Biology A2 Snab Coursework

February 2006

GCE Edexcel Advanced Subsidiary GCE in Biology (Salters-Nuffield) (8048)

First examination 2006

Edexcel Advanced GCE in Biology (Salters-Nuffield) (9048)

First examination 2007

Coursework guide

February 2006

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Edexcel Limited is one of the leading examining and awarding bodies in the UK and throughout the world. It incorporates all the qualifications previously awarded under the Edexcel and BTEC brands. We provide a wide range of qualifications including general (academic), vocational, occupational and specific programmes for employers.

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Acknowledgements

This specification has been produced by Edexcel on the basis of consultation with teachers, examiners, consultants and other interested parties. Edexcel acknowledges its indebtedness to all those who contributed their time and expertise to the development of Advanced Subsidiary/Advanced GCE specifications.

Authorised by Jim Dobson Prepared by Kath Skillern

Publications code UA016953

All the material in this publication is copyright Edexcel Limited 2006

Contents

Introduction 1

Visit or issue report (Unit 6133/01) 3 Introduction 3

Exemplars 3

Identifying and describing two aspects of biology 4

Account of biological principles 9

Communication 16

Student checklist (Unit 6133/01) 21

Practical work review paper (Unit 6133/02) 23 1 Safety and use of apparatus 24

2 Producing reliable and valid results 24

3 Significance of results/data 24

4 Presenting data 24

5 Using results to draw conclusions 25

Final advice 34

Choosing the best practical 34

Coursework investigation (Unit 6135/02) 37 Assessment criteria Research and rationale 37

Exemplar 1 Jennys work 38

Exemplar 2 Michaels work 40

Assessment criteria Planning 42

Exemplar 3 Samirs work 43

Exemplar 4 Robyns work 47

Assessment criteria Implementing 51

Exemplar 5 Marcos work 52

Exemplar 6 Shazias work 55

Assessment criteria Observing and recording 60

Exemplar 7 Susans work 61

Exemplar 8 Gabriels work 65

Assessment criteria Interpreting and evaluating 68

Exemplar 9 Jatinders work 69

Exemplar 10 Davids work 75

Assessment criteria Communicating 78

Exemplar 11 Rosannas work 79

Exemplar 12 Jans work 95

Exemplar 13 (maximum mark) Katharinas work 104

Student checklist for project skills (Unit 6135/02) 38

UA016953 Coursework guide Edexcel Advanced Subsidiary/Advanced GCE in Biology (Salters-Nuffield) Issue 1 February 2006

1

Introduction

Edexcel is pleased to offer this coursework guide to support teachers in their work with students for the assessment of the AS units 6133/01, 6133/02 and the A2 unit 6135/02.

Examples of students work have been obtained from the pilot cohort September 2002 to June 2004. The assessment is based on the criteria published in the Advanced Subsidiary and Advanced GCE in Biology (Salters-Nuffield) 8048/9048 specification.

The examples used in this guide have been assessed by Edexcels senior examiners. Edexcel wishes to thank the schools, teachers and students who participated in the production of the exemplar material.

All of the examples used in this coursework guide have been made anonymous and any names given are fictional.

In addition to this coursework guide there will be further support from a consultancy service and a series of professional development meetings. For more information please contact Edexcel on 0870 240 9800 or visit our website at www.edexcel.org.uk or the Heinemann page at www.advancedbiology.org.


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3

Visit or issue report (Unit 6133/01)

Introduction

Those schools involved in the pilot of these qualifications (20022005) should note that these new specifications are slightly different for Section B.

One strand, (a), still deals with the biology involved for the visit or issue and should be straightforward.

However, another strand, (b), now looks at future developments and also refers to uses which can be taken as methods employed by biologists. Students can either look entirely at future developments, entirely at uses (meaning methodology) or at a combination of the two as long as the future developments are clearly linked to the uses described.

The third strand, (c), now requires students to evaluate critically the validity of the information gained whether from websites, books or the person(s) conducting the visit.

Note: quotes from students work in bold italic are only a small percentage of the actual work submitted and are for illustrative purposes only.

Exemplars

We have provided five examples (A-E) of student work that the moderator has commented upon. Quotes from the students' work are highlighted in bold. The moderator has identified where and why marks have been awarded in relation to the assessment guidance, and has offered a final commentary with suggestions for improvement.

Exemplar A A visit to Batemans Brewery.

Exemplar B A visit to Cranfield University for prospective A-level students to give an insight into biology as a career.

Exemplar C Deforestation: the global assault continues.

Exemplar D Information leaflet on glaucoma.

Exemplar E Biology issue report.


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Identifying and describing two aspects of biology

A Identifying and describing two aspects of biology Total marks

a The purpose or significance of two aspects of biology are described within the context of the chosen visit or issue.

b There is some appreciation of the ethical, social, economic or environmental implications of the biology encountered within the context of the visit or issue.

2 marks

a The significance of both aspects of biology are described clearly within the context of the chosen visit or issue.

b There is a clear explanation of the ethical, social, economic or environmental implications of the biology encountered within the context of the visit or issue.

4 marks

Exemplar A A visit to Batemans Brewery

Student A produced one of the best visit or issue reports in the first two years of the GCE in Biology (Salters-Nuffield) pilot, gaining the maximum mark of 20. The two aspects of biology they connect were The Raw Materials for Brewing and Fermentation. On the first page of student As report they not only identified both of these but also indicated on which pages they were to be found.

Target Audience AS/A-level biology students

First Biological Principle The Raw Materials for Brewing (pages 2-4)

Second (major) Biological Principle Fermentation (pages 5-8)

Word Count 1435 words (not including Bibliography or Figures 1-4). Note Figure 1 contains 65 words.

Student A then went on to give quite a detailed account of malt (and how it is produced), water, hops and finings for their discussion of The Raw Materials for Brewing.

The embryo must be small (ie low nitrogen content) so that most of the ear is starch and large amounts of sugar can be extracted for fermentation.

Water composes 90% of the beer and therefore substantially affects flavour.

Hops are added in the copper, where the rolling boil physically breaks down the hops releasing the oil (containing the bitter flavour compounds lupulin and humulone) into solution.

Isinglass finings (collagen from the swim bladder of fish) are added during conditioning.


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The main aspect for student A was Fermentation. They gave a very detailed account of:

the importance of glycolysis, with diagrams and details of the biochemistry involved

the three strains of yeast used and how infections by wild yeast or bacteria were prevented

the importance of temperature for fermentation, ie warmer temperatures mean more unpleasant by-products such as esters and diketones

specific gravity changes secondary fermentation and other uses of fermentation.

Fermentation takes place in large vessels at a controlled temperature (lower temperatures produce fewer by-products, warmer more eg esters and diketones, which have low flavour thresholds ie humans can taste them at very low concentrations therefore if concentrations change, sales may be affected) and pH (optimum conditions).

The yeast is checked every week for infection under the microscope.

These details meant student A gained two marks for strand (a).

Student A also gained two marks for strand (b). Ergot contamination was discovered, meaning the malt had to be checked to ensure it was safe for human consumption. The environmental advantages of using organic grain for malt, ie no chemical fertiliser or pesticides, were also considered.

Environmentally speaking, this was good (no added fertilisers or pesticides) but organic grain is inconsistent with varying size, nitrogen and starch content.

The economics of using organic grain, which is more expensive, and the use of isomerised hops were also considered. They both improve the consistency and quality of bitterness but are more expensive for the small brewery.

For Fermentation, student A showed how excess yeast is sold to farms or the local Marmite factory, ie disposed of in an environmentally friendly way, with economic benefits for the brewery:

Yeast is reused at the brewery. Excess yeast is sold to farms or the nearby Marmite factory ie yeast is disposed in an environmentally way and fewer of the earths resource are used.

Student A also talked of mechanical carbonation of the beer being too expensive for the small brewery.

Total: 4/4


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Moderators comments

Maximum marks were gained for strand (a) because both aspects were discussed and analysed in some detail. The importance of both for the successful brewing of beer was also made clear throughout the report.

Maximum marks were gained for (b) because at least two economic, environmental, social or ethical considerations were looked at for both aspects.

Exemplar B A visit to Cranfield University for prospective A-level students to give an insight into biology as a career

Student B identifies the Significance of Two Aspects of Biology: Animal Testing and Tumour Marking on page 2 of their work, but then on page 4, they identify two more biological principles as Polymerase Chain Reaction and Gel Electrophoresis there was no hint in the title and it was difficult to work out what the report was concentrating on.

For strand (b), there was some discussion of ethics in that the Christian view of animal experimentation was briefly discussed and there was some mention of the cost of research projects:

Testing on animals for cosmetic purposes takes place for products like shampoo using the draize test. Many people believe that animals should not be used in this way for commercial purposes.

However, neither of these was actually tied to the two principles highlighted, namely Polymerase Chain Reaction or Gel Electrophoresis. Consequently, strand (b) gained zero marks.

Total: 1/4

Moderators comments

Student B gained only one mark for strand (a) because four principles were described yet only Gel Electrophoresis was dealt with in any great detail, showing how it was relevant to the work of Cranfield.

Strand (b) should have had at least two of social, economic, environmental or ethical issues discussed for each of the two biological principles. In this case, it was impossible to work out which two aspects the student was concentrating on since four were unidentified.

In order to gain higher marks the student would need to:

make the two principles more obvious, preferably on page 1 in the title make sure that both principles are discussed in reasonable detail, and also make

sure that it is obvious how important both are to the work undertaken at Cranfield

discuss at least two of social, economic, environmental or ethical issues for each of the two biological principles. The ethics of Gel Electrophoresis or Polymerase Chain Reaction themselves are hardly an issue, but the costs might be, as would the social implications of treating cancer successfully.


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Exemplar C Deforestation: the global assault continues

Although student C uses subtitles such as Environmental Impacts or The Economic Struggle, they also used other subtitles which made it impossible to identify the two main biological principles under investigation. Consequently strand (a) scored zero marks.

However, strand (b) scored two marks because, although the two aspects were not identified clearly, there was a lot of discussion on the environmental impact, economic effect and also many social aspects such as urban migration and employment generation.

Another extremely concerning deforestation impact is genetic erosion. This is the loss of genetic diversity within a species caused by human activities and environmental changes.

Faced with political decisions about urban migration, food production, employment generation, national security, economic structural adjustment and all the other issues that demand their attention, many governments have opted to ignore deforestation.

Total: 2/4

Moderators comments

Student C did not clearly identify the two aspects of biology under investigation.


identify clearly the two aspects of biology being considered and then discuss at least two of ethical, social, economic or environmental implications for each aspect.

Exemplar D Information leaflet on glaucoma

Student D produced an information leaflet on glaucoma and how cannabis could be used in its treatment. Two marks were awarded for strand (a) because glaucoma and cannabis were described as the two biological aspects to be covered in the leaflet.

This is an informative leaflet that explains the problems associated with glaucoma, and explains how the use of cannabis can help.

Also, both aspects were dealt with in reasonable detail and the significance of each was spelt out. Only one mark was awarded for strand (b) because, although both the ethics and social advantages of using cannabis were discussed, there was no mention of the social or economic issues associated with untreated eye diseases such as glaucoma.

Total: 3/4


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Moderators comments

Student D clearly identifies the two aspects of biology under investigation. In order to gain a higher mark the student would need to:

mention that untreated diseases, such as glaucoma, could result in premature blindness and remove a significant number of people from the workforce. This would then cost a lot in benefits and other taxpayers would have to support them. In addition, the social disadvantages of having more people dependent on others could have been looked at.

Exemplar E Biology issue report

Student Es report clearly identified the two aspects of biology under investigation and so scored two marks.

The purpose of this report is to investigate links between one form of cancer treatment and its associated influence on female infertility.

Only one mark was awarded for strand (b) because there was a discussion of the social implications and a reference to ethics but only for the idea of freezing ovarian tissue.

Opponents to this form of treatment may hold the view that it is interfering with nature

Total: 3/4

Moderators comments

Both aspects are identified and the relevance of both of these to female fertility is discussed.

There is nothing on the economics of the treatments. In order to gain higher marks the student would need to:

expand on the ethical discussion of the treatment and also include a look at the social implications for the individuals involved.


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Account of biological principles

B Account of biological principles Total marks

a There is a description of the biology relevant to their chosen aspect.

b There is a reference to future developments or uses in this area of biology.

c There is reference to information or arguments obtained from three or more sources.

3 marks

a There is a clear description of the biology relevant to their chosen aspect.

b There is some speculation as to future developments or uses in this area of biology.

c There is reference to the validity of the information or arguments obtained from three or more sources.

6 marks

a There is a discussion showing some understanding of the biology relevant to their chosen aspect.

b There is informed speculation as to future developments or uses of biology in this area of biology.

c There is some evaluation of the validity of the information or arguments obtained from three or more sources.

9 marks

a There is a clear discussion showing a thorough understanding of the biology relevant to their chosen aspect.

b There is discussion of possible implications of future developments or uses in this area of biology.

c There is a clear evaluation of the relative validity of the information or arguments obtained from three or more sources.

12 marks


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Student A gained four marks for strands (a) and (b) because they not only identified their main aspect as Fermentation on the first page, but went on to discuss a great deal more biological detail such as:

well set-out equations and discussion of glycolysis showing how ethanol is produced from glucose

a good discussion of the three strains of top-fermenting yeast used. Batemans uses 3 strains (mixed) of Saccharomyces cerevisiae (top-fermenting) yeast, the advantage of this being that the yeast collects on the top of the vessel, protecting the alcohol from oxygen in the air therefore preventing oxidation of the alcohol to acetic acid or vinegar.

The strain of yeast used must remain consistent resulting in consistent flavours.

the importance of temperature control for flavours the importance of the original specific gravity for final alcohol concentration the use of secondary fermentation to carbonate the beer other uses of fermentation to produce cheese, yoghurts, antibiotics or metal

extraction from low-grade ores.

Student A also gained four marks for strand (b), future developments or uses. For future developments, they pointed out that:

The yeast genome was sequenced in 1996, therefore genetic engineering may be used to create new strains of yeast with improved characteristics to increase the efficiency of fermentation and the flavour of the beer.

Student A speculated that this might also mean a decline in continuous fermentation and the use of higher gravity worts.

The term uses clearly refers to methods, ie what biologists actually do. Student A linked their discussion of biological principles to what actually happens at the brewery. Student A showed how the brewery used three strains of yeast and highlighted the advantage of top-fermentation. In addition, student A discussed the importance of controlling the temperature and how this is done, how the specific gravity falls and how the brewery uses a secondary fermentation in order to carbonate the beer.

Batemans only produces cask-conditioned beer ie beers that undergo a secondary fermentation whilst in a sealed container.

For strand (c), student A referred to her bibliography at regular intervals. For example, student A discussed how carbonation from a secondary fermentation is an advantage for a small brewery because buying in carbon dioxide is too expensive www.brewing.com/beer-carbonation/carbonation-methods.htm. Student A gained four marks for strands (a) and (b).


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In addition, as well as showing how the deliberate lowering of the temperature to 9oC once the specific gravity has reached 1.010o helps to keep some glucose available for the secondary fermentation, student A compared the fall in specific gravity with that of another brewery.

Also data from another brewery (Highwood) is similar, with specific gravity falling from 1.045o to 1.009o overall.

Student A also used reference material to question the future use of continuous fermentation as a result of genetic engineering of yeast, www.mbaa.com/TechQuarterly/Abstracts/1977/tq77ab33.htm.

Total: 12/12

Moderators comments

Maximum marks were obtained because student A not only provided a great deal of biological information about glycolysis and fermentation but also speculated about the implications of genetic engineering for the future of brewing.

Student A also looked at the methods actually employed at the brewery and critically used her reference material either to make a point or to compare the claims of one brewery with those of another.


In his report on the visit to Cranfield University, student B did not state the main biological principle they were investigating, but it was taken to be Gel Electrophoresis. Student B gained two marks for strand (a) because, although there was quite a lot of biological detail in the report as a whole, only a small amount was actually relevant to Gel Electrophoresis, ie structure of DNA or size of DNA fragments after cutting with restriction enzymes.

Gel Electrophoresis is used for the identification of particular DNA molecules by the band patterns they yield after being cut with various restriction enzymes.

For strand (b), there was no mention of future developments for Gel Electrophoresis or PCR but there was a brief discussion of how Gel Electrophoresis was carried out, which gained one mark.

An agarose tank is prepared, acting as a support for separation of the fragments of DNA. Holes in the gel hold the DNA solution.

There was a brief look to the future for alternatives to toxicology, but this was not identified as the main biological principle and so could not be credited with a mark.

For strand (c) there were five references but none were mentioned in the text. Acknowledgement would have gained an extra mark for strand (b) but, in this case, there was no critical evaluation.

Total: 3/12


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Moderators comments

The discussion of Section B was too descriptive. The main biological principle was not identified and a considerable amount of the

biological detail involved was not relevant to Gel Electrophoresis, the principle chosen.

There was no look at the future, and methods or uses were described only briefly.

Three or more references/sources/materials were not analysed critically. In order to gain higher marks the student would need to:

identify the main biological principle of the visit or issue give far more biological detail relevant to the main biological principle. In fact, it

might have been better to have chosen Polymerase Chain Reaction as the main principle for discussion

discuss future developments or improvements relating to Gel Electrophoresis, or the methods involved, with more detailed analysis

look at far more critically at least three references or sources. For example, the Cranfield University information pack is mentioned, but there is no questioning of the claim that a safe effective drug results from the clinical trials? A cancer research website was listed and, although examples of tumour markers were given, there was no indication of how effective these were or indeed how they worked.


The main principle under investigation was not identified by student C, but in the deforestation report there was some discussion of:

drought and soil erosion climate change loss of biodiversity loss of plants as a potential for medicines genetic erosion poverty.

The antiseptic phrase loss of biodiversity masks the fact that the annual destruction of millions of hectares of tropical forests means the extinction of thousands of species and varieties of plants and animals

However, the discussion was brief and somewhat descriptive, with insufficient explanation of biological treatment, and scored only two marks for strand (a). Strand (b) scored zero marks because there was no discussion of what biologists were actually doing about deforestation and there were only a couple of lines about the future, with a brief mention of the World Wide Fund for Nature.

Environmental organisations like WWF and Friends of the Earth are tying to help save forests by campaigning for their urgent protection.


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Strand (c) also scored zero marks because, although there were several reference sources, none were used in the text and there was no attempt to use this reference material to check on the validity of the information used. The report, as a whole, was descriptive rather than analytical.

Total: 2/12

Moderators comments

The report was actually far too short, being only about 1000 words. In order to gain higher marks the student would need to:

use the full 2500 word limit. This would allow far more detailed discussion, especially of the biology involved. This could have been a more detailed look at climate change or the importance of the forest habitat to species such as the orang-utan, eg what tree species are most important

clearly identify the main biological principle under investigation speculate on the future developments associated with deforestation, eg

reforestation or a more detailed look at what WWF or Friends of the Earth are actually doing. In addition, look at methods used by biologists. If biodiversity is the main aspect, then it would be reasonable to include reference to seed banks or zoos as a way of preserving some species

use the reference material, ie both refer to it and examine it critically. For example, a website reference to the World Resource Institute is given as www.wri.org but there is no discussion of what this organisation is doing. Another is www.rcfa-cfan.org/english/info.tree.html and includes details of how the Canada Fund for Africa supports forestry and agroforestry research in Africa. Yet this is not mentioned in the text or commented on.


This information leaflet on glaucoma gained only two marks for strand (a). Firstly, student D did not identify the main principle that this leaflet was describing. Since the details of glaucoma were rather descriptive, the use of cannabis was taken to be the main principle. There was a brief discussion of the chemistry of THC (tetra-hydro cannabinol) together with some of the medical problems that it could be used to treat, eg as an antinausea drug or as treatment for glaucoma.

Once THC has entered the blood stream, it travels around the body until it reaches the brain. Here it attaches itself to cannabinoid receptors and its effect is felt.

Strand (b) only gained two marks because there was no mention of future developments at all, but there was some discussion of how cannabis is used medicinally.

If cannabis is smoked through a vaporiser, the THC is vaporised and nearly all the carcinogens are left behind.


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Strand (c) scored zero marks because there were only five reference sources, which were impossible to follow up because of lack of detail, and in the text they were not acknowledged or discussed critically.

Total: 4/12

Moderators comments

The discussion of Section B was too descriptive. In order to gain higher marks the student would need to:

identify the main aspect clearly, in this case, how cannabis is used to treat diseases such as glaucoma

provide a much more detailed biological background for cannabis itself, how it affects the body and, also, how it alleviates some of the disease symptoms. For example, student D does discuss how cannabis dilates blood vessels and explains how this might help with glaucoma. However they could have expanded on this to explain how this might help with the other diseases mentioned, ie asthma, obesity

either give more examples of how cannabis could be used or speculate more about its possible future use. For example, if it dilates blood vessels, could it help with hypertension?

critically analyse some of the reference material and certainly make it possible for the reader to follow it up. For example, the word proven is used for cannabis easing the effects of glaucoma did only one reference suggest this or several, and what sort of agreement was there?


The main principle was not identified by student E but strand (a) gained three marks because there was a reasonable discussion of the biology associated with ovarian tissue banking and the problem of cancer cells remaining in the tissue sample taken.

Ovarian tissue contains follicles and immature eggs and the preserved tissue can be transplanted back to the donor to allow the women to produce human eggs.

Strand (b) gained four marks because there was quite a lot of detail on methodology and, also, there was a comment on future developments.

Unfortunately further studies are required to determine the best option for fertility treatment as there are safety concerns.

Whilst this experiment has not yet been successful on humans, a monkey in Oregon has recently become pregnant following the treatment, and researchers are confident that their findings show that there is potential for normal ovarian function to be restored to cancer patients.


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Strand (c) only just received one mark for the following comment. However, the comment was not followed up.

The fertilised embryo developed to the four cell stage and was implanted into her womb but she did not become pregnant. Despite this, researchers say the findings prove the value of long-term tissue banking.

Total: 8/12

Moderators comments

There was a good discussion of the biology involved. There was quite a detailed look at the methods used and possibilities for the

future.

There was a very brief look at the reference material used. In order to gain higher marks the student would need to:

clearly identify the main principle being considered so that relevant discussion of the biology involved can then be credited

be much more critical of the reference material being used, eg when discussing the work of Kuluk Otkay on ovarian tissue banking

use research methods to try to find out who else is working on this and compare their success claims or methods used.


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Communication

C Communication Total marks

a The organisation and layout of the report shows evidence of some planning for the intended audience, with use of some appropriate graphs, tables, diagrams or photographs and technical terms, used mostly correctly, where appropriate.

b Spelling, punctuation and grammar are largely correct, all sources used are acknowledged and not used excessively and the presentation is mostly clear and logical. This is the maximum mark available for reports which exceed 2000 words.

2 marks

a The organisation and layout of the report is well planned for the target audience and is enhanced by carefully selected graphs, tables, diagrams or photographs and correct use of appropriate terminology where appropriate. Sub-headings of graphs, diagrams and tables are appropriate and helpful.

b Spelling, punctuation and grammar are correct, all sources used are fully acknowledged and used selectively and the presentation is logical and concise. The report is within the word limit of 2000 words.

4 marks


On the first page, where student A identified two aspects, they also noted the audience to be AS/A-level students. Although not particularly original, they did write reasonably simply and include lots of tables, pictures, graphs and diagrams. Their impact was also broken up with subheadings in more of a magazine format and none of the pages was just solid text. Student A gained two marks for strand (a).

In addition, for strand (b), the spelling, punctuation and grammar were excellent and the report was concise, well-written and easy to read (1435 words). Not only did student A include seven references to books or websites, they also acknowledged these in the text. For example, when discussing clarification of beer, a reference was given in the text using a footnote 2 for the second reference, in this case to www.beer-brewing.com.

Total: 4/4

Moderators comments

The audience was identified and the write-up appropriately targeted. Not only were several websites or book references given, but they were also

referred to individually in the text, ie it was easy to see where the information had come from and it was easy to follow it up.


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The visit by student B to Cranfield University was directed at prospective A-level students and the report was reasonably well set-out with diagrams and subtitles. This scored two marks for strand (a).

The report aimed at giving prospective A-level students an insight into careers associated with biology.

However, although there were five references to websites, which gained one mark, none were acknowledged or discussed in the text.

Total: 3/4

Moderators comments

See above. In order to gain higher marks the student would need to:

ensure that references used were acknowledged and referred to in the text.


The audience was identified clearly as GCSE students by student C, but the report was not particularly well set-out. Only two pictures were used, with a few subheadings and no graphs or diagrams to illustrate the point being made. It would not have been a very interesting read for the intended audience, and so scored only one mark for strand (a). Strand (b) also scored one mark because although there were nine references to books or websites, none were acknowledged or referred to in the text.

Total: 2/4

Moderators comments


make sure that the report is suitable for the intended audience. In this case, more pictures or diagrams could have been used and more subheadings would have broken up the text

acknowledge the references in the text. For example, a website address could have been included for the photograph of the orang-utan representing the loss of biodiversity.


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The audience was identified by student D as older people who might be in an opticians or doctors waiting room, but the leaflet was not that well-written or clear. It is unlikely that older people would have found it easy to follow and strand (a) scored only one mark. Strand (b) also scored one mark, because references were difficult to follow up and were not acknowledged in the text.

Refer madness book.

Two pictures were used, but it was not obvious where they had come from.

Total: 2/4

Moderators comments


ensure that, if the audience is to be older people, the leaflet must be easier to read and more attractively laid out with subheadings etc. Potential glaucoma sufferers might also find the print size and font difficult to read

ensure references are clear and acknowledged in the text. For example, the two diagrams could have had a website or book reference. Also, fewer than 1500 words were used and extra words could have been useful in giving greater detail of the biology involved in cannabis action.


The audience was not identified clearly by student E.

It is a report intended for newspaper publication.

Not only was the target audience unclear, but the presentation of the report was very dull. There were no subheadings or diagrams and only one photograph of the doctor himself, which was not particularly informative. Consequently, strand (a) scored zero marks. Strand (b) scored two marks, but only just. This was because there were five website references, which were referred to.

With Otkays work, we appear to be much closer to the day when a young woman diagnosed with cancer can both survive and subsequently have children said Marian Damewood MD.

Total: 2/4

Moderators comments

See above.


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be much more specific about the intended audience, ie tabloid newspaper or broadsheet, general front page story or specialist article?

make sure that the style, presentation and readability of the article are suitable for the audience

ensure that references are used and acknowledged in the text. In this case, by simply putting the website address next to the relevant paragraph or using a footnote.


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Student checklist (Unit 6133/01)

Make sure that two aspects of biology are clearly identified and that the relevance of both of these to the issue or visit is described.

Ensure that at least two of ethical, social, environmental or economic issues are described fully for both of the biological aspects.

Clearly identify the main biological principle under investigation for Section B. Thoroughly examine the biology involved for this main aspect. Consider, in detail, the future developments for this aspect and/or the methods

used.

Comment critically on the information obtained from references given in the bibliography.

Clearly identify the intended audience for the report and make sure that the report is suitable for that audience.

Break up the text using relevant pictures, diagrams or subheadings so that the report is a good read.

Ensure that several references are given and that they are acknowledged in the text.


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Practical work review paper (Unit 6133/02)

As an alternative to the GCSE style of practical coursework, the A/AS GCE in Biology (Salters-Nuffield) specification offers the practical work review paper. The idea is to allow students to enjoy and learn from their practical work, without having the worry of constant assessment. Assessment is later on and is in a form which can build on work done in the course.

Ten pieces of practical work are designated in the specification as core practicals.

1.1.17 Describe how the effect of caffeine on heart rate in Daphnia can be investigated practically.

1.2.3 Describe how the effect of temperature on membrane structure can be investigated practically.

1.2.11 Describe how enzyme concentrations and substrate concentrations can affect the rates of reactions and how the effect of enzyme concentration on reaction rate can be investigated practically.

1.2.17 Describe how Gel Electrophoresis can be used to separate DNA fragments of different length.

2.3.6 Describe the stages of mitosis and how they can be observed practically.

2.3.13 Describe how the expression of a gene can be demonstrated practically by induction of galactosidase.

2.4.7 Describe how to determine the strength of fibres.

2.4.9 Describe how to investigate the antibacterial properties of plants.

2.4.17 Discuss the possible relationship between CO2 levels and global warming and how this can be investigated practically.

2.4.22 Describe how to investigate the effects of temperature on the development of organisms (eg plant growth or brine shrimp hatch rates).

Strictly speaking, the definition of a core practical is one that can be used as the basis for a question on the theory paper (Unit 1 or Unit 2). In practice, these 10 pieces of work, which have to be carried out, are likely to form the basis for work on paper 6133/02. Also, students have to choose a piece of practical work to support their answers to each of Questions 2 and 3 on this paper. This can be the same piece of work but, again in practice, it is unlikely that this would be the best approach. For Question 1, any practical work done in the course can be referred to.

Paper 6133/02 will assess students abilities to see elements within their practical work that are common to most good science in this subject at this level. In that sense, it builds on the work that most students will have done at GCSE level on the nature of scientific enquiry. The specific requirements are on pages 2829 of the specification (January 2005) and are reproduced here.


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1 Safety and use of apparatus

Students should:

be able to comment critically on the suitability of apparatus for carrying out specific practical tasks in order to achieve measurements appropriate to the investigation

have an awareness of safety in the use of apparatus during their practical work, consider the ethical issues arising from the use of

living organisms and for the environment.

This could be in the context of an evaluation of practical work they have taken part in or when planning a new investigation.

2 Producing reliable and valid results

Students should:

appreciate that appropriate observations have to be made to validly test a hypothesis or idea

appreciate that variables need to be identified, including both dependent and independent variables, and, where possible, controlled or otherwise allowed for

be aware that valid results are derived through precise, repeatable measurements or observations, made with apparatus and experimental procedures that are suitable for the task

be aware that errors in readings can be systematic (values differing from the true value by the same amount) or random (values lying equally above or below the true value).

3 Significance of results/data

Students should realise that the significance of differences or trends within data is dependent on the degree of error within the experiment.

4 Presenting data

Students should be able to discuss the most appropriate methods for presenting data in order to identify trends and patterns clearly, and to an appropriate degree of accuracy.


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5 Using results to draw conclusions

Students should appreciate that statements, explaining trends and patterns in data from an investigation, should be supported by evidence from the data and from their own biological knowledge. The validity of a conclusion is dependent on the experimental method used and the quality of the results obtained.

The review will require students to refer to the accounts they have made of the practical activities carried out in Units 1 and 2. Students may have to include examples of data tables, graphs or other relevant information in carrying out their practical work review. They will have to submit to Edexcel the completed practical work review and the complete accounts of two practical activities that have been used as evidence.


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Examples of questions, taken from June 2004 Unit 6133 Paper 02; these have been used in the specimen papers.

Question 1

General principles of good science are tested in this question. Examples may be asked for and can be taken from anywhere in the AS specification.

Topics covered to date (June 2005) include:

accuracy in measuring dependent variables pre-treatment of experimental organisms ethical issue of using organisms reliability types or error (as identified in the specification). In answering this question students have, in the past, referred to a wide range of practical work. Below is a list of the most popular ones:

heart rate of Daphnia beetroot membrane enzyme concentration CO2 and temperature rise. June 2004, Question 1:

(a) Describe what is meant by random error and give an example where your experimental results were affected by random error.

(b) Distinguish between the accuracy and the reliability of results.

(c) Explain how you would ensure that any results you obtain are reliable.

Example 1 Part 1 (a):

Unfortunately the above answer does not gain any marks because it does not show understanding of the meaning of the required term and, therefore, neither addresses it nor gives a suitable example.


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However, the answer below shows a clear understanding of the relevant term and gives a good example.

Example 2 Part 1 (b):

The above answer does not attempt to define the terms asked for and, therefore, it does not score any marks.

However, the answer below provides clear definitions for both terms and, therefore, scores two marks.


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Example 3 Part 1 (c):

The above answer struggles to score one mark, which has been awarded for the idea that the experiment needs to be repeated many times. The student shows little evidence of having understood what reliability means in this context.

However, in the answer below a clear understanding is shown.

Question 2

This requires a specific practical activity to be referred to and then used to answer the questions. In this way, it does not differ from Question 3 and, therefore, both questions are two of a kind.

Practicals used in the past to support this question (and Question 3) include:

heart rate of Daphnia beetroot membrane enzyme concentration CO2 and temperature rise antibacterial properties of plant extracts strength of plant fibres. June 2004, Question 2:

From the practicals that you have completed during the course, select one suitable practical report to support your answers to the following questions:

(a) explain what is meant by the following terms:

(i) Dependent variable.

(ii) Independent variable. (2 marks)

(b) identify the dependent variable in your report, and state how you ensured it was measured to a suitable level of accuracy. (3 marks)

(c) describe how one other variable was or could have been controlled, and how it may have affected your results. (2 marks)


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The above is a full mark answer, but the student has spent a lot of time getting there, largely because they have misjudged the amount of detail needed (only two marks are available) and have not noticed that examples do not have to be quoted.

However, the answer below does not include anything useful and just quotes the two terms at each other.



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The answer on page 29 is a good answer, with reference to a suitable piece of apparatus, a suitable variable and detail about its proper use. Students need to constantly be looking at mark allocations for questions and parts of questions in order to provide the necessary amount of detail. There are three marks available here and it is clear what is wanted. One is obviously for correctly identifying the dependent variable, which then leaves two marks to be gained. Just identifying the apparatus used is not enough to gain both marks. In addition to identifying the apparatus, students should be aware that accuracy is ensured by choosing suitable equipment and using it properly, which will give students the two marks. Many failed to get three marks for missing this last point.

The answer below fails to get any marks because of the fundamental mistake of choosing the wrong variable as dependent. In one way this may seem harsh, but it has to be remembered students have the paper for a week before they need to answer the question.

Example 6 Part 2 (c):

The above answer achieves one mark for the fairly poor attempt to suggest the effect that changes in temperature may have in an investigation where the independent variable is caffeine. No attempt has been made to suggest how the variable might be controlled. This could be a failure to read the question properly and take account of what it required. It is a common error in this type of question about confounding variables.


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The above answer is clearly weak at most levels. However, laboratory air movements might cause some problems. So the real difficulty here is not the rather poor choice of variable but the lack of any attempt to specifically identify what it might do to the data or how it might be controlled. Creating anomalies in my results or (in other answers) affecting my results or similar vague comments will not achieve any marks on their own. Something specific in relation to the chosen practical is always going to be needed. This answer seems to be hinting that temperature might not have been controlled as desired and so a temperature-related effect on, for example, heart rate or rate of enzyme reaction could have been discussed.

Question 3

This question is similar in type to Question 2.

June 2004, Question 3:

From the practicals that you have completed during the course, select another suitable practical report to support your answers to the following questions:

(a) Explain two procedures or precautions that you took to ensure safe working. You are reminded that these should specifically refer to the practical you have chosen. (2 marks)

(b) Explain why the graph you have drawn is the most appropriate way of displaying your results. (5 marks)


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Relatively simple questions about safety can sometimes yield less than full marks. Clearly, the practical chosen to support the answer can have a bearing on this. It might be that the safety issues involved are few and not a great deal of explanation is needed.

In this case, it might have been better to choose a different piece of work. It is appreciated that any such choice will be a compromise. An answer such as the one below suggests that the student was making up the safety points as they went along. One just convinces the examiner, but the other one is judged to be too trivial. More forethought might have led to a better discussion of ideas.

Any practical work involving the manipulation of bacteria is likely to yield a good score in terms of safety questions, as in the answer below.


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Scattergraph was crossed by the examiner in responses to this question. This is a mistake in MS Excel, where line graphs are referred to as scattergraphs. Students should be alerted to this.

Below is a full mark answer (as were many on this question).

Below is another full mark answer.

This student has made a reasonable, but vague, point about visual representation in the first paragraph; however, the marking point (9) is gained later. The mark is given for a line graph and this is often where the examiner has to check the appended experimental report to make sure that this is true. After that, the student simply repeats themselves and gains no further credit.


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Final advice

It is important to review the relevant sections throughout the course. Students who know exactly what they are to be examined on will do much better; they will avoid making false statements and making things up.

Care should be taken when selecting practicals in light of the questions set in any particular year. Guidance is given in the table on page 35 as to the appropriate core practicals to choose.

Students must make good use of the week prior to sitting the paper to make appropriate choices. Teachers can give generic advice, but must not, of course, tell students what to do at any stage.

Choosing the best practical

Summary of the main assessable topics

A Choice of apparatus/method etc, to ensure appropriate/precise measurements.

B Safety.

C Ethics of experiments and observations.

D Reliability (aspect of validity).

E Identification, control and/or measurement of independent variable and dependent variable.

F Identification, control and/or measurement of other variables.

G Error types.

H Dependency of significance of trends etc on degree of error.

I Data presentation methods (graphs, tables, bar charts, etc).

J Drawing conclusions from data.


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Main assessable topics

Core practicals Units 1 and 2 A B C D E F G H I J

1.1.17 Describe how the effect of caffeine on heart rate in Daphnia can be investigated practically

3 3? 3 3 3 3 3 3 3 3

1.2.3 Describe how the effect of temperature on membrane structure can be investigated practically

3 3? 3 3 3 3 3 3 3 1.2.11 Describe how enzyme concentrations and substrate concentrations can affect the rates of reactions and how the effect of enzyme concentration on reaction rate can be investigated practically

3 3 3 3 3 3 3 3 3

1.2.17 Describe how Gel Electrophoresis can be used to separate DNA fragments of different length

3? 2.3.6 Describe the stages of mitosis and how they can be observed practically 3? 3 3? ? 2.3.13 Describe how the expression of a gene can be demonstrated practically by induction of galactosidase

? 3 3 2.4.7 Describe how to determine the strength of fibres 3 3 3 3 3 3 3 3 3 2.4.9 Describe how to investigate the antibacterial properties of plants 3? 3 3 3 3 3 3 3 3 2.4.17 Discuss the possible relationship between CO2 levels and global warming and how this can be investigated practically

3 3? 3 3 3 3 3 3 3 2.4.22 Describe how to investigate the effects of temperature on the development of organisms (eg plant growth or brine shrimp hatch rates)

3 3? 3 3 3 3 3 3 3 3

Key: 3 = Yes

3? = Maybe

? = Probably not = No


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Coursework investigation (Unit 6135/02)

Assessment criteria Research and rationale

A Research and rationale Total marks

a There is some attempt to provide a rationale for the choice of investigation in terms of its scope and its relation to biological principles.

b Few sources are consulted and their scope is limited in providing a context for the investigation, to assist with the planning or execution of laboratory or field work, or in informing the interpretation of results.

2 marks

a There is a partial rationale for the choice of investigation. The biological background to the investigation is developed to some extent.

b Information gathered from some relevant sources has some bearing on the context for the investigation, and assists, in a limited way, with the planning or execution of laboratory or field work, or to inform the interpretation of results.

4 marks

a The rationale for the investigation is clear, in terms of its scope and relationship to biological principles.

b Several relevant sources are consulted, and are used to provide a context for the project, to assist with the planning or execution of laboratory or field work, and to inform the interpretation of results.

6 marks

a The rationale for the investigation is clearly justified in terms of its scope and appropriate biological principles are discussed.

b Additional sources, beyond those that were most readily to hand or were initially suggested by the teacher are selected. The material chosen is selected for its relevance to the investigation and it is used effectively to provide a context for the project, to assist with the planning or execution of laboratory or field work, and to inform the interpretation of results.

8 marks


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Exemplar 1 Jennys work

The effect of different concentrations of alcohol on streptomycin

Abstract: Within this experiment the relationship between different concentrations of alcohol and the effectiveness of antibiotics is studied. This is done using lawns of bacteria, agar impregnated with different alcohol concentrations and antibiotic discs. The results showed an increase in the efficiency of the antibiotic with increase in alcohol concentration although the result was not significant at the 95% level. Introduction: Does it matter if you drink alcohol whilst on antibiotics? Does it have any direct affect on the antibiotic? Does the amount you drink have any correlation with antibiotic efficiency? It is generally accepted that alcohol should not be consumed whilst taking any form of antibiotic, but is this fact or an old wives tale? This experiment uses the antibiotic streptomycin, the bacterium E.coli and absolute ethanol at different concentrations to investigate these questions. After preliminary research, it was recognised that high concentrations of alcohol would interfere with bacterial growth and would never be found in the body. I therefore researched the legal limit for alcohol concentration in the blood and decided to centre my experiment on these values. The values are 50mg per 100cm3 in some countries and 80mg per 100cm3 in others (17).

Streptomycin (above) is a human antibiotic drug derived from the soil bacterium Streptomyces griseus and is active against both Gram-positive and Gram-negative bacteria. It was originally isolated by Selman A. Waksman and Albert Schatz in 1947 and was found to be effective as a tuberculosis therapy (5). Streptomycin belongs to a group of drugs called aminoglycosides, which are effective against aerobic bacteria, viruses and fungi. This antibiotic works by inhibiting protein synthesis and damaging cell membranes in susceptible microorganisms, although it is not clear exactly how (5). It passes into the cell through Porin channels and attaches to the cells ribosomes causing it to produce ineffective proteins that are vital for the cells survival, so the cell dies (10). This antibiotic seemed appropriate to use in the experiment as it is effective against the bacterium E.Coli and is a human drug. It is likely, therefore, that both alcohol and this antibiotic could be present in the blood of the body. The bacterium used was Eshcherichia coli. In optimal conditions this bacterium can divide every 20 minutes, so can multiply from one cell to 108 in just 12 hours. It contains a 5 million base pair chromosome, so the copying of DNA has to be fast and accurate to result in only one mutation every billion nucleotides. Within the body E.Coli can be found living harmlessly in the large intestines of humans, living off any unabsorbed organic material (16).


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Preliminary Experiments.

Aims: To ensure the alcohol does not kill bacteria at these concentrations. To make sure the agar will solidify with the 5cm of solution. Bibliography: All websites accessed in March and April 2004 1. http://techniques.geog.ox.ac.uk/mod_2/tables//_pearsons_full.htm 2. http://health.iafrica.com/doconline/qa/pharmacology/800528.htm 3. http://www.acad.org.uk/04.html 4. http://pmep.cce.cornell.edu/profiles/exotoxnet/pyrethrins-ziram/streptomycin-

ext.html 5. http://www.factmonster.com/ce6/sci/A0846951.html 6. http://www.atdn.org/access/drugs/stre.html 7. http://www.cancer.org/docroot/CDG/content/CDGstreptomycin sulfate.html 8. http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&listiuds=1037

5408&dopt=Abstract 9. http://www.wikipedia.com 10. http://www.chclibrary.org/micromed/00037050.html 11. http://www.madsci.org/posts/archives/1068575560.Bc.r.html 12. http://ntri.tamuk.edu/cell/ribosomes.html 13. http://www.sciencestuff.com/nav/instructions/agar3.htm 14. Salters-Nuffield student book 2 15. Introduction to advanced biology Clegg 16. Biology sixth edition - Campbell and Reece 17. The Highway code - The stationery office 18. Chemistry data book- Longman 19. Micro-organisms and biotechnology - Taylor Total: 6/8

Moderators comments

Strand (a) the student has used biological principles to give a clear reason for doing the work. Sources were referenced to help develop the rationale.

Strand (b) some sources were referenced to help plan the work and interpret results that were not predicted.

Strand (b) was better than strand (a). In order to gain higher marks the student would need to:

use research methods to help make some suggestions as to how alcohol might inhibit the action of streptomycin

justify the use of E-coli as a model.


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Exemplar 2 Michaels work

Investigating the antibacterial effect that an ivy extract has on Bacillus subtilis

Abstract

This investigation was designed to demonstrate the antibacterial properties of ivy, this was done using a bioassay technique by pipetting 0.4mls of B.subtilis onto an agar plate and then carefully placing on the plate six pre-impregnated filter disks with different concentrations of 0% (control), 25%, 50%, 100%, 200% and 330% ivy extract. This was repeated on five other plates. The effect the ivy extract had on the bacteria could be seen after two days. The results showed that the lower concentrations 25+50%, encouraged bacteria growth where as the higher concentrations 100-330% did not stimulate bacteria growth but did not kill it either showing a bacteriostatic effect. The higher the concentration after 100% the smaller the bacteria growth around the filter disks. This method is easy to follow and implement. The ivy extract showed an effect on the bacteria, although it was not antibacterial at these concentrations, at the higher concentrations it showed a diminishing bacteriostatic effect and if concentrations were increased I think a bactericidal effect may well be found. If ivy extract was used as an antibacterial wipe the starting extract solution would have to be reduced to less than half the original volume.

Aim

The aim of this investigation is to demonstrate the antibacterial properties of ivy leaves.

Rationale

The majority of medicine originates from plants, the World Health Organization estimates that 75-80% of the worlds population uses plant medicines either in part or exclusively, an example of this is aspirin which was derived from willow bark [1].

I have chosen the ivy plant as it is available all year and there is a sustainable source of it nearby. I will be using the ivy leaves rather then the stems or roots as using the stems or digging up roots could kill the whole plant.

I think a bioassay technique would be very useful if you were trying to find a selection of plants that could be antibacterial if you needed to have some sort of wipe to contain an infection and you were in an unknown area without medical support. This experiment is therefore designed to give results over a short period of time that are decisive. In this investigation I will be using a bioassay technique where by the presence of the ivy extract is quantified by using living organisms. This will then show the strength of the antibacterial effect of ivy by showing areas of inhibition around the filter disks.

The active ingredient must be bactericidal to produce zones of inhibition on nutrient agar. This would show that the bacteria in a wound would be killed and stop an infection [11].

Ivy is a bitter aromatic herb; its leaves contain the compound emetine and triterpene saponins and are antibacterial [4].


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This bacterium is not considered pathogenic or toxic to animals, humans or plants therefore suitable for this experiment. They are rod-shaped bacterium and have a flagella and are gram positive in the early stages of growth [2]. This bacterium can be cultured on solid agar.

A culture B.subtilis will be grown on agar in a Petri dish on which discs of filter paper, impregnated with different concentrations of ivy extract, will be placed. The key to getting good results will be preparing and doing the experiment in as sterile environment as possible in a school environment.

Null hypothesis: the ivy solution will have no effect on the bacteria this would be indicated by having normal bacteria growing right up to the filter paper. There will be no significant difference between the two means.

Working hypothesis: the ivy extract will have a negative effect on the bacteria growth producing zones of inhibition as the ivy extract should contain a substance that is bactericidal.

Bibliography

[1] Salters-Nuffield Advanced Biology book 2, (Heinemann 2002), pg134

[2] www.epa.gov

[3] Advanced Biology, Michael Kent, 2000, pg370

[4] www.scs.leeds.ac.uk [5] Geography An Intergrated Approach, 2000, pg 636 for Spearmans rank significance graph.

[6] Cleapss laboratory handbook, 1989

[7] Salters-Nuffield Advanced Biology book 3 (Heinemann 2003), pg122

Total: 7/8

Moderators comments

Strand (a) the rationale is clear and related to appropriate biological principles. However, these could have been developed further.

Strand (b) additional sources were carefully selected and were used to help in planning the work and in discussing the results.


develop the biological principles of bacterial agents and/or bacterial growth.


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Assessment criteria Planning

B Planning Total marks

a There is some attempt to plan and to select the method or apparatus chosen. Some relevant variables are identified.

b Some potential safety hazards and the steps to avoid or minimise them are identified.

c A trial experiment may be carried out.

2 marks

a There is a plan for the investigation, with some explanation of the selection of apparatus and methods. There are some details of how variables are to be controlled, manipulated or taken into account and how relevant observations are to be made.

b Most potential safety hazards, and the steps to avoid or minimise them, are identified.

c A trial experiment is performed that has some bearing on the planning of the project.

4 marks

a There is a clear plan of action, both for an initial trial phase and for the main period of data collection. Apparatus selected and methods chosen are appropriate to the investigation. There is discussion about how variables are controlled, manipulated or taken into account and about the collection of relevant observations or data.

b All potential safety hazards are identified, and suitable steps taken to avoid or minimise them.

c A well-thought out trial is conducted in advance of the main data collection phase, and is used to inform the planning of the investigation.

6 marks

a, b, c There is evidence of thought and ingenuity in the design of experiments or the recording of data, with good attention to detail including the way in which variables are controlled, manipulated or taken into account and how relevant observations are made or data collected. Apparatus is devised or modified to suit the project as necessary.

8 marks


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Exemplar 3 Samirs work

A study to investigate differing pHs on the growth of pea plants

Aim: To investigate the affects of pH on the growth of pea plants. Introduction: In this investigation I intend to study the affect of pH on pea plant growth therefore ascertaining the best soil pH growing conditions. To carry out this experiment I must understand the mechanisms in a plant that are affected by differing pHs. I chose to study this investigation because of its significance in everyday life and pollution as an increasing concern. By studying the affect of pH on plant growth I am also therefore studying and acquiring a small amount of knowledge into the affects of acid rain. It is the industrial processes like the production of steel and iron and burning fossil fuels that are the main contributors to acid rain. This is because they produce the gases sulphur dioxide (SO2) and nitrogen dioxide (NO2) which are primary causes of acid rain. Acid rain can be defined as a general term encompassing dry deposition and precipitation which has an increased acidity due to contamination by carbon dioxide, sulphur dioxide and nitrogen dioxide. (K.Byrne Environmental Science) It is when nitrogen dioxide and sulphur dioxide react with the water and oxygen in our atmosphere form an acidic solution, which falls back down to earth as acid rain.

Sulphur SO2(g) + O2(g) SO3(g) Dioxide SO3(g) + H2O (l) H2SO4(l)

Nitrogen 3NO2(g) + H2O (l) 2H + 2NO3 +NO Dioxide NO + NO2 + H2O 2H + 2NO2

When deciding on a range of pHs to do in my experiment I took my inspiration from both previous investigations and nature. I found values as low as pH3 have been recorded in Southeastern USA (environmental protection agency). And pHs as high pH12 in the saline lakes of Kenya/Tanzania (B.E.Jones, W.D.Grant). I decided to do a range of pH 2 pH10 as a compromise. To carry out this experiment it is essential to understand the mechanisms within a plant that may be affected by any changes in pH. Background information: Photosynthesis: 6CO2+ 6H2O C6H12O6 + 6O2 Plants gain their source of energy and material to synthesise their growth materials in form of glucose, made by the light requiring process of photosynthesis. There are two parts to the photosynthetic process; both take place in the choloroplasts inside the cell. The two stages are the light dependent stage, which takes place in the thylakoid membranes of the grana, and the light independent stage.


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The Calvin cycle, in the light independent stage, relies on the help of enzymes where ATP and reduced NADP help turn carbon dioxide into glucose, amino acids, lipids e.t.c which provide the plants with its food. The Calvin cycle: (diagram omitted) The Calvin cycle cannot take place without the action of the enzyme ribulose biphosphate carboxylase (RuBISCO), the commonest enzyme in the world. The RuBISCO fixes carbon by combining Ribulose Biphosphate (RuBP) with CO2. Studies have shown that the optimum pH for the enzyme RuBISCO is 8.2. (www.clas.ufl.edu/users/gbowes/bot3503/psdkrx.html) If the optimum pH is 8.2 then pHs significantly higher or lower will affect (denature) the enzyme and therefore the rate of photosynthesis. If the rate of photosynthesis slows down it will decrease the rate of production of glucose, amino acids and lipids. This will decrease the growth rate of the plant. Enzymes: Enzymes can be described as biological catalysts as they catalyse (speed up without changing) almost every metabolic reaction. A factor affecting the ability of enzymes to fulfil their potential is pH. Different enzymes work best at different pHs, for example, pepsin works best in the acidic environment of the stomach. Each enzyme has an optimum pH and extreme changes can cause a change in the ionisation state of the amino acid side chains in the enzyme molecules and therefore a change in the ionic bonds within the tertiary structure of the enzyme (protein molecule) creating a change in the shape of the molecule and its active sites, inhibiting the action of the enzymes on the original substrate by rendering them unable to bind with the substrate molecules. Enzymes are globular proteins, meaning they are protein molecules (chains of amino acids) coiled into specific 3 dimensional shapes, creating their distinguishing feature, the active site. This site is a particular shape to which the targeted substrate can bind, formed by the bonding of various groups along the amino acid chain (ionic bonds, disulphide bonds, hydrogen bonds and hydrophobic bonds). This is called the lock and key principle and is one theory of how an enzyme works. Another theory is the induced fit model. This puts forward that the walls of the active site move a little to wrap around the substrate, this stretching putting stress on the active site and the bonds within the substrate making them weaker and therefore lowering the activation energy for the reaction. Apart from pH, enzymes are affected by a number of other factors, including temperature because if too cold they do not have enough energy to collide with their substrate or enough activation for it to be a successful collision, if too hot then the enzymes denature as the hydrogen bonds within the active site break, changing the shape of the molecule. Respiration:

6CO2 + C6H12O6 6CO2 + 6H2O

Respiration relies on the use of enzymes to catalyse the metabolic reactions taking place. Through the process of respiration plants gain their energy used for, among other things, growth.


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It is the Krebs cycle and oxidative phosphorylation which, massively rely on the action of enzymes. During oxidative phosphorylation an electron carrier chain made of cyctochrome (protein molecules) transports electrons down various energy levels to eventually be received by an oxygen molecule. During the Krebs cycle, Acetyl co-enzyme A (ACoA) is combined with a 4 carbon acid to form a 6 carbon acid which is converted (via a series of enzyme controlled reactions, through various intermediates) to Oxaloacetate and eventually back to a four carbon acid which combines with another ACoA to complete the cycle. The protein molecules would be affected by a change in pH, altering their three dimensional structure, leading to an interruption of the electron transport chain and therefore (due to a feedback system) the whole of aerobic respiration.

Hypothesis: The growth of pea plants will be affected by differing pHs (measured by the average length of shoot (of three plants) and by the dry masses of each plant). The greatest amount of growth will occur at pH7 and the least amount will occur at the two extremes, pH2 and pH10.

Null hypothesis: There will be no difference in the growth of the pea plants at different pHs and any difference will be due to chance only.

Method: Eight plant pots were filled with compost and three pea plants (each seed from the same

female parent plant) were placed an equal distance apart from each other and the sides of each pot.

The eight plant pots were then labelled pH2, pH3, pH4, pH5, pH6, pH7, pH9 and pH10. A mixture of 20cm3 of the corresponding acidic solution/distilled water was distributed

as evenly as possible (to make sure each plant is receiving the same amount of water also using a measuring cylinder) over the three seeds in each pot,

The eight plant pots were then placed in the same greenhouse making sure they are all receiving the same amount of light and are not shadowed by other objects.

Over the next four weeks all the plant pots were watered with distilled water at the same time as each other (when they looked as though they needed water) with the same amount to each (10cm3). At various intervals during the weeks, the pea plants/shoots were measured and the

data recorded on a table. Every seven days each plant pot was given 10cm3 of the corresponding acidic solution. At the end of the four weeks the plants were carefully removed from the pots and the

soil was washed away with a gently running tap. The wet weights of each plant was taken the plants were then placed in a pre-weighed

crucible and the crucibles were placed in a drying oven for 24 hours and then re-weighed.

The values were then compared, length of shoot/plant and wet and dry masses at each pH.

Extraneous variables: The genetic make up of each pea plant cannot be controlled so that they are each exactly the same (unless each pea was a clone of one original pea). So difference in height of the pea plants may be purely due to the fact that one plant had the genetic makeup coding for it to be short and therefore nothing to do with the varying pHs.


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Controls: The temperature and amount of light exposure was the same for each plant pot as they

were all kept in the same greenhouse on an open shelf where they didnt experience and shadowing from other plants.

The amount of water given to each plant pot was the same (10cm3). The volume of acidic solution given to each plant pot was the same (10cm3 each week). The amount of nutrients the plants received was kept the same by using the same

compost (vermiculite) and the same amount was used in each plant pot. All the peas came from the same parent plants to make them as genetically similar as

possible. Three pea plants were grown at each different pH so as to allow for varying effects of

the different genetic make-up of the plant. Each plant was watered and measured at the same time. The distance apart from each other and the sides of the plant pot was the same for

each plant (as far as possible) so that each pea plant had the same amount of space in which to grow and were also therefore competing for the same amount of as each other.

Each pea plant pot was grown for the same amount of time i.e. four weeks. Safety precautions: As the experiment involved dealing with an acid, care was taken when handling the acid

and eye protection was worn. Total: 4/8

Moderators comments

Strand (a) the student had a clear plan of action but some details were not considered or carried out. For example, the layout of the plants in the greenhouse should have been randomised, vermiculite is described as a compost and volume should have been used instead of amount.

Strand (b) one relevant safety precaution is stated. This experiment does not have major hazards but a little more might have been added.

Strand (c) there is no record of a trial experiment. In order to gain higher marks the student would need to:

report the trial experiment increase the number of pea plants given each treatment obtain more performance data from the pea plants, such as leaf length or leaf

area, as evidence of good attention to detail.


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Exemplar 4 Robyns work

An Investigation into the Anti-bacterial Properties of Allicin supplements.

Abstract: This experiment was done in order to investigate the antibacterial properties of garlics active ingredient, allicin. It was also to see if allicin could work in synergism with the antibiotic streptomycin. It was found that at low and high concentrations allicin inhibits the antibiotic and then at high concentrations is starts to have its own anti-bacterial effect. Research and Rationale: It has long been believed that garlic is good for colds and general sickness; I decided to make the aim of my investigation to determine if allicin, garlics active ingredient, has any anti-bacterial properties. I found a supplement that is 100% allicin and its website [see bibliography] claims ALLIMAX may be used to reduce symptoms of bacterial infections and also kills E. coli. A garlic supplement is often recommended by herbalists as a supplement worth taking whilst on antibiotics, so this investigation is seeing if there is any truth in this. Garlic [Allium sativum]; produces allicin when its injured through an enzyme based reaction possibly to protect itself from insects and fungi. Allicin is known as 2-propene-1-sulfinothoic acid S-2-propenyl ester; thio-2-proene-1-sulfinic acid S-allyl ester. The enzyme, alliinase, is stored in separate compartments to the compound alliin in garlic. When its damaged the two combine and produce allicin:

[picture from: www.allicin.com] Allicin is theorised to destabilise enzymes that are used by bacteria to infect the body by attacking their active sites particularly the sulphydral groups by forming disulphide bridges. [See bibliography from information source]

Bacterial cell walls contain a unique material called peptidoglycan, this is made of polymers of modified sugars cross-linked by short polypeptides that vary with species, a build up of peptidoglycan results in a single laminated structure that encloses and protects the bacterial cell from attack. The aminoglycoside antibiotic used in this investigation is Streptomycin which works by entering through the bacterial cell through an oligopeptide transport system in its membrane. Once inside the cell it prevents the two units of a ribosome from joining together, and therefore preventing protein synthesis.


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[picture from website (see bibliography)] The aminogycoside, in this case streptomycin, prevents the larger part of the ribosome from joining onto the smaller and therefore engaging in protein synthesis. [see bibliography for information source] Allicin is highly unstable and quickly changes into other products. ALLIMAX is a one-a-day supplement that contains 180mg of allicin in each capsule. As allicin is meant to be a supplement I decided to test it with an antibiotic, to see if allicin aided antibiotics works better than antibiotics alone. The best agar after testing with 3 drops of E.coli spread on each with aseptic technique [see appendix note i] I found to be Nutrient Agar. Planning Preliminary: My first plan was to dissolve the allicin capsules in water with pepsin to break down the actual capsules. 2 molar hydrochloric acid was added to simulate the acidic stomach conditi

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