Collecting, Recording & Processing Data
Navigate the knowledge tree: 🌿 Biology ➡ NCEA Level 2 Biology ➡ 2.1 Investigation ➡ Lesson 7: Collecting, Recording & Processing Data
Measure and record data carefully and accurately.
Organise my data in clear results tables.
Check the data for mistakes or unusual results.
Calculate mean percentage change in mass.
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Accurate data collection is essential because any mistakes made here cannot be fixed later. If measurements are wrong, your calculations, graphs, and conclusions will also be wrong.
To measure and record accurately, make sure to:
Zero the balance before use
Meausre the mass in grams (g)
Record to the same number of decimal places
Blot kumara pieces consistently
Record data immediately (not from memory)!!!
Measuring and recording your data accurately helps to improve the validity of your investigation because your recorded data is more likely to measure what they are meant to. It also helps improve the reliability of your results because your repeat measurements are more likely to be consistent.
You measure a kumara piece and record its mass as 6.2 g. Your partner records the same piece as 6.237 g. Which measurement is better, and why?
Answer: The measurement 6.237 g is better.
It is more precise because it records more decimal places. As long as the balance allows this precision, it improves accuracy and consistency across data.
A good quality and well-organised results table must have:
A clear title
Column headings
Units in brackets in the column heading
Consistent decimal places for each quantity
Raw data recorded first
When well-organised, data tables prevent confusion, make errors easier to spot, and make data processing a lot more straightforward.
As you record the data, check each value and see if you can recognise any emerging patterns. You must also check for:
Missing values
Values that don't seem to match the emerging pattner
Large differences between repeats.Â
These unusual results are called anomalies, and they can skew averages, mislead conclusions and make your results less reliable. They should be identified, but not necessarily removed.Â
Three % change values for 0.6 M sugar are:
−8.2%
−8.6%
+2.1%
Is one value unusual? What should you do?
Answer: Yes, +2.1% is unusual. It should be checked for error but not removed without a reason.
The other results show mass loss, which matches osmosis theory. A mass gain is unexpected and may be due to error (e.g. poor blotting).
We cannot analyse trends in mass change because the conlusions would be misleading. If we only looked at 'mass change' we would not be acknowledging the fact that:
The kumara pieces started at slightly masses (initial mass)
A 0.5 g change is more significant for a small piece than a large one
So instead, we use percentage (%) change in mass because it accounts for the starting size of each piece and allows for a fair comparison.
A kumara piece had an initial mass of 5.00 g and a final mass of 4.50 g. Calculate % change in mass.
Answer: -10%
change in mass = (4.50 - 5.00) / 5.00 = -0.10 g
% change in mass = -0.10 x 100 = -10%
The negative value shows mass loss. Using percentage change allows comparison with other pieces.
It's important to calculate the mean because repeats are never identical due to random error. (Remember that random errors are caused by things like slight differences between samples, small environmental changes and natural biological variation).Â
To reduce the effect of random error, its crucial to repeat measurements and calculate means. The mean:
Smooths out variation
Gives a more reliable value
Represents the overall trend
Three % change values at 0.8 M: −12.0%, −11.5% and −12.3%. Calculate the mean.
Answer: -11.9 %
mean % change in mass = -(12.0 + 11.5 + 12.3) / 3 = -11.9%
Averaging reduces the effect of small random differences between repeats.
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