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AS/A2 AQA Biology and Human Biology

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  • ‘ students statistics sheet’ will be version 2
  • Transcript

    • 1. Reflections on Practical Assessment and Improving Student Outcomes
    • 2.  
    • 3.
      • ISA is teacher-assessed (Route T)
      • - using marking guidelines
      • - issued with ISA so guidelines do not change
      • EMPA is board-marked (Route X)
      • - using mark scheme
      • - can be modified to take account of
      • student responses
    • 4.
      • Both include:
      • A Task ( Stage 1 of ISA)
      • Collection of data and production of a table
      • Processing of data (normally) and production of a graph (AS) or statistical treatment (A2)
      • A Written Test
    • 5.
      • Both require that a centre:
      • has the relevant materials and equipment available
      • carries out trial investigations
      • consults their Assessment Adviser if there are difficulties or issues arising from a trial
    • 6.
      • ISA requires assessment of Practical Skills (PSA) – 6 marks
      • EMPA only requires verification (PSV) – no marks (but verification must be given)
      • EMPA has Task 1 and Task 2
      • Distribution of marks is slightly different
    • 7.
      • Both have ISA and EMPA route
      • AS unit 3 and A2 unit 6 have 50 raw marks (60 UMS)
      • All marks in Human Biology EMPA are matched to a specific point but some reflect quality of data
      • Biology EMPA attributes up to 3 marks for ‘Quality of data’ collected by candidate
      • Assessment of tables, processing and statistics follows the same pattern
      • Slight differences with distribution of marks
    • 8.
      • Provide a resource bank of:
      • practical investigations relevant to both specifications
      • questions testing
      • - understanding of terms used in examination papers
      • - appreciation of ‘how science works’ terminology
      • - investigative and practical skills
      • - mathematical skills
      • Resource sheets for comprehension exercises
    • 9.
      • Is a preliminary investigation
      • Has written questions associated with it
      • Typically worth 8 marks (Biology) or 10 marks (Human Biology)
      • Replaces PSA marks with remainder from other stages of EMPA
      • Emphasis on quality of data (with loss of PSA)
    • 10.
      • Format of Tasks and Written Tests are essentially the same
      • Both Written Tests have Section A and B
      • Section A based on candidate’s investigation and results with associated theory
      • Section B based on material in Resource Sheets i.e. investigations of other people (which are not always ‘perfect’)
      • ISA Written Test has (a few) more marks
      • (but same time length as EMPA)
    • 11.
      • Two ISA opportunities in any one year
      • One EMPA opportunity per year
      • At least 3 sessions needed per ISA
      • At least 4 sessions needed for the EMPA
      • Time for two ISAs? (and two trials?)
      • Previous years ISAs/EMPAs (and Specimen Material?) provide practice opportunities within a course programme
      • - as part of practical work
      • - as part of homework
    • 12.
      • PSA requires several assessments (to represent true ability) and provide a record of marks
      • ISA marking requires appreciation and application of marking guidelines
      • ISA requires internal standardisation where more than one assessor
      • Marking of ISA is moderated (and subject to a tolerance level)
      • ISA marks of centre can be regressed
      • Separate awarding
      • Students who miss ISA opportunities could take EMPA (later in calendar)
    • 13.
      • Differences between centres in marking the ISA
      • Differences between teachers within a centre in marking the ISA
      • Different standard of applying marking guidelines by an individual teacher across candidates
      • Teachers ”know what their students meant” so give credit where the answer is incomplete
      • Teachers (in some centres) credit what else they think is “valid” but not in the marking guidelines
      • Moderator feedback forms part of appraisal?
    • 14.
      • It seems that
      • candidate entry is about two thirds for ISA and one third for EMPA
      • there is an approximate equal split between which of the two ISAs is submitted
      • the ability range is similar for both routes
      • the outcome of the two routes is similar
    • 15. Year (entry) A* A B C D E U 2009 AQA AS Biology (26361) 17.2 34.0 52.2 68.2 81.1 100.0 National AS Biology 18.6 35.5 53.3 69.3 82.6 100.0 2010 AQA AS Biology (32672) 18.9 36.4 54.7 71.0 83.9 100.0 National AS Biology (83408) 18.7 36.4 54.3 70.3 83.6 100.0 AQA A level Biology (23295) 8.8 29.4 52.5 73.1 88.2 97.2 100.0 National A Level Biology (55485) 8.0 28.5 51.7 72.4 87.6 96.8 100.0
    • 16. A* A B C D E U A level Human 2009 13.1 34.4 57.0 77.3 92.9 100 2010 3.0 11.8 31.2 54.6 77.5 93.4 100 A level Biology 2010 8.8 29.4 52.5 72.1 88.2 97.2 100 National A level 2010 8.0 28.5 51.7 72.4 87.6 96.8 100 AS Human 2009 7.5 18.3 35.6 53.9 69.1 100 2010 8.8 21.0 40.7 57.0 73.1 100
    • 17. Session Unit Max A* A B C D E Jan 2009 1 60 37 32 27 23 19 June 2009 1 60 40 35 30 26 22 .. 2 85 55 49 43 37 32 .. 3T 50 38 35 32 29 27 .. 3X 50 33 30 27 25 23 Jan 2010 1 60 38 33 27 23 19 .. 2 85 52 46 41 36 31 .. 4 75 41 37 33 29 26 June 2010 1 60 45 40 35 30 25 .. 2 85 59 52 45 39 33 .. 3T 50 39 36 33 30 28 .. 3X 50 31 28 25 22 20 .. 4 75 39 35 31 27 23 19 .. 5 100 69 62 55 49 43 37 .. 6T 50 42 39 36 33 31 29 .. 6X 50 34 31 28 25 23 21
    • 18. Unit Unit total A* A B C D E 1 80 49 44 39 34 30 2 80 58 52 46 41 36 3T 50 40 37 34 32 30 3X 50 33 30 27 24 22 4 90 67 62 57 52 47 43 5 90 70 65 60 55 50 46 6T 50 42 39 36 33 30 27 6X 50 37 34 31 29 27 25
    • 19.  
    • 20.
      • Molecule
      • Ion
      • Compound
      • Element
      • Isomer
      • Isotope
      • Bond
      • Oxidation
      • Reduction
      • Hydrolysis
      • Condensation
      • Wavelength
    • 21.
      • Use practical worksheets
      • - to follow instructions (without assistance)
      • Programme of practical work includes the use of a wide range of apparatus
      • - for selection of appropriate equipment, skillful use and accurate measurements
      • Risks and hazards recognised
      • - to promote safe working
    • 22.
      • Are all the designated practical activities attempted?
      • Are all the ‘Practical and Investigative Skills’ covered by the programme of practical work?
      • Are students familiar with principles of ‘How Science Works’
      • Have ‘Mathematical Requirements’ been addressed or are they assumed to be in place from GCSE?
    • 23.
      • … .questions on practical technique could appear in other unit examination papers
      • … .‘How Science Works’ does appear in other unit examination papers
      • … .candidates often fail to achieve marks available for calculations
      • … .many fail to explain mathematical concepts appropriately.
    • 24.  
    • 25.
      • Biochemical tests
      • - biuret test for proteins
      • - use of Benedict’s reagent for reducing sugars and non-reducing sugars
      • - iodine in potassium iodide for starch
      • - emulsion test for lipids
      • Enzymes
      • - effect of specific variable on rate of reaction of an enzyme-controlled reaction
      • Exercise
      • - effect of a specific variable on human heart rate or pulse rate
      • Water potential
      • - effect of solute concentration on the rate of uptake of water by plant tissue
    • 26.
      • Use of an optical microscope
      • - to observe the structure of a palisade cell from a leaf
      • - preparing temporary mounts (of plant cells,
      • tissues or organs)
      • - staining
      • - estimation of size
      • Ecology
      • - collection of data relating to intraspecific variation
      • Transpiration
      • - measurement of the rate of water uptake by means of a simple potometer
    • 27.
      • Biochemical tests
      • - use of Benedict’s reagent for reducing sugars and non-reducing sugars
      • - iodine in potassium iodide for starch
      • Enzymes
      • - effect of pH and temperature on rate of enzyme-controlled reaction
      • Water potential and osmosis
      • Chromatography and calculation of Rf values
      • Use of sterile technique and bacterial growth on agar plates
    • 28.
      • Use of an optical microscope
      • - preparing temporary mounts
      • - staining
      • - estimation of size
      • Exercise
      • - changes in heart rate
      • - changes in ventilation
      • Mitosis
      • - observation of stages
    • 29. and how could they be incorporated?
    • 30.
      • Skill
      • Use of water baths to change or control temperature
      • The use of buffers to change or control pH
      • Production of a dilution series from a stock solution
      • Quantitative v qualitative
      • Practical ?
      • - Enzyme investigation
      • - Enzyme investigation
      • Dilution of Benedict’s or substrate (for enzyme)
      • - Colour of solution by eye or colorimeter
    • 31.
      • Skill
      • Collection of data where
      • - gas is evolved
      • - colour change occurs
      • - mass or length changes
      • Practical?
      • - Catalase
      • - Benedict’s reagent with glucose concentrations
      • - Water potential of potato
    • 32.  
    • 33.
      • Page 45 of biology specification
      • Page 43 of human biology specification
      • It is expected candidates will need……
      • “…… to have been taught, and to have acquired competence in, the areas of mathematics set out…….”
    • 34.
      • use ratios, fractions and percentages
      • make estimates of the results of a calculation (without using a calculator)
      • use calculators to find and use mean, standard deviations, square root and x n , 1 / x , √ x
      • understand the principles of sampling as applied to biological data
      • understand the terms mean, median and mode and standard deviation
      • use a scatter diagram to identify positive and negative correlation between two variables
    • 35.
      • change the subject of an equation
      • understand the use of logarithms……
      • calculate the rate of change from a graph showing a linear relationship
      • draw and use the slope of a tangent to a curve as a measure of rate of change
      • calculate circumference and areas of circles, surface areas and volumes of rectangular blocks and cylinders when provided with appropriate formulae
    • 36. To help you process your data, the time required for each stage of the cell cycle can be calculated using the formula: Number of minutes = number of cells in stage x 720 to complete a stage total number of cells counted Stage Number of cells Time in each stage Interphase 177 504 Prophase 4 7.2 Metaphase 7 14.4 Anaphase 1 2880 Telophase 63 180
    • 37. Stage of mitosis Number of cells in stage of mitosis Percentage of cells in stage of mitosis Time to complete stage of mitosis / minutes Prophase 108 0.74 72.9 Metaphase 16 5 21.6 Anaphase 8 10 13.5 Telophase 28 2.86 3.85
    • 38. A scientist studying onion root tips found that the time taken for mitosis was about 80 minutes . She recognised that the proportion of 80 minutes that a stage of mitosis took to complete could be found from the percentage of cells in that stage of mitosis. She used this to calculate the time in minutes for each stage of mitosis. Use the scientist’s method to complete the table. Stage of mitosis Number of cells in stage of mitosis Percentage of cells in stage of mitosis Time to complete stage of mitosis / minutes Prophase 108 112.5 54 Metaphase 16 10 8 Anaphase 8 5 4 Telophase 28 17.5 14
    • 39.
      • Know the Institute of Biology conventions
      • - n.b. 3 rd edition (2000)
      • - column heading requires a full description of variable
      • - independent variable in the first column
      • - units only in headings
      • - units do not change / are not mixed
      • - unit separated from the variable by a solidus (but brackets accepted)
      • - a title is good practice (but not assessed as such) because it can help an incomplete heading
    • 40.
      • Investigation example
      • produces data of time taken for pH indicator to turn blue following exposure of respiring bacteria to different temperatures
      • - worksheet
    • 41. Table 1 Temperature ( o C) Test 1 Test 2 Test 3 Average (m) Colour Time (m) Colour Time (m) Colour Time (m) 20 Blue 3.20 Blue 1.55 Blue 2.50 2.41 30 Blue 2.53 Blue 3.06 Blue 4.09 3.22 40 Blue 1.26 Blue 2.35 Blue 2.20 1.93 50 Blue 1.46 Blue 1.02 Blue 0.45 0.97 60 Blue 0.60 Blue 1.25 Blue 2.26 1.37
    • 42. Table 2 ‘ Effect of temperature on time taken to change colour’ Time (s) Average (s) Temp o C Tube 1 Tube 2 Tube 3 20 193 159 171 174 30 128 131 176 145 40 91 82 117 97 50 97 103 120 107 60 260 317 302 293
    • 43. Table 3 Test tube Temperature of water bath Time taken to turn blue Repeat time taken to turn blue Average 1 20 o C 7 minutes 15 seconds 7 minutes 11 seconds 7 minutes 13 seconds 2 30 o C 2 minutes 1 minute 45 seconds 1 minute 52.5 seconds 3 40 o C 36 seconds 47 seconds 41.5 seconds 4 50 o C 34 seconds 31 seconds 32.5 seconds 5 60 o C 8 minutes 57 seconds 9 minutes 33 seconds 9 minutes 15 seconds
    • 44.
      • What can students be expected to do?
      • “ Students should be able to calculate”
      • Mean
      • Standard deviation
      • Rate
      • Percentage change
      • But other calculations could be required where the formula is provided
    • 45.
      • Independent variable and dependent variables on correct axes
      • Appropriate use of scale
      • Labels on axes complete with appropriate units
      • (Mean) data plotted accurately
      • Appropriate line
      • Correct choice of line graph, bar chart, histogram or scatter diagram
    • 46.
      • IV (x-axis) and DV (y-axis)
      • Appropriate use of scale
      • - to allow accurate plotting and reading off of values
      • - scale is linear
      • - axes can start at values above zero
      • Labels of both axes complete with appropriate units
      • - a title is good practice (but not assessed as such) because it can help an incomplete label
    • 47.
      • All (mean) data plotted accurately
      • - choose a scale that is suitable for plotting
      • Appropriate line
      • - plotted points joined
      • - line of best fit is a smooth curve or a straight (ruled) line
      • - line of best fit reflects plotted data
      • - point to point (ruled) lines are acceptable
      • - no extrapolation (back to zero or beyond plotted values)
    • 48.
      • Correct choice of line graph, bar chart, histogram or scatter diagram
      • - line graph where data for both IV and DV are continuous
      • - bar chart where IV is categoric (presented as lines or blocks of equal width which do not touch) and DV is continuous
      • - histogram where IV is continuous (presented as blocks which do touch) and DV represents frequencies
      • - scatter diagram used when investigating relationship between two naturally changing variables
    • 49.
      • - worksheets
    • 50.
      • The number of marks allocated equals the number of points expected (usually 2 lines per mark)
      • Answer the question asked
      • General wording allows for a specific response e.g. “what is the effect of…” or “how would altering…”
      • Specific wording requires different language in the answer
      • Don’t add more to the answer than the question requires
    • 51.
      • Context - table shows data for fresh mass and dry masses of cucumbers before and after adding either water or liquid fertiliser to them.
      • Question – What conclusions can be drawn about the effects of using liquid fertiliser on the mass of cucumbers? (2 marks)
      • Comment – ‘effects’ and ‘mass’ are general so answer can be specific about direction of effect (increase or decrease) on type of mass (fresh or dry). Furthermore, there is the opportunity to compare extent of changes e.g. “fresh mass increased greatly but there was only a small decrease in dry mass.”
    • 52.
      • Context – tubes were left in a water bath at room temperature
      • Question - ‘Explain the advantage of using a water bath to maintain a constant temperature.’
      • What is being asked?
      • - why use a water bath? or
      • - why maintain a constant
      • temperature?
    • 53.
      • Question - ‘Describe how you would maintain a water bath at 10 o C’
      • What is being asked?
      • - why use a water bath? or
      • - how to monitor the temperature? or
      • - how to keep the water at 10 o C?
      • Suggestion - use similar examples for group work
    • 54.
      • Q ‘How are monomers joined together?’ (1)
      • A “By the process of condensation. This is the addition of a water molecule.”
      • Q ‘By what process does water pass through a partially permeable membrane?’ (1)
      • A “By osmosis because water moves from a low to high water potential.”
      • Q ‘The dye on the plastic strip did not change colour when dipped in urine. What does this show?’ (1)
      • A “That glucose was not present because the person is a diabetic.”
    • 55.
      • “ Which stage of mitosis; prophase, metaphase, anaphase or telophase, did
      • you find takes the longest time to complete?”
      • Answer: ‘ Interphase’
    • 56.
      • “ Explain the change in the mean number of metaphases over the first six hours”
      • Answer: “……..After six hours the cells……”
    • 57.
      • “ Explain the change in the mean number of metaphases over the first six hours”
      • Answer: “Over the first 6 hours numbers increase. The biggest increase was during the 4 to 6 th hour. From 0 to 6 hours the mean number has increased by 30, that means it has doubled during the 6 hours.”
    • 58.
      • Glossary for Instructions in question papers
      • - Describe
      • - Explain
      • - Suggest
      • - Evaluate
      • - Give
      • - Name
      • Glossary for How Science Works
    • 59.
      • Accurate refers to a measurement which is close to the true value .
      • Anomalous data are those measurements that fall outside the normal, or expected, range of measured values.
      • A Control experiment is one that is set up to show that the (named) independent variable is responsible for the change
    • 60.
      • Results of an investigation are Reliable if they can be repeated
      • Data are Valid if the measurements that have been made are affected by a single independent variable only
      • Conclusions are only valid if they are supported by valid and reliable data measured to an appropriate level of accuracy .
      • (One to avoid? – use of ‘fair test’ without qualification)
    • 61.
      • Why repeat an experiment or investigation?
      • - to allow anomalous data to be identified (with greater certainty)
      • - to produce a mean value that is reliable
      • Why are the sizes of pieces of potato kept the same / doses of an experimental drug given per kg body mass of patients?
      • - to allow a comparison
    • 62.
      • - worksheet
    • 63.
      • Understand what the term expects e.g. describe, explain, suggest etc.
      • ‘ Use the data’ or ‘Use a calculation to support your answer’ – so quote figures
      • What are the advantages and disadvantages…? – so give both
      • ‘ Give two reasons to….’ – giving one cannot achieve full marks
      • ‘ Give the result of your experiment…’ - “There was no change” is ambiguous but, for example, “it remained blue” is not
    • 64.
      • Anomalies present
      • Sample size small
      • Lack of replicates
      • (Identified) variables not controlled
      • Confounding variables present
      • Interpretation is subjective/judgemental/based on opinion
      • Results do not prove a causal link
    • 65.
      • General principle
      • The work of a ‘scientist’ should be considered sound. In this case the limitations would be different to an investigation carried out by ‘another student’.
      • e.g. “you don’t know if they used the same number of animals in their trials” – you would expect scientists to do so, thus it is not a limitation.
    • 66.
      • “ Urease catalyses the reaction
      • urea + water  ammonia + carbon dioxide.
      • What name is given to the type of reaction that urease catalyses?”
      • Answer ?????
    • 67.
      • Think again!
      • endothermic
      • exothermic
      • neutralisation
      • metabolism
      • hydrogen reaction
      • enzyme reaction
      • catalysation
      • oxidation
      • reduction
      • aerobic
      • build up reaction
      • decarbonisation
      • enzyme-substrate complex
      • carboxylation
      • deoxygenated
      • decarboxylation
      • chemical reaction
      • dehydration
    • 68.  
    • 69.
      • How do you teach and develop practical and investigative skills?
      • Is your practical programme formative?
      • How much practise do you give them?
      • - table production
      • - graph drawing
      • - calculations (processing)
      • Are key words re-enforced regularly?
      • - accurate / reliable / valid
    • 70. Task 1 (8) Task 2 (12) Sect A (14) Sect B (16) Example 1 2 6 5 2 4 12 10 9 2 8 8 6 2 9 6 9 2 8 5 6 3 12 7 8 2 5 6 2 Example 2 4 9 3 2 1 11 8 5 4 12 11 10 4 12 6 7 1 11 2 3 4 11 4 3 3 12 8 4
    • 71. Task 1 (10) Task 2 (10) Sect A (15) Sect B (15) Example 1 6 9 9 6 6 7 7 5 3 9 5 2 2 7 6 5 3 8 5 4 4 9 8 8 4 10 9 6 Example 2 4 4 7 8 4 6 4 4 5 9 8 4 4 6 11 7 2 6 6 2 3 8 4 1 2 4 5 1
    • 72.
      • First lesson homework
      • - draw a (line) graph
      • - feedback
      • First practical with data
      • - draw a table
      • - draw a line graph
      • - feedback
      • Subsequent work where data is collected always requires a table
      • Subsequent practical work or other activity where continuous data available always require a line graph
      • Design practical (or class activity) to generate data to plot using a bar chart. Repeat
      • Design practical (or class activity) to generate data to plot using a histogram. Repeat
      • Design practical (or class activity) to generate data to plot using a scatter diagram. Repeat
    • 73.
      • Using one task to develop and test many ideas
      • - As a class exercise or homework
      • - From a practical investigation
      • Examples….
    • 74. The table shows the respiratory minute volume (volume of air inspired per minute) of three healthy young men subjected individually to a progressive decrease in the oxygen content of their inspired air. Carbon dioxide content was held at a constant level. The RMV was calculated for each minute for 10 minutes as shown. Time / minutes 1 2 3 4 5 6 7 8 9 10 Oxygen content of inspired air / % 21 18 16 14 12 10 8 6 5 4 RMV / dm 3 per minute Man A 6.6 6.8 6.9 6.9 7.2 8.6 12.9 18.2 21.0 25.5 Man B 7.4 7.4 7.3 7.3 7.3 7.4 11.5 18.0 19.7 24.4 Man C 7.0 6.8 6.8 6.8 7.1 8.0 11.6 17.8 19.3 25.1
    • 75.  
    • 76.
      • Practical - A dilution series
      • use pipettes and e.g. a 100% glucose solution to make 10cm 3 of 80%, 60%, 40%, 20% and 0% glucose solutions.
      • Use a water bath to carry out the Benedict's test with each glucose solution.
      • As well as the practical skill (ref 3.3.1), this also enables???
    • 77.  
    • 78.
      • To see if a correlation occurs between two variables i.e. a change in one is reflected by a change in the other
      • Use when
      • - there are paired numerical data
      • - DV may have multiple values for each
      • value of IV
      • Can show positive correlation, negative correlation or no correlation
      • Care with interpretation
      • - a correlation between two variables does not
      • mean one causes the other
    • 79.
      • Require:
      • axes, labels and units
      • appropriate scales for both axes
      • the two variables for each sample plotted as a dot
      • no joining of dots
      • a title as good practice
      • - worksheet
    • 80.
      • A researcher investigated whether the weight of a person was related to
      • their height. He measured the weight and height of ten people. His results
      • are shown in the table.                                                                            
      • Use the data to draw an appropriate graph.
      • (b) How could you use the graph to predict the weight of a person whose
      • height is 140 cm.
      • Extension
      • 1 Describe the trend and suggest what this shows or
      • 2 The researcher concluded that as the height of a person increased so did
      • their weight. Evaluate this conclusion.
      Weight / kg 25 27 27 33 36 37 40 45 51 50 Height / cm 123 128 130 150 154 155 157 155 162 175
    • 81.  
    • 82.
      • Effect of pH on rate of hydrolysis of starch by amylase
      • Area of stain removed by lipases in different washing powders
      • Effect of posture on heart rate
      • Effect of salt concentration on diameter of onion rings
      • Height of all male students within the class
    • 83.
      • Percentage cover of dandelions on different football pitches
      • Frequency of blood groups within the population
      • Distribution of number of stamens per flower in a population of buttercups
      • Effect of different mineral ions on germination of lettuce seeds
    • 84.
      • Volume of water applied and yield of wheat from a field
      • Ages of runners and their times to complete 400m
      • Masses of fathers and their sons
    • 85.
      • Questions a little more demanding
      • Fewer signposts
      • ‘ In terms of water potential explain why a potato cylinder loses mass when placed in a salt solution’ – AS
      • ‘ The mass of a potato cylinder will change when placed in a salt solution. Explain how’ – A2
    • 86.
      • Task is likely to have a synoptic element
      • - practical and investigative skills from AS
      • - experience from use of apparatus and
      • techniques
      • - experience from required investigations
      • - choice of graph
      • Written Paper Section B
      • - ability to link information from several or all
      • Resources expected
    • 87.
      • ‘ A journalist wrote a column in a newspaper claiming that using liquid fertilisers improved the taste of GM cucumbers. Evaluate this statement.’ – A2
      • (final sentence for AS might read ‘Using Resources C and D, give the evidence for and against this claim.’)
    • 88.
      • Processing requires statistical treatment of data
      • - enough data
      • - null hypothesis stated
      • - appropriate statistical test chosen
      • - reasons for choice of the test
      • - calculation of test statistic made accurately
      • - test statistic interpreted
      • degrees of freedom
      • probability level
      • critical value
      • accept or reject null hypothesis
      • chance
    • 89.
      • Candidates use ‘Students’ Statistics Sheet’ provided
      • Needs a single session under controlled conditions
      • Test statistic calculated by candidates on their own
      • - computer programmes not allowed
      • - no help from teacher
      • For ISA, marked before Written Test carried out
    • 90.
      • Candidates need to be able to
      • State a null hypothesis
      • Give their choice of statistical test
      • Give reasons for their choice of statistical test
      • Calculate the test statistic
      • Interpret the test statistic (in relation to the hypothesis being tested)
      • - by accepting or rejecting the null hypothesis
      • - by using the terms probability and chance
      • e.g. there is less than a 5% probability that the differences between the results are due to chance
    • 91.
      • Independent and dependent variables:
      • The effect of soil moisture content on the abundance of dandelions in a field.
      • Null hypothesis:
      • There is no correlation between the abundance of dandelions and soil moisture content.
      • Or
      • Soil moisture content has no effect on the number of dandelions in a field.
    • 92.
      • Calculate 95% confidence limits for each sample (2 x SE)
      • Calculate
      • - (mean + confidence limit), and
      • - (mean – confidence limit), for each sample
      • Plot means and confidence limits on a graph (graph helps but is not essential)
      • See if an overlap occurs (graph makes it visual)
      Interpreting the statistical test – an example (1 )
    • 93.
      • There is no overlap of confidence limits
        • the null hypothesis is rejected
        • there is a significant difference between the means of the two samples at the 5% level of probability
        • Differences are not due to chance
      • There is an overlap of confidence limits
        • the null hypothesis is supported
        • there is no significant difference between the means of the two samples at the 5% level of probability
        • Differences are due to chance
    • 94.
      • Investigations involving looking for differences between mean values
      • - Standard error and 95% confidence limits
      • - (two sample) t test (Human Biology only)
      • Investigations involving looking for associations between different measurements from the same sample
      • - Spearman rank correlation
    • 95.
      • Investigations looking for associations between measurements of two variables
      • - Correlation coefficient (Human Biology only)
      • Investigations involving finding the number of individuals in particular categories
      • - Chi-squared test
    • 96.
      • Standard deviation is not a statistical test
      • Some weakness with null hypothesis
      • Variation with choice of test
      • - suggests lack of experience with tests
      • Explanation of choice weak
      • - suggests insufficient familiarity with Student Statistics Sheet
      • Calculations good overall
      • Explanations generally lacked reference to both probability and chance
    • 97.
      • Investigate populations
      • - study a habitat
      • - use frame quadrats and line transects
      • - measure an abiotic factor
      • - measure abundance (population density) by percentage cover and frequency
      • Photosynthesis
      • - effect of limiting factor (light intensity / CO 2 concentration / temperature) on rate
      • Respiration
      • - effect of substrate / temperature on rate in an organism
      • Taxes and Kineses
      • - the effect of external stimuli
    • 98.
      • Growth
      • - measurements of patterns of growth
      • Meiosis
      • - observations of stages (to compare with mitosis)
      • Mendelian inheritance
      • Perception of stimuli
      • Biodiversity
      • - measure an abiotic factor
      • - measure frequency, population density and percentage cover
      • Factors affecting the rate of photosynthesis
      • Factors affecting the rate of respiration
      • The effect of antibacterial agents on the growth of bacterial culture
    • 99.
      • Skill
      • Random sampling
      • Use of 3-way tap
      • Establishing anaerobic conditions
      • Opportunity
      • - Measure abundance
      • - Respiration in yeast
      • - Respiration in yeast
    • 100.
      • Transfer of practical and investigative skills from AS during Tasks
      • Equipment use e.g. knowledge of apparatus
      • Methodology e.g. use of a control
      • Terminology e.g. reliable, valid etc.
      • Table skills still required
      • Identifying type of graph to use still possible
      • Calculations still expected (of rate, mean, standard deviation and percentage change)
      • Biological ideas brought forward e.g. enzyme action.
    • 101.
      • Reading the question stem
      • - it provides the focus or context for the answer
      • Answering the question asked
      • Using language that is helpful
      • - “It will change / effect / alter …..” But how? What is ‘it’?
      • Recognising the number of marks available
      • Defining ‘Control’
      • - What is a suitable control? The same volume is needed so something must be replaced
      • - Why is a control used? To show the independent variable is responsible for any change
      • Describing what standard deviation bars show and explaining their use
      • - if they do not overlap differences are real
      • - the longer the bar the greater the variation in or spread of data
    • 102.
      • For testing
      • - mathematical skills
      • - understanding of HSW terminology
      • - understanding of terms used in exams
      • - knowledge of practical techniques
      • - appreciation of investigative skills
    • 103.  
    • 104.
      • A student made up a 1% solution of amylase using water and a 10% solution of amylase. Draw a table to show the volume of water and the volume of 10% solution of amylase that a student would need to make 10 cm 3 of a 1% solution of amylase.
      • Draw a table to show how you produced the 5 different concentrations of reducing sugar solution.
    • 105.
      • How many repeats of each pH did you take? Use you data to explain how you decided on the number of repeats to take.
      • Explain why you set up three experiments at each temperature.
      • How many readings did you take for each of the sucrose solutions? Use your data to explain why you took this number of readings.
      • Was the number of repeats you carried out for each length of time you spent exercising enough to give reliable results? Use your results to justify your answer.
      • Increasing the number of repeats in an investigation increases the reliability of the results. Explain how.
    • 106.
      • You incubated one of your starch solutions with 2% amylase solution and the other starch solution with 1% amylase solution. There is more reducing sugar in the mixture incubated with 2% amylase than the mixture incubated with 1% amylase. Suggest how you could use Benedict’s solution to compare the amount of reducing sugar in the two mixtures.
      • Describe a method to compare the amount of reducing sugar that might be found in the liquid surrounding a visking tubing bag.
    • 107.
      • You are provided with a 1cm 3 sample of a bacterium in a liquid culture medium and an outline method for estimating the number of live bacteria in a culture.
      • • Produce known dilutions of the culture
      • • Use aseptic techniques
      • • Pour nutrient agar into Petri dishes
      • • Spread the culture across the agar
      • • Count the number of colonies
      • Use the outline method to describe how you could estimate the size of the bacterial population in the sample.
    • 108.
      • A doctor wanted to test a group of patients with a new drug. The patients were divided randomly into two groups. Explain why they were divided randomly.
      • Suggest how scientists divided the patients in their investigation into two equal groups.
      • During an investigation of childhood diseases, doctors divided children randomly into two groups. Explain why they were divided randomly.
      • The volunteers were divided randomly into two groups. Explain why they were divided randomly.
      • Is it important to have the same number of people in each group in this trial? Explain your answer.
    • 109.
      • The total amount of faeces that each person produced was recorded per kilogram of body mass. Explain the advantage of this.
      • The rate of energy expenditure is measured per kilogram of body mass. Explain why.
      • Each tube had a set volume of enzyme solution added. The table shows enzyme concentration in arbitrary units. Suggest appropriate units that could be used for enzyme concentration.
      • Why is the fluid intake of the athletes in this study expressed as cm 3 kg -1 body weight?
      • The Body Mass Index (BMI) is a measure of body fat. It is calculated by dividing the weight of a person by their height squared. The units for BMI are given as kg m -2 . Explain why.
      • The crop yield was measured as dry mass / tonnes per hectare per year. Explain why the yields were measured in this way.
    • 110.
      • A student wanted to improve her investigation of the effect of temperature on milk digestion by trypsin, by using control experiments. She set up a test tube containing milk and buffer at each temperature. She did not add trypsin to these tubes. What would these control experiments show?
      • Doctors investigated the effect of drinking caffeinated tea on heart rate. What treatment should those in the control group receive? Explain your answer.
      • It is not essential to have the same number of people in the experimental and control groups in an investigation like this. Explain why it is not essential.
    • 111.
      • Doctors investigated the effect of different types of ORS in the treatment of patients suffering from a severe intestinal infection. They treated the control group with standard ORS. Explain why a control consisting of no treatment was not used.
      • During an investigation into the effect of amylase concentration on the digestion of starch, one student suggested the investigation could be improved by carrying out an experiment with starch but no amylase. Do you agree that this would improve the investigation? Explain your answer.
      • Appropriate control experiments should be carried out when necessary. Explain why.
    • 112.
      • Explain the difference between monitoring a variable and controlling a variable.
      • Use information from your investigation to explain what is meant by (a) controlling a variable, and
      • (b) monitoring a variable.
      • Describe how monitoring a variable differs from controlling a variable.
      • Describe and explain what you did to make sure the temperatures of the water baths were as reliable as possible.
      • Describe how you monitored the temperature of the water bath.
      • You were told to use a water bath at 35 o C. How can this temperature be monitored?
    • 113.
      • Evaluate the usefulness of the range and standard deviation in comparing data about pulse rates from the athletes and non-athletes.
      • Calculate the percentage increase in the mean number of red blood cells in the athletes’ blood after training at high altitude. Show your working.
      • A teacher collected class data for the time it took for all the starch to be digested at 60 °C. He then calculated the mean and standard deviation for the data. What information does the standard deviation provide?
      • Drug A reduces the mean concentration of amylase in the blood. Calculate the percentage reduction in amylase concentration when people with pancreatitis take this drug. Show your working.
      • Describe and explain the relationship between standard deviation and the reliability of the results.
    • 114.
      • Use your data to calculate the mean (time) and standard deviation.
      • Percentage change in diameter of the plant material is better to use than change in diameter. Explain why.
      • Calculate the percentage reduction in use of glycogen in the trial compared with water.
      • Variation in a data set can be measured using standard deviation, or shown by the range of the data. Standard deviation is a more useful measure of variation. Explain why.
      • The BMI for non-overweight children is given as 15.7 ± 0.5. Explain what information this provides.
      • It is better to use percentage change in mass of potato cylinders than change in mass. Explain why.
      • Which treatment shows the greater effect on the number of bacteria. Use a calculation to support your answer.
    • 115.
      • You put a tube containing the enzyme and a tube containing the substrate in the water bath before you mixed them. The tubes were left in the water bath for five minutes before they were mixed. Explain why this was necessary.
      • Five minutes may not have been long enough. Suggest how you could find out when they should be mixed.
      • You left the test tubes in the water bath for 10 minutes before you added the enzyme to the substrate. Explain why.
      • You put the tubes containing the separate amylase and starch solutions in a water bath for 10 minutes before mixing. Explain why.
      • You left Tube 1 and Tube A in the water bath before mixing their contents. Explain why.
    • 116.
      • In each experiment, how did you determine when all the starch had been digested and no further samples needed to be taken?
      • How did you decide that the end point had been reached in all of your tubes?
      • Explain why your method may not have given an accurate measure of the time taken for colour change to be complete.
    • 117.
      • A student produced a bar chart to show the results of his experiment with amylase. Why was this type of graph unsuitable?
      • The investigation examined whether there was a correlation between two variables. In this investigation, what was the dependent variable? Explain your answer.
      • The 5 different types of milk turned various shades of pink when the reagent was added. What type of graph would you use to plot these results. Explain your answer.
    • 118.
      • The results you collected should be accurate. Explain what is meant by accurate results.
      • The conclusions you came to using your graph may be more reliable that those from the graph of another student. Suggest why.
      • Is the conclusion of the study valid? Explain your answer.
      • A positive result from a test for reducing sugar indicates that glucose is present. Is this statement reliable? Explain your answer.
    • 119.
      • A student was asked to combine data from several people in her group. She did not think the combined data would be reliable. Give 2 reasons why the combined data would not be reliable
      • Use your results to explain whether or not the data you collected are reliable or not.
      • You measured the foot length and foot width of five people. Use your data to explain whether foot length or foot width is the more reliable measure of foot size.
    • 120.
      • Use your raw data to identify whether the results you obtained were reliable or not. Explain your answer.
      • Reliable data are obtained if the sample used in an investigation is random.
      • Give two reasons why you believe your data is reliable.
    • 121.
      • Temperature affects the rate at which pieces of cut apple go brown. Describe how you would take into account the effect of temperature when investigating the rate at which pieces of cut apple go brown.
      • Temperature can be an experiment variable. Was this variable controlled during your investigation? Explain your answer.
      • Investigations that involve growth of bacteria should include the control of temperature. Explain why. You were asked to carry out your investigation at room temperature. Did you use a water bath at room temperature? Give the reason for your answer.
      • You were told to use a water bath at 60 °C. Explain why a water bath is used.
      • Did you use a water bath at room temperature? Explain the reason for your choice.
      • Describe how you would maintain a water bath at 10 o C.
    • 122.
      • During your investigation into the effect of amylase on starch you used a pH7 buffer solution.
      • (a) Explain why you should add buffer solution to the amylase.
      • (b) Suggest why a pH7 buffer solution was used.
      • You used a buffer solution in your investigation. What are buffer solutions used for?
      • Buffers are often used in enzyme-controlled experiments. Explain why.
      • You used a buffer solution in your investigation. What are buffer solutions for?
    • 123.
      • Describe how you kept one named variable constant in your investigation
      • Rate of reaction was the dependent variable in the investigation. Explain why it is described as the dependent variable.
      • Other than temperature and size of pieces of cut apple, give one other variable you would keep constant.
      • What was the independent variable in your investigation? Explain your answer.
      • What was the dependent variable in your investigation? Explain your answer.
      • You should keep the lamp the same distance from the plant throughout the investigation. Explain why.
    • 124.
      • Explain how the statistical value can be used to interpret the data you collected.
      • A student performed a statistical test on the results he obtained at 32 o C and 51 o C. He obtained a value of p = 0.0292. How should he interpret this value. Explain your answer.’
      • Describe a statistical test scientists could use to see if there is any relationship between the yields of biofuel crops and the amount of fertiliser used to grow these crops.