IB Biology

Internal Assessment

Processing Data

(aspects 2 & 3 of DCP)

Processing raw data & presenting processed data

To help show the trends in data Biologists usually have to use statistics & draw graphs.

This is because of the variability of the material used as well as variation due to its manipulation.

A student could show this by calculating a “margin of error”. – The simplest would be plus or minus the range of

measurements or plus or minus half the range of measurements.

– If the data permits, the error margin could be represented by plus or minus the standard deviation of the mean or the standard error of the mean.

These ranges may be expressed as error bars on graphs. Though this is not obligatory

The three written parts of Processing

If you calculate something from the data (eg averages, standard deviation, rate of reaction)

1. Write a paragraph explaining why you are doing this calculation

2. Explain how you did the calculation

3. Give details of ONE example

Showing Trends (2)

• Do a scatter graph or a bar graph of your processed data

• show errors and use statistics (for e.g.):

– the range of data, or– standard deviation– R2 value– Trend line

using ‘error bars’ or trend line. NOT BOTH.

Your title should go here !

0

20

40

60

80

100

120

0 10 20 30 40 50 60 70 80

label the axis (w ith units)

labe

l the

axi

s (w

ith u

nits

)

Here the student would get “complete” for aspects 2 &

3 of DCP.The relationship between the variables is plotted as a scatter plot and a trend line has been drawn.

Excel has also been used to calculate a correlation coefficient R2, which should be used in the conclusion. (The student should use R2 to comment just that it is high or low correlation. )

For aspect 3 the correct conventions are used for the graph.

•It has a clear title and •uncertainties are shown through both the use of the trend line and the degree of precision on the x-axis.

The student will have also explained, why & how they did these things in their writing.

• The graph is used to process the data by using the intercepts of the x-axis to establish the sucrose solutions isotonic to the tissue sap. So long as this graph is accompanied by a table showing how the data was processed, aspect 2 would achieve complete.

Note in this method that the calculation of the percentage change in length is not necessary as all the pieces of tissue were cut to the same initial lengths (4.0 cm).

• The graph is drawn using the correct conventions, it has a clear title and uncertainties are given by the use of trend lines. The axes have graduations on them to improve the precision of the estimate of the isotonic solutions. Aspect 3 has achieved complete.

Beware! – you have to finish the analysis …Check the Aim of your Experiment every time.

• Most of the processing has been done (calculating the average change in lengths),

• Unfortunately the comparison of apple & potato is not complete without the estimation of the isotonic solutions (where there is no change in length).

• This can only be awarded partial for aspect 2 PROCESSING.• The Potato and the apple were not compared – which was the

aim of the experiment.

Include Errors in your processing as well as in the raw data…

• The graph is drawn using correct conventions and the title is appropriate,

• but there are no uncertainties given– as degrees of precision (+/-), – as error bars or – as a trend line.

Therefore only partial can be awarded for aspect 3 of

data collection and processing.

Conclusions

• Say what the results show, without trying to explain them

• Refer to specific data from the graph or results table give examples of readings

• Say what the text book theory is

• Compare your results to the text book – to justify your conclusion.

Limitations

• Range of data

• Number of repeats

• Choice of equipment

• Effectiveness of the method

• Accuracy of the data

Improvements

Must be • Linked to the limitations• Specific – not general points• Can describe human error which was

unavoidable.

Must not• Say that you did the experiment badly