Biology IA · B · Form and function · topic 7 of 25

Beetroot and freeze–thaw · IB Biology IA idea: guide, sample graph and step-by-step plan

classic kit, new question. nice!

Not another temperature test. Count how many times beetroot membranes can be frozen before they give up their pigment.

Difficulty●○○ Gentle
KitBasic: beetroot, colorimeter or colour scale, freezer, cuvettes
TimeAbout 10 hours
FitsSL and HL
  • ✓ you like a clear, measurable experiment
  • ✓ you want a twist on a classic
  • ✓ you have a freezer and colorimeter or can use a colour scale

The big idea

← this is your RQ hook!

Beetroot cells hold a red pigment inside vacuoles, behind membranes. When membranes are damaged, the pigment leaks out. Freezing forms ice crystals that can damage membranes, and each freeze and thaw may add more damage. You measure how much colour reaches the surrounding water after 0 to 5 cycles. Expressing leakage as a percentage of a fully boiled sample gives a ceiling and makes batches comparable. Plot leakage against the number of cycles and decide whether each cycle adds the same damage, or whether the effect slows.

Make it yours: pick one twist

Copying a classic won't show your choices. Pick one of these (or invent your own) and your IA becomes yours.

Swipe for more twists →

Compare freezing temperatures

Freeze at two or three temperatures, for example a fridge freezer and a deep freezer if available.

→ Adds a second variable, so your graph has separate lines and your analysis compares them.
Compare the length of freeze

Keep cycles fixed but change the time spent frozen.

→ Asks whether the number of cycles or the total time frozen matters more.
Compare plant tissues

Repeat with another coloured tissue such as red cabbage and compare with beetroot.

→ Asks whether the pattern is general. You need a method for the second pigment.
Add a protective solution

Soak cubes in a sugar solution before freezing and compare with water.

→ Tests the idea that solutes protect cells, adding a new independent variable.
Change the readout

Use a calibration of absorbance against pigment concentration instead of raw absorbance.

→ Gives leakage in concentration units. Needs a dilution series and a fitted line.

Your Biology IA research question: run the check

Write your own question first. Then make sure it ticks every box:

  • Names the independent variable (number of freeze-thaw cycles, with the range) and the dependent variable (leakage, measured how).
  • Says how leakage is expressed (absorbance, or percentage of a fully boiled sample).
  • Says what is held constant (cube size, volume of water, soaking time, rinsing, temperature) and how you check.
  • Says how many cubes per condition, and from how many beetroots.
  • Is narrow enough for about 10 hours, with at least 5 values and repeats.

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The set-up

One way to set it up. Draw your own version, with your real volumes and times, for the Method section.

−18 °CAcubes cut to the same size,rinsed before the first freezesame freeze and thawtime every cycleblank with clean water;same cuvette each timeone fully boiled sampleis your 100 % leakage

How your Biology IA could be laid out

The usual order for a topic like this, what each part needs to show, and roughly how much of your 3,000 words it takes. The words are all yours.

Research question and context~250
Your question; why membrane damage matters for frozen food or frost-prone plants; what you expect and why.
Background biology~450
Membrane structure, what the pigment is and where it sits; how ice may damage membranes (cite); the shape you expect for your graph.
Variablestable
Independent, dependent and controlled variables, each with how you set, measure or hold it, and why it matters.
Method~400
How cubes are cut and rinsed; the freeze and thaw routine; how water is added and read; the boiled sample; repeats; enough detail to copy.
Safety, ethics, environment~60
Specific: sharp knife, stained hands and clothes, a cold freezer, disposal of beetroot. No animals used.
Raw datatable
Absorbance for each repeat at each number of cycles, with units, instrument resolution and the boiled sample.
Processing~250
Percentage leakage, mean and SD; one worked example per calculation type.
Graphs and analysis~350
Leakage against number of cycles with SD error bars; the model you fit (a line or a curve) and why; a test for the difference between cycles.
Conclusion~450
Answer with values and uncertainty; compare with published work on freeze damage; keep your claim to 0 to 5 cycles.
Evaluation~650, the biggest part!
Weaknesses ranked by effect (cube size, variation between beetroots, cut-surface leakage, thaw time); linked improvements.
Referencesnot counted
Every source for membrane theory and method.

What your Biology IA graph could look like

Made-up data, to show you the form of a strong graph, not the answer. Yours will look different. example only

0123450102030405060708090100Number of freeze–thaw cyclesLeakage / % of fully boiled sample (error bar: SD, n = 5)levelling offsame damage each cyclemean of five cubes, with SDthe zero-cycle point is not zero:cut surfaces leak tooILLUSTRATIVE · MADE-UP DATA
  • Error bars are the SD of repeated cubes, with n stated.
  • Two models drawn so the reader can see whether the effect slows or stays steady.
  • The zero-cycle point shows baseline leakage, which is why rinsing and a percentage scale matter.
  • Axis runs from 0 to 100 because the scale is percentage of the boiled sample.
  • Another graph to consider: plot the extra leakage per cycle (the difference between neighbouring cycles) to see whether damage per cycle changes.

Which uncertainty matters most?

rank them: don't just list them

Rank by the effect on your result (one leakage reading), not on the raw measurements. A chart like this, with your numbers, shows what to fix first.

Cube size (± 1 mm on 10 mm)20%Variation between beetroots15%Water volume (± 0.5 in 10 cm³)5%Colorimeter (± 0.005 at 0.20)2.5%Soak time (± 30 s in 30 min)1.7%biggest effect: discuss this first!% uncertainty in one leakage readingILLUSTRATIVE · MADE-UP NUMBERS

Your game plan

rinse first, then freeze

Tick steps off as you go. We'll remember on this device.

0 of 10 done

  1. Read and predictFind how freezing damages membranes and what the pigment is. Write down your prediction for how leakage changes with cycles, and what shape the graph should take.
  2. Trial run (1 lesson)Cut a few cubes, rinse them, soak and read. How much colour leaks before freezing? Is the colorimeter in range? How long should they soak? Fix problems now.
  3. Decide cube size and boiled controlChoose one cube size and how you will cut it consistently. Decide how a fully boiled sample is made, and use it as 100 %.
  4. Decide cycles, repeats and timingChoose at least 5 values of cycle number, repeats at each and fixed times for freezing, thawing and soaking. Write down why for each.
  5. Collect the dataRecord absorbance for each repeat straight into the table, with the filter and blank noted. Note any cubes that crumbled or any odd colours.
  6. ProcessConvert each reading to percentage leakage. Calculate means and SD, and do one worked example.
  7. Graph and fitPlot leakage against cycles with error bars. Decide whether a straight line or a curve describes the data better, and why.
  8. Test the differenceChoose a test to compare cycles, check what it assumes, and state your significance level and sample sizes.
  9. EvaluateWhich weakness mattered most to your answer? Rank them. Make every improvement specific to what you found.
  10. Check before your teacher's draftRun the checklist below, then get your RQ or draft checked. Your teacher reads one draft only, so make it count.

Biology you'll need

Traps to avoid in this Biology IA

  • Cut surfaces leak pigment: if you don't rinse first, your 'zero cycle' is already high.
  • A ceiling effect: raw absorbance saturates, so use the boiled sample as 100 %.
  • Cubes of different size, so surface area changes between treatments.
  • Taking all cubes from one beetroot and claiming a general result.
  • Different thaw times between cycles, which becomes a hidden variable.
  • No blank on the colorimeter, or a different cuvette each time.

More Biology IA ideas like this

Make sure it's yours

This guide shows how a topic like this is usually approached. It is not an IA. Your question, choices, data, analysis and words must be your own: change something, tell your teacher where the idea came from, and follow your school's rules on outside help.

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