Biology IA · C · Interaction and interdependence · topic 14 of 25

Enzyme beads: does size matter? · IB Biology IA idea: guide, sample graph and step-by-step plan

satisfying to watch, hard to control!

Trap an enzyme in a bead, then test whether bigger beads work more slowly. If they do, the maths of diffusion will explain why.

Difficulty●●○ Medium
KitCallipers, beakers, stopwatch, thermometer, catalase beads, 3% hydrogen peroxide
TimeAbout 10 hours
FitsSL and HL
  • ✓ you like making things and measuring them
  • ✓ you can make or buy beads
  • ✓ you like diffusion and surface area ideas

The big idea

← this is your RQ hook!

Hydrogen peroxide has to diffuse into the bead to meet the catalase, and oxygen bubbles make the bead float. A bigger bead has more enzyme, but its inside is further from the solution, and its surface area per unit volume is smaller. Your job: make beads of measured sizes, time how long each takes to rise, and decide what the pattern says about diffusion. It needs a design where size is the only thing you change, which is harder than it sounds.

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 →

Change the peroxide concentration

Repeat the series at two or three concentrations of hydrogen peroxide.

→ Tests whether diffusion or the enzyme limits the rate; the graph becomes a family of curves.
Change enzyme loading

Make beads with different amounts of catalase at one size.

→ Isolates the enzyme from the size effect; your independent variable becomes loading.
Break the beads

Compare whole beads with beads cut or crushed to the same mass.

→ Shows how much the barrier matters; the analysis compares two groups.
Use a different time measure

Measure the volume of oxygen collected in a syringe instead of the time to float.

→ A rate you can measure directly; the method and the units change.
Reuse the same beads

Test how the rate changes over several uses.

→ Adds a time variable and tests how stable the immobilised enzyme is. Needs enough beads.
Change the context

Link to industrial immobilised enzymes (lactose-free milk, for example).

→ Gives your range a purpose; the investigation stays the same.

Your Biology IA research question: run the check

write it FIRST, then check it

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

  • Names the independent variable (bead diameter) and the range and number of sizes.
  • Names the dependent variable (time to rise, and why it stands for rate) and defines start and finish exactly.
  • Says how you will make beads of different sizes while keeping enzyme concentration in the bead constant.
  • Says what stays fixed (peroxide concentration and volume, temperature, liquid depth) and how you check each.
  • Is narrow enough for about 10 hours, with at least five diameters and repeated beads at each.

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The set-up

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

dbead diameter d: measureeach bead, two waysO₂ bubbles liftthe beadstart timing at release,stop at the surfacesame volume of 3% H₂O₂,same temperature

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 immobilised enzymes are used in industry, and what you expect to happen and why.
Background biology~450
Catalase and hydrogen peroxide; diffusion into a sphere and how surface area to volume ratio changes with size; how you expect time to change with diameter (cite your source).
Variablestable
Independent, dependent and controlled variables, with how each is set, measured or kept constant, and why.
Method~450
How you made the beads and controlled their size; how you measured each; the release and timing; repeats; how you changed solution between runs.
Safety, ethics, environment~60
3% hydrogen peroxide irritates eyes and skin; use goggles and wash splashes. Disposal of alginate and enzyme.
Raw datatable
One clear table: each bead's diameter and time, units and uncertainties in the headers.
Processing~250
Mean diameter per bead, mean and spread of times, uncertainty in d² or other processed values, and one worked example of each calculation.
Graphs and analysis~350
The graph you choose and why, error bars, a fit justified by the data, and what the fit suggests about diffusion.
Conclusion~400
Answer the question with numbers and uncertainties, link to diffusion, and say how far the result applies.
Evaluation~600, the biggest part!
Weaknesses ranked by effect on your result (bead shape, uneven loading, temperature), and improvements linked to each.
Referencesnot counted
Every source for the biology and the bead method.

What your Biology IA graph could look like

error bars on EVERY point ✓

Made-up data, to show you the form of a strong graph, not the answer. Your beads, enzyme loading and numbers will differ. example only

23456789020406080100120140Bead diameter d / mm (± 0.1 mm)Time to rise t / s (mean ± SD, n = 5 beads)t proportional to d² (+ constant)straight linemean of 5 beads per size, with SDcurve or line? Compare bothwith your error barsILLUSTRATIVE · MADE-UP DATA
  • Both axes carry uncertainty: diameter from the callipers, time as the SD of the beads at each size. If the diameter uncertainty is small, say so and justify leaving out horizontal bars.
  • Each point is the mean of several beads of the same size. Show how many, and the spread.
  • A curve and a line are both shown so the reader can see which one the data follows, instead of assuming the straight line.
  • Say why the scale starts at zero for time: it shows how far the data sit from the origin.
  • Another graph to consider: plot log t against log d. If time rises as a power of diameter, the gradient is that power, and you can compare it with what diffusion predicts.

Which uncertainty matters most?

rank them: don't just list them

Rank by the effect on your result (d² at 5 mm; timing shown for comparison). If time depends on d², the diameter uncertainty counts double. Here the bead not being round matters most, so measure each bead in two directions and average.

Bead not round (±0.3 mm of 5 mm, squared)12%Callipers (±0.1 mm of 5 mm, squared)4%Timing the rise (±1 s of 60 s)1.7%biggest effect: discuss this first!% uncertainty in d² at 5 mmILLUSTRATIVE · MADE-UP NUMBERS

Your game plan

don't skip the trial run! it saves you weeks

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

0 of 10 done

  1. Read and predictFind out how beads are made and how time or rate should depend on size if diffusion is the limit. Write down your prediction before you start.
  2. Practise making beadsMake a small batch. Can you make beads of different sizes with the same mixture? How will you check they are round and that enzyme concentration is the same?
  3. Trial run (1 lesson)Drop a few beads into peroxide. Do all of them float, and does the time differ by size? Is the surface release repeatable? Fix the problems now.
  4. Decide range, repeats and timingChoose at least five diameters, how many beads at each, and exactly when you start and stop timing. Write down why for each choice.
  5. Measure every beadMeasure each bead's diameter before use, in two directions, and record it with its run.
  6. Collect the dataRecord each time straight into your table. Use fresh peroxide of the same concentration each run, and control temperature.
  7. ProcessCalculate the mean diameter and mean time for each size, with uncertainties. Decide how the diameter uncertainty carries into your result.
  8. Graph and fitPlot with error bars. Compare a straight line with a curve and decide which the data support.
  9. EvaluateWhich weakness mattered most? Use your own scatter and bead measurements to rank them. Make every improvement specific.
  10. Write, then checkWrite in the order of the layout. Run the checklist below before your teacher's draft.

Biology you'll need

Traps to avoid in this Biology IA

  • Beads that are not round or that stick together: diameter is then not one number.
  • Making big beads from a different mixture, so size and enzyme concentration change together.
  • Fresh peroxide not used each time, or a peroxide solution that has decayed during the day.
  • Starting the clock at different moments (dropped, touched the bottom, left the hand).
  • Beads that stick to the glass, or wait at the bottom with a bubble that has not released them.
  • No uncertainty on diameter, although it is the variable you set.
  • Saying 'diffusion explains it' without a calculation, a reference or a test.

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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