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"An investigation into the Respiration of Carbohydrate Substrates by Yeast."

Extracts from this document...

Introduction

AS Biology Coursework 2004. Lucy Nuttney "An investigation into the Respiration of Carbohydrate Substrates by Yeast." Abstract. The investigation considered the reactivity of respiration of three different carbohydrate substrates; glucose, sucrose and starch, by two different sub-species of saccharomyces cerevisiae yeast. The rate of reaction was measured by collecting volumes of gas in a displacement reaction at standardised conditions e.g. time, temperature, pressure, volume of yeast/ sugar. Results showed that glucose produced the most carbon dioxide, followed by sucrose then starch, the biggest difference being between sucrose and starch. Baker's yeast had a slightly higher average than brewer's yeast but it was not considered to be a significant difference and therefore could have been due to chance. It was concluded that both yeasts respire glucose and sucrose at insignificantly different rates but the difference between starch is much larger and therefore much more significant. Pilot Experiment. Before we could test which carbohydrate and type of yeast produced more carbon dioxide, we had to standardise the other variables of this experiment; temperature and concentration. Therefore, in order to find the optimum conditions we carried out a pilot experiment. In this experiment we used a range of temperatures from 10� to 60�C and three different concentrations of carbohydrate 1%, 5% and 10%. The experiment was carried out as a group experiment with everyone being allocated a different temperature and concentration to test. It was carried out over a standardised period of 5 minutes. The rationale for conducting this pilot experiment was that enzymes are biological catalysts that are made up of globular proteins which are activated to work by temperature. They exist in the yeast and our bodies and therefore work best at 40�C, however, they denature soon after and so our body temperature is kept at 37�C to ensure this does not happen. Denaturation is the irreversible loss of 3D structure of enzymes and can be caused by excess heat or a change in PH. ...read more.

Middle

Control of the measurements When taking measurements, the following points should be noted: -When measuring the gas, measure to the bottom of the meniscus of the water. -Make sure the measuring cylinder is perpendicular to the clamp stand to ensure that the water lies at the correct level. -When timing, do not shake at 30 seconds by the stopwatch because 5 seconds is added on each time (while it is shaken) and therefore by the sixth minute or so it will require shaking as soon as it has been shaken. -Keep a constant check on the thermometer to ensure the temperature does not drop. Safety Risk Hazard Prevention In case of accident Bunsen Burner Could burn yourself/ keep all loose clothing Put out fire if possible cause a fire /hair tucked in/tied to do safely, alert a back teacher. Rinse any minor burns under cold tap. Glass Could smash and you Handle glass with care. Sweep up broken could cut yourself. Do not run cold water glass with a dust onto hot surface of pan and brush and glass as this could inform a teacher of cause it to shatter. any injury sustained. Spillages Someone could slip Clean up all spills. Alert teacher and fall over. Work away from immediately. The water could get electrical supplies. Plug sockets and Cause an electric Shock. Results. A summary table to show volume of gas produced by bakers and brewers yeast with three different carbohydrate substrates. Amount of CO2 produced in cm3 in fifteen minutes in each condition The table above shows the results of our practical, including my own, highlighted in blue. The average volume of gas collected in each separate condition is shown and reveals that most gas was produced in the brewer's glucose experiment, at 115.6 cm3 and the condition that produced the lowest average was brewer's starch, at 9.4. The range of the averages was 94.3, showing there was a large difference between the values. ...read more.

Conclusion

We could test different species of yeast or different carbohydrates against each other eg. Glucose v. fructose (monosaccharides), sucrose v. maltose (disaccharides) and starch v. cellulose (polysaccharides) to see if there was any difference. Another condition that could be tested is PH as enzymes are also affected by this and therefore we could attempt to find the optimum PH for this reaction. Conclusion. In conclusion to this experiment, our first hypothesis of 'When respired by yeast, different types of carbohydrates will produce different amounts of CO2,' was accepted as the results between carbohydrates were all highly significant except for baker's glucose and sucrose, though there was still a difference. Therefore we can reject our first null hypothesis of 'The type of carbohydrate being respired will have no significant effect on the amount of carbon dioxide produced in a given time.' Our second hypothesis of 'Different types of yeast will produce different volumes of CO2,' was refuted in two cases but accepted as being significant when comparing brewer's and baker's starch. We can therefore partially accept our null hypothesis of 'There will be no significant difference between the amount of carbon dioxide produced by the Baker's and the Brewer's yeast.' Bibliography As research for my report I used the following books: 'Advanced sciences Biology 1' by OCR. I also used classroom notes from the teacher and the following internet sites: www.coursework.info www.courseworkbank.co.uk Acknowledgements. Mrs Coulter, the technician helped us with our experiment by setting up electronic water baths to preheat the yeast in. Contents Front cover.................................................................................................... Pg 1 Abstract......................................................................................................... Pg 2 Pilot Experiment........................................................................................... Pg 2-6 -Aim................................................................................................................. Pg 2 -Apparatus..................................................................................................... Pg 2 -Diagram......................................................................................................... Pg 2 -Procedure..................................................................................................... Pg 2-3 -Results for the pilot experiment........................................................... Pg 4 -Analysis of results..................................................................................... Pg 4-5 -Limitations/ modifications from the pilot........................................... Pg 5-6 Introduction.................................................................................................. Pg 6-8 -Aim................................................................................................................. Pg 8 -Hypotheses.................................................................................................. Pg 8-9 Main Method................................................................................................. Pg 9-11 -Apparatus.................................................................................................... Pg 9 -Diagram........................................................................................................ Pg 9 -Procedure.................................................................................................... Pg 9-10 -Control of the variables of the method............................................... Pg 10 -Control of the measurements................................................................. Pg 10 -Safety........................................................................................................... Pg 11 Results........................................................................................................... Pg 12-18 -Analysis of results. .................................................................................. Pg 13 -T test........................................................................................................... Pg 13-18 Discussion..................................................................................................... Pg 18-20 Conclusion..................................................................................................... ...read more.

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Response to the question

An outstanding piece of A level coursework. Every possible aspect has been covered in great detail and answers the question with a large amount of breadth regarding the optimum conditions for yeast respiration, the theories that support this e.g. collision ...

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Response to the question

An outstanding piece of A level coursework. Every possible aspect has been covered in great detail and answers the question with a large amount of breadth regarding the optimum conditions for yeast respiration, the theories that support this e.g. collision theory, and some other areas of the biology curriculum such as organism classification. It is vital to include as much breadth from other parts of the syllabus as you can to ensure you will achieve high grades. I would suggest that writing something this detailed is not necessary for achieving the top grades but it would definitely be beneficial to take some suggestions regarding the layout of the investigation, beginning with an abstract, which is a standard of university level study and research, and clearly separating the pilot and primary investigations into their respective hypotheses, introductions and procedures etc. In addition, statistical analysis is always something that will impress examiners as it is something new that is introduced by the A level course and this piece gives examples of some of the major ones such as finding the significant difference between data and therefore being able to objectively assess obtained results rather than just assuming whether the results are due to chance or a scientific process. This sort of thing is always going to impress markers, but try and make sure your results are displayed clearly and explained, this piece can sometimes be hard to follow due to the sheer quantity of data.

Level of analysis

As I’ve mentioned, this coursework demonstrates excellent detail of analysis, clearly covering the rate of reaction and carbohydrates portion of A level Biology, bringing in knowledge of the respiration reaction through equations. At this level, using knowledge of biochemistry and statistics is going to impress examiners if done well as it demonstrates you deeply understand the mechanisms of reactions and can effectively assess those using accurate mathematical methods rather than just copy down facts from a textbook. The excellent discussion at the end covers evaluation as well as linking the scientific basis of the reaction to the results, however I think it is best to have a separate discussion, evaluation and conclusion to avoid confusion and maintain clarity.

Quality of writing

This piece appears to have no real errors in spelling or grammar and as a result communicates its ideas reasonably well, I think the issue here could be with the multiple experiments and making sure that results and analysis are not interchanged accidentally between them, but for a modern A level investigation this shouldn’t be an issue as you typically only go into detail about the main experiment. Always keep your writing clear and concise.


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