Revise Recording Data: Tables, Units & Repeats for Biology 3 (IAL) WBI13 (AS Level) — revision notes and instant AI marking. Free to start.
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Edexcel IAL Biology • Unit 3: Practical Skills in Biology I
Recording Data: Tables, Units & Repeats
📋 Big idea: A results table is marked before anything is plotted. Headings with units, a consistent number of decimal places, the independent variable on the left and the mean worked out to the right — these are marks awarded for the table itself, independent of whether the experiment worked.
Summary — What This Topic Covers
Laying out a results table that gains the presentation marks
Writing headings with units in the correct form
Why every value in a column needs the same number of decimal places
How many repeats, and what a mean does and does not fix
Independent variable in the leftmost column, in ascending order
Dependent variable repeats to the right, then the mean
Units in the heading only — never repeated beside every number
Every value in a column to the same number of decimal places
Ruled lines, and no empty cells
2. Headings and Units
The convention
Write the quantity, then a solidus, then the unit: Temperature / °C, Volume of oxygen / cm³, Rate / cm³ s⁻¹. The column then contains bare numbers.
✓ Time / s 45 60 75
✗ Time 45 s 60 s 75 s
✗ Time (seconds) 45 60 75 ← acceptable, but / is preferred
✓ Rate / cm³ s⁻¹ 0.24 0.31 0.42
✗ Rate / cm³/s ← use negative indices, not a second solidus
Common mistake
Two solidi in one unit. "cm³/s" reads as ambiguous; write cm³ s⁻¹. With one solidus already separating quantity from unit, a second one is genuinely confusing.
3. Decimal Places
The rule
Every value in a column must be recorded to the same number of decimal places, set by the resolution of the instrument — not by what the number happened to look like.
✗ 4 ✓ 4.0
4.5 4.5
4.25 4.0 ← a 0.5 cm³ syringe cannot give 4.25
A mean may be given to ONE extra decimal place, because averaging
several readings justifies slightly more precision:
4.0, 4.5, 4.0 → mean 4.17 cm³
What mark schemes look for
A column reading 4, 4.5, 4.25 tells the examiner you recorded whatever the calculator gave rather than what the apparatus could measure. It costs the table mark.
4. Repeats and Means
Key Term
Repeats are measurements of the same condition, taken under identical settings. Their mean is more reliable than any single value because random errors partly cancel.
Three repeats is the normal minimum at this level; more is better
A mean of three lets you spot an anomaly — with two you cannot tell which is the odd one
Exclude anomalies before calculating the mean, and say that you did
The range or spread of repeats tells the reader how much you should trust the mean
What a mean cannot do
A mean reduces random error only. If the balance has a zero error, every repeat is wrong by the same amount and the mean is wrong by exactly that amount too.
5. Raw Data vs Processed Data
Keep the two separate and visible. Raw data is what you read off the instrument; processed data is anything you calculated from it.
RAW PROCESSED
────────────────────────────────────────────────────────────
initial and final mass / g % change in mass
volume of gas / cm³ rate / cm³ min⁻¹
time taken / s 1 ÷ time / s⁻¹
number of bubbles bubbles per minute
Easy marks
Show the calculation once, in full, beneath or beside the table. A processed column with no visible working is a column an examiner cannot award method marks for.
Practice Questions
Practice Question 1
A student's table is headed "Volume" and each cell reads "12 cm³", "14 cm³", "15 cm³". Give two improvements.
Practice Question 2
Explain why three repeats are recommended rather than two.
Practice Question 3
A student calculates a mean of 4.166666 cm³ from readings of 4.0, 4.5 and 4.0. State what they should write, and why.
Practice Question 4
A student takes five repeats and calculates a mean, but their results are still inaccurate. Explain how this is possible.
What to Memorise
IV on the left, ascendingUnits in the heading onlyQuantity / unit, e.g. Time / scm³ s⁻¹ not cm³/sSame decimal places down a columnMean may take one extra d.p.Three repeats minimumExclude anomalies before the meanMean fixes random, not systematic
Concepts Checklist
Exam Tips
What mark schemes look for
The table is marked on its own: headings with units, consistent decimal places, IV on the left, no units in the cells. These marks are available before the experiment even works.
The trap
Recording whatever the calculator displays. A 0.5 cm³ syringe cannot produce 4.25 cm³, and writing it says you were not thinking about resolution.
Easy marks
Show one worked calculation beside a processed column. It takes a line and it is often worth a mark in its own right.
Worth remembering
If a question says the repeats agreed closely but the answer was still wrong, it is pointing at systematic error — and no number of repeats will help.