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TAS Training Workshop for A-level Biology Teachers

2. General guideline for Assessment. Refer to TAS handbook (2009 AL Exam) . 3. Easy way to prepare checklist. Add some points which are important in the experiment in the general guideline stated in the handbook. . 4. Importance of preparing simple checklist. Preparation of a simple checklist is a good way of pre-lab..

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TAS Training Workshop for A-level Biology Teachers

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    1. 1 TAS Training Workshop for A-level Biology Teachers Sharing of experience in marking Area B

    2. 2 General guideline for Assessment Refer to TAS handbook (2009 AL Exam)

    3. 3 Easy way to prepare checklist Add some points which are important in the experiment in the general guideline stated in the handbook.

    4. 4 Importance of preparing simple checklist Preparation of a simple checklist is a good way of pre-lab.

    5. 5 General point to be notice in Area B marking (15 min)

    6. 6 Area B1 2 main parts should be considered (1) Experiment design (2) Procedure

    7. 7 (1) Experiment design Apply the knowledge of biological principle to the design of the investigation NOT to state the theory of the experiment and NOT to state the detail procedure.

    8. 8 Example of writing experiment design e.g. Investigation: To determine the solute potential of epidermal cells of Rhoeo discolor Based on the biological knowledge ?=?s +?p, design an experiment to find the solute potential of the epidermal cells To immerse the epidermis into different concentrations of sucrose solution. Water moves in or out due to the water potential difference between the epidermal cells and the surrounding solution. At the concentration of surrounding solution that causes the incipient plasmolysis, the solute potential of the epidermal cell is equal to the water potential of the epidermal cell because the pressure potential becomes zero. At this equilibrium state, the water potential of the epidermal cell is equal to the water potential of the surrounding solution. Therefore, the solute potential of the epidermal cell is equivalent to the water potential (or solute potential) of the surrounding solution. Such solute potential is expressed in the terms of concentration of solution in this experiment.

    9. 9 Assumption Based on the assumption, the experiment can work. e.g. Action of amylase on starch Assumption: failure to produce blue black colour indicates the disappearance of starch. (Actually, small amount of starch is still present) e.g. To determine the solute potential of cell sap in plant epidermal cells Assumption: (1) cells in different epidermal cells are similar (actually, it is not) (2) all cells reach equilibrium with the surrounding solution when they are observed under the microscope. (3) solute potential of epidermal cells does not change during the treatment. (Actually it changes as water enters or leaves the epidermal cell)

    10. 10 Variables State different kinds of variables, if any Independent variables Dependent variables Controlled variables

    11. 11 (2) Procedure Based on the principle of experiment design, write the steps logically. Basic calculation principle should be mentioned to indicate the conversion of raw data into presentable data. Including precaution State the exact time period in treatment, exact volume of solution used, exact temperature in treatment etc.

    12. 12 Area B2 1. Tabulated result : Notice the position of independent variable, dependent variable in the table. Units and suitable conversions should be shown clearly and correctly Title of the table should be written correctly according to the aim of the experiment. e.g. Effect on sucrose concentration on the length of potato cylinder.

    13. 13 Effect of sucrose conc on the percentage change in length of potato tuber

    14. 14 2. Plotting graph Notice choice of axes x-axis – for independent variable (unit should be stated) y-axis – for dependent variable (unit should be stated) Notice the rule how to use short-straight line to join the points or the smooth curve to join the points. Title for the graph should be added correctly and related to the aim of experiment. e.g. Effect on sucrose concentration on the % change in length of potato cylinder.

    15. 15 3. Calculation: Sometimes, calculation is needed e.g. calculate the reaction rate; such data should be written in the tabulated result. e.g. calculation of % of plasmoylsed cells the results should be filled in the tabulated result. The rule of calculation should be already stated in the principle of experiment design or in the procedure.

    16. 16 Area B3 The weakest part in students’ report (esp. in the first semester of F.6)

    17. 17 1. Interpretation of data Refer to the graph, state the trend and pattern, explain why it happens (based on the knowledge learnt in lessons) The interpretation of data should be related to the aim of the experiment and it can deduce to draw the conclusion.

    18. 18 2. Limitation of method, sources of error (esp. inevitable errors) e.g. counting under microscope may lead to counting error e.g. determine the amount of ppt by arbitrary method e.g. determine vit. C in grape – it cannot decolorize DCPIP into colourless - difficult to determine the amount of grape juice used in decolorizing DCPIP e.g. determine the end point of disappearance of starch – which pale brown colour is used as the reference for the disappearance of starch

    19. 19 3. Any improvement to reduce the above source of errors. (Try to state the method and it should be related to the aim of the experiment. The suggested method have to be able to be carried out) Can we use light sensor to determine the turbidity of solution due to the formation of ppt in reducing sugar test / The colour of the end point in iodine test ?

    20. 20 4. Further investigation (e.g. application to daily life) e.g. Experiment: study the temperature effect on the activities of amylase. “To study the temperature effect on the action of protease.” is not a good example of the further investigation. “ To study the temperature effect on the enzymes in hot spring bacteria” – How about it ? e.g. Experiment: To determine the vitamin C content in lemon juice. “To determine the vit C content in apple juice” is not a good example as the further investigation. “ Study the temperature effect on the vitamin C content in lemon juice ?” – How about it ? “Compare the amount of vitamin C in different kinds of fruit juice” – How about it ?

    21. 21 5. Conclusion - a summary on the experiment results. It should be related to the aim of the experiment or the hypothesis set at the beginning of the experiment. Use one or two sentences only. No explanation is needed (because the explanation should have been stated in the interpretation of results.). Sometimes, if the argument is very strong and it is not appropriate to put in the interpretation of results, the argument should be written here to support the conclusion

    22. 22 Sharing of rationale in marking students’ reports (15 min) A. Determination of solute potential of epidermal cells of Rhoeo discolour Student report 1 and student report 2 B. To identify the unknown solution Student report 3 and student report 4

    23. 23 Practice (30 min) Divide into 4 groups use the attached brief checklist to mark the HKEAA exemplar IB and IC. Please choose a secretary in each group to jot down the rationales.

    24. 24 Reporting of marking and discussion (10- 20 min)

    25. 25 Thank you !!!

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