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Biology AS Assessed practical: Mitosis

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Introduction

Biology AS Assessed practical: Mitosis Risk assessment for practical * Wear safety goggles when handling chemicals, such as hydrochloric acid and acetic orcein stain, to prevent any foreign particles from entering the eye, as if acetic orcein stain is overheated it tends to bubble and spit. * Take care when handling the Bunsen burner as you may burn yourself. * Tie your hair back if it is long to prevent it catching alight when using the Bunsen burner, and to prevent it from restricting vision by getting in your eyes. * Take care when handling the acetic orcein stain as if spilled it will stain clothing and skin. * Do not sit down during the experiment, especially when Bunsen burners are alight, and keep all chairs/stools out of the way as these will slow down reaction time, in case of an emergency. * Take care when using the scalpel as it is sharp and you may cut yourself, and always use a wooden board to ensure you do not make incisions elsewhere. Results Table of class results showing the averages for the number of cells out of 50 undergoing each stage of mitosis. ...read more.

Middle

I converted the figures into the expected ratios from the angles in the pie chart occupied by each phase of mitosis by calculating each angle and dividing by the overall sum of the angles, e.g. for prophase the angle was 25? and I divided this by 71? as this was the sum of all the angles I calculated. Then using these figures I divided each answer by the smallest number I had calculated to give me the ratio of cells between each phase of mitosis. I divided each ratio by the total of the ratios and multiplied by 50 (the number of cells observed) to give me the expected number of cells from 50 in each stage of mitosis. Diagram summarising the events of the cell cycle. Table showing the expected number of cells from 50 cells. Data taken from diagram above. Stage of mitosis Angles in the pie chart occupied by each phase, expressed as a fraction of the overall angle of nuclear division by mitosis Ratio of cells between each phase of mitosis Expected number of cells from 50 in each stage of mitosis Prophase 25/71 0.3521 18 Metaphase 18/71 0.2535 13 Anaphase 13/71 0.1831 9 Telophase 15/71 0.2113 11 This ratio is different from the one I used earlier, but ...read more.

Conclusion

This could have been due to errors such as: > Human error- this can result from individual interpretations of the slides. This can be overcome by allocating one person to interpret the number of cells in each stage of mitosis. Also anomalies may occur due to individuals counting the same cell twice. > Variation between the slides- variations between each root tip can cause an increase when the results are pooled together as each individual may examine a different area of the root tip where there may be different number of cells undergoing mitotic division. > Incorrect preparation of the slides- this can occur by using incorrect measurements of hydrochloric acid and acetic orcein stain, if too much stain is used it is difficult to identify the cells, and also over heating the tips damages them. These errors can only be avoided by taking the necessary precautions. If I had to repeat this experiment I would modify it to increase reliability and this can be achieved by minimising errors listed above. Allocating one person to identify the cells, following the method as accurately as possible and using a larger number of cells would all improve the validity of the results and conclusions drawn. ...read more.

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