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Reflections on Practical Assessment
and Improving Student Outcomes
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
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
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
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
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
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
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)
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)
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
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)
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?
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
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
A*A* AA BB CC DD EE UU
A level A level HumanHuman
20092009 13.113.1 34.434.4 57.057.0 77.377.3 92.992.9 100100
20102010 3.03.0 11.811.8 31.231.2 54.654.6 77.577.5 93.493.4 100100
A level A level BiologyBiology
20102010 8.88.8 29.429.4 52.552.5 72.172.1 88.288.2 97.297.2 100100
National A National A levellevel
20102010 8.08.0 28.528.5 51.751.7 72.472.4 87.687.6 96.896.8 100100
AS HumanAS Human 20092009 7.57.5 18.318.3 35.635.6 53.953.9 69.169.1 100100
20102010 8.88.8 21.021.0 40.740.7 57.057.0 73.173.1 100100
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
UnitUnit Unit totalUnit total A*A* AA BB CC DD EE
11 8080 4949 4444 3939 3434 3030
22 8080 5858 5252 4646 4141 3636
3T3T 5050 4040 3737 3434 3232 3030
3X3X 5050 3333 3030 2727 2424 2222
44 9090 6767 6262 5757 5252 4747 4343
55 9090 7070 6565 6060 5555 5050 4646
6T6T 5050 4242 3939 3636 3333 3030 2727
6X6X 5050 3737 3434 3131 2929 2727 2525
Molecule Ion Compound Element Isomer Isotope
Bond Oxidation Reduction Hydrolysis Condensation Wavelength
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
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?
….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.
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
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
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
Use of an optical microscope- preparing temporary mounts - staining- estimation of size
Exercise- changes in heart rate - changes in ventilation
Mitosis- observation of stages
and how could they be incorporated?
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
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
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…….”
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 xn
,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
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
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 720to complete a stage total number of cells counted
StageStage Number of Number of cellscells
Time in each Time in each stagestage
InterphaseInterphase 177177 504504
ProphaseProphase 44 7.27.2
MetaphaseMetaphase 77 14.414.4
AnaphaseAnaphase 11 28802880
TelophaseTelophase 6363 180180
Stage of Stage of mitosismitosis
Number of cells Number of cells in stage of in stage of
mitosismitosis
Percentage of Percentage of cells in stage of cells in stage of
mitosismitosis
Time to complete Time to complete stage of mitosis / stage of mitosis /
minutesminutes
ProphaseProphase 108108 0.740.74 72.972.9
MetaphaseMetaphase 1616 55 21.621.6
AnaphaseAnaphase 88 1010 13.513.5
TelophaseTelophase 2828 2.862.86 3.853.85
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 Stage of mitosismitosis
Number of Number of cells in cells in stage of stage of mitosismitosis
Percentage of Percentage of cells in stage cells in stage
of mitosisof mitosis
Time to complete Time to complete stage of mitosis / stage of mitosis /
minutesminutes
ProphaseProphase 108108 112.5112.5 5454
MetaphasMetaphasee
1616 1010 88
AnaphaseAnaphase 88 55 44
TelophaseTelophase 2828 17.517.5 1414
Know the Institute of Biology conventions- n.b. 3rd 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
Investigation example
produces data of time taken for pH indicator to turn blue following exposure of respiring bacteria to different temperatures
- worksheet
Table 1
Temperature (oC)
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
Table 2
‘Effect of temperature on time taken to change colour’
Time (s) Average(s)
Temp oC 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
Table 3
Test tube Temperature of water bath
Time taken to turn blue
Repeat time taken to turn blue
Average
1 20 oC 7 minutes 15 seconds
7 minutes 11 seconds
7 minutes 13 seconds
2 30 oC 2 minutes 1 minute 45 seconds
1 minute 52.5 seconds
3 40 oC 36 seconds 47 seconds 41.5 seconds
4 50 oC 34 seconds 31 seconds 32.5 seconds
5 60 oC 8 minutes 57 seconds
9 minutes 33 seconds
9 minutes 15 seconds
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
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
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
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)
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
- worksheets
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
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.”
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?
Question - ‘Describe how you would maintain a water bath at 10oC’
What is being asked?- why use a water bath? or- how to monitor the temperature? or- how to keep the water at 10oC?
Suggestion - use similar examples for group work
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.”
“Which stage of mitosis; prophase, metaphase, anaphase or telophase, did
you find takes the longest time to complete?”
Answer: ‘Interphase’
“Explain the change in the mean number of metaphases over the first six hours”
Answer: “……..After six hours the cells……”
“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 6th hour. From 0 to 6 hours the mean number has increased by 30, that means it has doubled during the 6 hours.”
Glossary for Instructions in question papers- Describe- Explain- Suggest- Evaluate- Give- Name
Glossary for How Science Works
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
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)
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
- worksheet
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
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
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.
“Urease catalyses the reaction
urea + water ammonia + carbon dioxide.
What name is given to the type of reaction that urease catalyses?”
Answer ?????
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
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
Task 1 (8)Task 1 (8) Task 2 (12)Task 2 (12) Sect A (14)Sect A (14) Sect B (16)Sect B (16)
Example 1Example 1 22 66 55 22
44 1212 1010 99
22 88 88 66
22 99 66 99
22 88 55 66
33 1212 77 88
22 55 66 22
Example 2Example 2 44 99 33 22
11 1111 88 55
44 1212 1111 1010
44 1212 66 77
11 1111 22 33
44 1111 44 33
33 1212 88 44
Task 1 (10)Task 1 (10) Task 2 (10)Task 2 (10) Sect A (15)Sect A (15) Sect B (15)Sect B (15)
Example 1Example 1 66 99 99 66
66 77 77 55
33 99 55 22
22 77 66 55
33 88 55 44
44 99 88 88
44 1010 99 66
Example 2Example 2 44 44 77 88
44 66 44 44
55 99 88 44
44 66 1111 77
22 66 66 22
33 88 44 11
22 44 55 11
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
Using one task to develop and test many ideas- As a class exercise or homework- From a practical investigation
Examples….
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 / dm3 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
Practical - A dilution series use pipettes and e.g. a 100% glucose
solution to make 10cm3 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???
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
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
A researcher investigated whether the weight of a person was related totheir height. He measured the weight and height of ten people. His resultsare shown in the table.
(a) 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.
Extension1 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
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
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
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
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
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
‘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.’)
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 levelcritical valueaccept or reject null hypothesischance
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
89
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
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. OrSoil moisture content has no effect on the number of dandelions in a field.
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 – Interpreting the statistical test – an example (1an example (1))
• 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
• 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
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
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
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 / CO2 concentration / temperature) on rate
Respiration- effect of substrate / temperature on rate in an organism
Taxes and Kineses- the effect of external stimuli
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
Skill
Random sampling Use of 3-way tap Establishing
anaerobic conditions
Opportunity
- Measure abundance
- Respiration in yeast
- Respiration in yeast
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.
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
For testing - mathematical skills- understanding of HSW terminology- understanding of terms used in exams- knowledge of practical techniques- appreciation of investigative skills
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 cm3 of a 1% solution of amylase.
Draw a table to show how you produced the 5 different concentrations of reducing sugar solution.
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.
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.
You are provided with a 1cm3 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.
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.
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 cm3 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.
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.
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.
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 35oC. How can this temperature be monitored?
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.
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.
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.
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.
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.
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.
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.
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.
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 10oC.
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?
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.
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 32oC and 51oC. 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.