22.2 - Recording Results in a Table

What a table question looks like

• Nearly every Cambridge practical paper asks you to make a table:
  • Paper 5 - Record readings as you take them
  • Paper 6 - Fill in results you're given
• The examiner marks the structure of the table, not the biology - and the marks are always the same.

A typical question

A student is going to measure the time taken for starch to disappear when amylase is added, at five different temperatures. Each temperature is tested three times.

Draw a table the student could use to record the results. [3]

The three fixed marks

1. Draw it as one table with enough columns and rows, and a ruled line under the headings (1 mark).
2. Head each column with the quantity and its unit, written as "quantity / unit" (1 mark).
3. Record every reading in the right place, to a consistent precision (1 mark).

Completing a table:

• When the paper gives you the readings already and asks you to complete or process a table, the same three things are marked, plus any calculation such as a mean.
• A results table is one of the most dependable marks on the paper, because the rules never change from one experiment to the next.

Setting out a results table

• A results table gives every number you collect a place, laid out so the pattern can be read down the columns.
• Draw it before you start the experiment, so you're not designing it while readings are coming in.
• Draw the whole thing with a ruler, including a ruled line under the row of headings.
  • The mark scheme specifically looks for that header line.
  • A heading that "floats" above the columns with no line under it can lose the structure mark.

Which columns to include

• First column - The independent variable (the thing you change), with its values going down in order.
• Middle columns - The dependent variable (the thing you measure), with one column for each repeat.
• Final column - The mean.

For example, testing five temperatures three times each needs a first column for temperature plus four more: one for each of the three repeats, and one for the mean.

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Worked example - Amylase results table

A table that scores for an amylase experiment testing five temperatures, three repeats each:

• The temperatures go down the first column in even steps.
• Each repeat has its own column.
• There's a column ready for the mean, so everything the experiment produces has somewhere to go.

Headings and units in a results table

• Write each column heading as the quantity followed by its unit, separated by a slash: "Temperature / °C", "Time / s", "Length / mm".
• The slash reads as "temperature divided by the unit", so the values underneath are written as plain numbers with no unit next to them.
• Putting the unit in the heading once - not after every value - is what the mark scheme rewards.
• The heading carries a mark of its own, and leaving the unit off is one of the most common ways to lose it.

Choosing the right unit

• Wrong unit for the instrument - Match the unit to the instrument. A stopwatch reads in seconds, so the heading is "/ s", not "/ min".
• Using "m" for minutes - "m" reads as metres, so don't use it for minutes.

Filling in readings into a results table

• Record the actual measured value, not a label. If one tube was in hot water and one in cold, record the temperatures you measured (e.g. 45 °C and 12 °C), not the words "hot" and "cold".
• Every cell holds a number - the table is a record of measurements.

Keep the precision consistent

• Keep the same precision all the way down a column. If your stopwatch reads to the nearest second, every time in that column ends in a whole number of seconds - you don't write 42 in one row and 42.5 in the next.
• Match the precision to what the instrument can show. A thermometer marked every degree is read to the nearest degree, not to a tenth.

Working out the mean

• Where the table has repeats, the last column is the mean.
• Add the repeats for that row and divide by how many there are.
• Round the mean to the same precision as the readings it came from.
• If a repeat is clearly anomalous - an odd one out well away from the others - leave it out of the mean and note it.

Common exam questions

Question 1

How should the heading of a column that records temperature in degrees Celsius be written?

As "Temperature / °C" - the quantity, then a slash, then the unit - so that the values below can be written as plain numbers.

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Question 2

A student writes "20 °C, 30 °C, 40 °C" down the temperature column of a table. Why might this lose a mark?

Because the unit should appear once, in the heading, not beside every value; repeating the unit in the body counts as the unit not being in the heading.

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Question 3

An experiment measures the time for a colour to change at five temperatures, with three repeats at each. How many columns should the table have, and what is the last one for?

Five columns: one for the temperature, three for the three repeats, and a final column for the mean time.

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Question 4

A student draws a separate table for each temperature tested. What is wrong with this?

Cambridge wants a single table with one row per temperature, so the results can be compared down the columns; separate tables do not score the structure mark.

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Question 5

One of the three repeats for a temperature is much higher than the other two. What should you do with it when finding the mean?

Treat it as an anomaly, leave it out of the mean, and find the mean from the two consistent repeats.