD. You should submit one CD per unit, and keep a back up of all sampled work securely within your centre

How should I format the CD that is sent to the moderator?

Each student’s assessed work submitted to Edexcel should be in a single document; this final document must be in one of the following formats: • .rtf Rich Text Format

• .pdf Portable Document Format (Adobe Acrobat)

You must only submit the final version of work for each candidate which must be in a single document. If you are able to use Word to create your work then you should do so. It will be much simpler for you if you can use Word, because then your work is more likely to be compatible with other computers and it will also be easier to hand in.

If you do not have access to a PC with Word, then try to use an equivalent word processing programme. When the final document is complete it can then be saved as a Rich Text Format document or converted to a pdf file.

CDs which are not formatted, labelled or structured according to guidelines provided in this document will be returned to centres unmoderated. Under such circumstances, Edexcel cannot guarantee the timely issue of results for candidates entered. Candidates work must be burnt to CD. They should not be burnt to DVD.

Should I zip the work that I burn to CD?

Please do not zip folders containing candidate work. The moderator should be able to access all files and folders directly from the CD without unzipping or altering in any way the files or folder structure.


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How should candidates work be organised and named on the CD?

A separate folder on the top-most level of the folder tree should be used for each of the sample candidate’s work. Each folder should be named according to the following naming convention:

[centre #]_[candidate #]_[first two letters of surname]_[first letter of first name]

For example, John Smith with candidate number 9876 at centre 12345 would have work in a folder titled, ‘12345_9876_SM_J’

Do I need to include the Cover Sheets on the CD?

Yes. You should create a separate folder on the top-most level of the folder tree named ‘Cover Sheets’. This folder should contain one cover sheet per sampled candidate.

Each cover sheet should be clearly identified as relating to a specific candidate’s work.

CS_[centre #]_[candidate #]_[first two letters of surname]_[first letter of first name]

Should I test the CD prior to despatching it to the moderator?

Yes. Prior to the CD being despatched to the moderator it should be thoroughly tested to ensure that the files have burnt to the CD correctly, and that all files within each folder can be accessed.

How should I label the CD that is sent to the moderator?

A label should be stuck on the top of the CD itself with the following information clearly marked:

UNIT, EXAM SERIES

CENTRE NUMBER, CENTRE NAME.

CENTRE CONTACT NAME,

TELEPHONE NUMBER AND EMAIL.

How do I send the CD with samples to the moderator?

The CD containing the candidates’ samples should be posted in an appropriately sturdy envelope to the nominated moderator. You should also indicate the unit and centre number on the envelope, above the moderator’s address details.

Should I send the CD Recorded Delivery or ordinary post?

CDs should be sent ordinary post and not recorded delivery, so that they may be received at the moderator’s address when he or she is not there. You should, however, obtain a proof of postage certificate from the Post Office. Please ensure that the envelope is small enough to fit through an ordinary letterbox.

How do I find out where to send the sample?

When submitting marks via Edexcel Online, click on the ‘Assessment Associates’ link to display the name and address details of your moderator.

Please ensure that where there are different moderators for different units the correct moderator and address details are used for the appropriate units.


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Do I need to send the CD with samples to Edexcel as well as my moderator?

No. You need only to send a copy of the CD to your moderator. If an additional copy is required you will be contacted directly by Edexcel and advised accordingly. For this reason, a back-up copy should be held securely at the centre. If CDs are to be sent directly to Edexcel for any reason this will be communicated to individual centres where required.

Will I receive the CD with samples back from the moderator?

No. The CD is treated as a copy, and so you must ensure that you have a back up stored securely within your centre.

How do I know that the moderator has received my samples or that moderation has been completed?

If samples are missing you will be contacted directly. You may be required to produce a proof of postage in order for the second copy to be accepted for moderation.

Important: CDs/sample folders which are not named, formatted, labelled or structured according to guidelines provided in this document will be returned to centres unmoderated. Under such circumstances, Edexcel cannot guarantee the timely issue of results for candidates entered.

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