Osmosis in Plant Tissues-Moderator Comments
Criterion
Achievement level awarded
Achievement of aspects
D
DCP
CE
5
4
c, p, c
p, c, p
Assessment
Design
Not assessed. The teacher decided not to assess this criterion having given the students a lot of guidance on the
method to be used.
Data collection and processing
Recording raw data
Complete
The correct data is recorded.
Processing raw data
Partial
Raw data has been appropriately processed. The isotonic molarity can be calculated from the intercept of the trend
lines with the x-axis and then converted to solute potential using the graph provided. However, as the computerdrawn graph has no graduations included on the axes or gridlines to determine the intercept points accurately, only a
partial can be awarded.
Presenting processed data
Complete
Good use of trend lines to reveal the uncertainties in the data and some conventions for graph drawing are
respected.
Conclusion and evaluation
Concluding
Partial
The conclusion is partially correct. The water potential of the plant tissues may be due to the presence of sucrose but
there are other solutes that will be present in the cell sap.
Evaluating procedure(s)
Complete
Errors due to the precision of the balance are discussed. As the degree of precision of the balance is ± 0.1 g (given in
the data) this is a valid criticism as the change in mass is 0.6 g at the most. Drying off the residual solution at the end
is also a valid source of error. This aspect achieves complete.
Improving the investigation
Partial
Not drying off the tissue cores after soaking would be a bad idea, it would probably lead to a large source error.
Cutting and weighing extra tissue samples would not have taken a lot of extra time. This aspect only achieves partial.
Behaviour in Invertebrates-Moderator Comments
Criterion
D
DCP
CE
Achievement level awarded
5
6
3
Achievement of aspects
c, p, c c, c, c p, p, p
Assessment
Design
Defining the problem and selecting variables
Complete
The student has identified and stated a clear and focused research question. It would have been preferable if the
sources of information stated in the background had been given. Only three temperatures are selected. The
dependent and independent variables are correctly identified. There is a good attempt to state and explain the
variables that should be controlled.
Controlling variables
Partial
The method effectively explains how the independent variable, temperature, would be altered and the temperatures
to be investigated and the methods used to set the temperatures accurately are clearly stated. However, the method
would not allow for the control of temperature to be precise enough. The variables that should be controlled are listed
and the methods for their control are described but there are some omissions.
Developing a method for the collection of data
Complete
The method for recording the movement of the maggots is clearly stated. Ten replicates are proposed for each
temperature. This is a sufficient number of repeats at this level although only three temperatures are to be
investigated, with the temperatures used not being evenly spaced. This would produce sufficient data to be effectively
analysed, conclusions to be drawn and the investigation to be fully evaluated.
Data collection and processing
Recording raw data
Complete
The table of results is neatly drawn with the columns and rows clearly headed. The units used are stated clearly.
There are statements of uncertainties and the limits of accuracy of the apparatus used in the measurement of
temperature or time.
Processing raw data
Complete
The data is processed properly with the calculation of averages, standard deviations and rates of movement, and the
processed results are presented in the form of a bar chart. The calculation of the means produces figures stated to
one decimal place and the calculation of the rates of movement produces figures stated to three or four decimal
places, where the original data is in whole numbers only. Students should be encouraged to be consistent in their use
of significant figures when presenting quantitative data. Standard deviations are calculated but there is no attempt to
make any statistical comparisons between the results at the different temperatures. However, there has been
sufficient processing of the data to warrant the award of complete.
Presenting processed data
Complete
The bar chart aids interpretation of the data as the axes are labelled clearly and the temperatures are stated
quantitatively as well as qualitatively. Errors and uncertainties are stated, and bars representing the standard
deviation values are included in the chart. This processing is complete enough for this level.
Conclusion and evaluation
Concluding
Partial
Only a simple conclusion is written, that is, that the maggots moved faster at a higher temperature than at a lower
temperature. The investigation has not provided enough data, with only three temperatures for a firm conclusion to be
drawn. The statement that the rate of movement is in direct proportion to the temperature is incorrect. There is no
proper justification for the statements made and no reference to theory or literature.
Evaluating procedure(s)
Partial
There is a reasonable evaluation of the weaknesses and limitations of the investigation. There is the observation that
the trend shown is not a straight line. This contradicts the statement made in the conclusion. There is some
appreciation of the flaws in the investigation but the most obvious problem of the selection of only three unevenly
spread temperatures is not fully discussed and that all of the maggots used should have been from the same batch
and of the same age, as maggots of different ages may show different responses.
Improving the investigation
Partial
There are some relevant suggestions for improving the investigation but overall these are simplistic. The fact that the
temperature of the room used for the investigation would be likely to fluctuate is mentioned. However, no suggestions
about how to overcome this are given.
Investigating Yeast Peroxidase-Moderator Comments
Criterion
D
DCP
CE
Achievement level awarded
4
6
5
Achievement of aspects
c, p, p c, c, c p, c, c
Assessment
Design
Defining the problem and selecting variables
Complete
The aim is focused, the organism used is correctly identified and a small amount of background information helps to
put the investigation in context. Reference sources are clearly indicated in footnotes. A hypothesis is presented,
though this is not a necessity for the assessment of design, it does help to identify the independent and dependent
variables. These variables, however, need to be specifically identified to achieve complete for aspect 1.
The independent and the dependent variables are finally identified. Several important variables that need controlling
are also listed.
Controlling variables
Partial
Some monitoring of the environmental temperature is stated but the student does not attempt to control it when it
would have been easy enough to use a beaker of water. The concentration of the yeast suspension will vary as the
yeast cells sediment out of the liquid. If the suspension is not stirred before sampling this could affect the results.
Developing a method for the collection of data
Partial
The concentrations of the solutions are stated. The composition of the buffer (phosphate, citrate, and so on) could
also have been indicated but it may have been provided as an off-the-shelf reagent and information on its
composition may not have been provided. The student could, however, have inquired about its composition.
Though the data collection is automated using a data logger, the student is responsible for the settings in the data
collection. This is sufficient for aspect 3 of design. However, only one replicate is performed for each of the
concentrations of H2O2. As the data collection is automated and the results are rapidly obtained it is not unreasonable
to expect replicates. Therefore, insufficient data is collected. Aspect 3 of design is only partially attained.
Data collection and processing
Recording raw data
Complete
The temperature curves are raw data. These count towards data collection and presentation (DCP) aspect 1. This is
a clearer presentation of the data than printing out numerical values. Uncertainties are given for the temperature
probe. They are presented with an unambiguous title and a key is provided.
Processing raw data
Complete
The table of initial reaction rates is calculated from the raw data using the linear plot facility of the program. This
facility has to be selected from the range of curve fitting options and the student had to decide upon the period when
the reaction rates are to be determined. On its own this is insufficient to achieve complete for aspects 2 and 3. The
resulting curve would be required.
Presenting processed data
Complete
The best-fit line in the graph meets the requirement for aspect 3. The subject guide states “the treatment of
uncertainties in graphical analysis requires the construction of an appropriate best-fit line”. The best-fit line combined
with the R² value for the curve is sufficient to award a complete for aspects 2 and 3.
Conclusion and evaluation
Concluding
Partial
Aspect 1 of conclusion and evaluation (CE) is only partially met. Although one cannot predict the maximum velocity of
the peroxidase enzyme in a given sample of yeast cells (there are too many unknown factors that could affect this), it
would be expected that the curve would be compared with others obtained for peroxidases or other enzymes. Thus,
there is no research of literature values.
Evaluating procedure(s)
Complete
The main weaknesses of the investigation, as revealed by the data that is collected, are identified.
Improving the investigation
Complete
Realistic improvements are proposed for these weaknesses.