IB Biology IA ideas: 25 research questions that work in a school lab

The best IB Biology IA ideas test one relationship you can measure with school equipment: one independent variable set at five or more levels, one dependent variable you record as a number, and the other variables held steady. Below are 25 ideas sorted by syllabus topic, each written as a full research question with its range, method, key controls and the trap that most often costs marks. Change the organism, the range or the context so that the question becomes yours.

To sharpen your own question, read how to write an IA research question; for a finished report, see the annotated science IA example.

Which enzyme investigations make good IAs (C1.1)?

1. Temperature and catalase activity

RQ: How does temperature (10, 20, 30, 40, 50 and 60 °C) affect the initial rate of oxygen production by catalase in potato (Solanum tuberosum) extract, measured as the volume of oxygen collected in a gas syringe in the first 30 s?

• Method: rate in cm³ s⁻¹ and Q₁₀ (rate at T + 10 °C ÷ rate at T) below the optimum. Control peroxide concentration, extract batch and buffer pH.
• Trap: cold extract added to warm substrate runs at neither temperature. Equilibrate both tubes separately, and run a no-enzyme tube at each temperature, because peroxide also decomposes faster on its own when warm.

2. pH and amylase activity

RQ: How does pH (4.0, 5.0, 6.0, 7.0 and 8.0) affect the rate of starch hydrolysis by fungal amylase at 30 °C, measured as the time taken for 1% starch solution to stop giving a blue-black colour with iodine?

• Method: spotting tile every 30 s; rate = 1 ÷ time. A colorimeter reading at a fixed time beats judging colour by eye.
• Trap: a different buffer chemical at each pH adds a second variable; one citrate–phosphate buffer covers the whole range. Fungal, bacterial and salivary amylases have different optima, so compare with values for your source.

3. Substrate concentration and catalase (floating discs)

RQ: How does hydrogen peroxide concentration (0.25, 0.5, 1.0, 1.5, 2.0 and 3.0%) affect the rate of reaction of catalase in yeast (Saccharomyces cerevisiae) suspension, measured as the time for a filter-paper disc soaked in the suspension to rise through 5 cm of solution?

• Method: rate = 1 ÷ time, five discs per concentration, fixed soaking time and depth.
• Trap: the rate levels off as active sites saturate, so a straight-line fit is wrong; put extra concentrations at the low end. Stir the yeast before every disc, because it settles within minutes.

4. Enzyme concentration and protein digestion

RQ: How does trypsin concentration (0.2, 0.4, 0.6, 0.8 and 1.0%) affect the rate of casein hydrolysis in a 2% skimmed-milk-powder suspension at pH 8 and 35 °C, measured as the fall in absorbance in a colorimeter over the first 60 s?

• Method: the suspension clears as casein is digested; initial rate = change in absorbance per second.
• Trap: the top concentrations can clear too fast to follow, so pilot the range. Rate is proportional to enzyme concentration only while substrate is in excess. Trypsin powder is a respiratory sensitiser, so use ready-made stock solutions.

5. Pectinase and juice yield

RQ: How does pectinase concentration (0, 0.5, 1.0, 1.5 and 2.0% v/v) affect the volume of juice filtered in 10 minutes from 50 g of puréed apple (one named cultivar) incubated for 15 minutes at 40 °C?

• Method: filtrate volume; control blending time, incubation and filter paper.
• Trap: enzyme solution adds liquid too, so top every beaker up to the same added volume and include a boiled-enzyme control.

What can you investigate with water potential and membranes?

These build on D2.3 and B2.1. Keep the direction straight: water moves from higher to lower (more negative) water potential, and adding solute lowers water potential.

6. Water potential of potato tissue

RQ: How does sucrose concentration (0.0, 0.2, 0.4, 0.6, 0.8 and 1.0 mol dm⁻³) affect the percentage change in mass of potato (one named variety) cylinders after 24 h at 20 °C, and what concentration is isotonic with the tissue?

• Method: % change = (final − initial) ÷ initial × 100, five cylinders per solution; the isotonic point is where the best-fit line crosses zero, with an uncertainty.
• Trap: the plain version is the most-repeated Biology IA. Make the isotonic point the result and compare two varieties, or new and stored potatoes. Blot every cylinder the same way; inconsistent blotting is often the largest error.

7. Plasmolysis in onion epidermis

RQ: How does sucrose concentration (0.0 to 0.8 mol dm⁻³ in 0.1 mol dm⁻³ steps) affect the percentage of plasmolysed cells in red onion (Allium cepa) epidermis after 15 minutes, counted in three fields of view of at least 30 cells each?

• Method: find the concentration giving 50% plasmolysis (incipient plasmolysis). There pressure potential is about zero, so the cells' solute potential roughly equals the solution's water potential.
• Trap: write down before you start what counts as plasmolysed (for example, membrane visibly pulled away from the wall in at least one corner), or you will count what you expect to see.

8. Temperature and membrane permeability in beetroot

RQ: How does temperature (20, 30, 40, 50, 60 and 70 °C) affect the permeability of beetroot (Beta vulgaris) cell membranes, measured as the absorbance at about 530 nm of the water around six discs after 30 minutes?

• Method: absorbance rises as red betalain pigment leaks out. First rinse the discs until the water stays clear, to remove pigment from cut cells.
• Trap: absorbance stops being proportional to concentration at high values, so dilute the darkest samples and record the dilution. A variant uses ethanol concentration (0–50%) at constant temperature; keep ethanol away from flames.

Which photosynthesis and respiration ideas work?

Ideas 9 to 11 build on C1.3, 12 and 13 on C1.2.

9. Light intensity and photosynthesis in leaf discs

RQ: How does light intensity (LED lamp at 10, 15, 20, 25, 30 and 40 cm, measured in lux at the discs) affect the rate of photosynthesis of spinach (Spinacia oleracea) leaf discs in 0.2% sodium hydrogencarbonate solution, measured as the time for 5 of 10 discs to float?

• Method: rate = 1 ÷ time. Discs rise as oxygen collects in the air spaces, so this measures net photosynthesis (photosynthesis minus respiration).
• Trap: do not assume intensity follows 1 ÷ distance²; a lamp this close is not a point source. Measure light at the discs every time, and use an LED so the lamp does not warm the solution.

10. Carbon dioxide concentration and pondweed

RQ: How does sodium hydrogencarbonate concentration (0, 0.1, 0.2, 0.4, 0.6, 0.8 and 1.0% w/v) affect the rate of gas production by a pondweed (such as Elodea or Egeria), measured as the length of the gas bubble collected in a capillary tube in 5 minutes?

• Method: bubble length converted to volume using the bore; same sprig throughout, 5 minutes' acclimatisation per concentration.
• Trap: bubble size varies, so collect the gas rather than counting bubbles. The rate levels off when light becomes limiting; that is a result, not an error. Several pondweeds are legally restricted as invasive species (Elodea nuttallii, for example, cannot be sold or kept anywhere in the EU), so use what your school is allowed to keep and never release plants into waterways.

11. Light colour and photosynthesis

RQ: How does light wavelength (five narrow-band LEDs between about 450 and 630 nm) affect the rate of photosynthesis of spinach leaf discs, measured as the time for 5 of 10 discs to float?

• Method: as idea 9, at a fixed distance and equal light intensity at the discs.
• Trap: lux meters weight light by how bright it looks to the eye, which peaks in green, so equal lux is not equal photon numbers. Use a PAR (quantum) meter if you can, or state the limitation. Leaves absorb less green light, not none.

12. Temperature and yeast respiration

RQ: How does temperature (15, 20, 25, 30, 35, 40 and 45 °C) affect the rate of carbon dioxide production by Saccharomyces cerevisiae in 5% glucose solution, measured with a CO₂ sensor over 10 minutes after 5 minutes' equilibration?

• Method: rate of CO₂ production and Q₁₀ below the optimum; one packet of yeast, one rehydration method.
• Trap: the sensor cannot separate aerobic from anaerobic respiration, so word your conclusion accordingly. CO₂ is less soluble in warm water, so more reaches the sensor at high temperatures; evaluate this.

13. Sugar concentration and yeast respiration

RQ: How does glucose concentration (0, 2, 5, 10, 15, 20 and 30%) affect the rate of carbon dioxide production by Saccharomyces cerevisiae at 30 °C?

• Method: as idea 12, with temperature fixed.
• Trap: at high concentrations the low water potential draws water out of the cells and the rate may level off or fall. That is a link to D2.3, not an anomaly, so extend the range far enough to see it.

How do you run a safe microbiology IA?

Follow your school's culturing rules: approved non-pathogenic strains only, aseptic technique, incubation at no more than about 30 °C, lids taped but not sealed all round, plates never opened after incubation, everything sterilised before disposal. Ask your teacher before you plan anything.

14. Garlic extract and bacterial growth

RQ: How does the concentration of fresh garlic (Allium sativum) extract (0, 10, 25, 50, 75 and 100%) affect the diameter of the zone of inhibition of Bacillus subtilis after 48 h at 25 °C?

• Method: zone diameter minus disc diameter, two perpendicular readings per disc, several discs per concentration across several plates.
• Trap: allicin, the main antibacterial compound, forms when garlic is crushed and then breaks down. Make one stock and dilute it straight away.

15. Milk storage temperature and microbial activity

RQ: How does storage temperature (4, 10, 15, 20 and 25 °C for 48 h) affect the microbial activity of pasteurised whole milk, measured as the time for resazurin added to the milk to change from blue to pink at 30 °C?

• Method: microbes reduce the dye, so a shorter time means more activity.
• Trap: the colour change is gradual, so use reference tubes for the end point or a colorimeter. Treat the milk as a culture: never taste it.

16. pH and yeast population growth

RQ: How does initial pH (4, 5, 6, 7 and 8) of a glucose growth medium affect the population growth rate of Saccharomyces cerevisiae over 48 h at 25 °C, measured as live-cell density using a haemocytometer and methylene blue staining?

• Method: counts at 0, 6, 12, 24, 30 and 48 h; growth rate from the gradient of ln(cell density) against time in the exponential phase (C4.1).
• Trap: counting is slow and easy to bias: dilute to a countable density, count the same squares every time, and fix a rule for cells on the edges. Methylene blue stains dead cells, so count only unstained ones.

Which plant physiology ideas are worth doing?

17. Air movement and transpiration

RQ: How does air speed (0, 1, 2, 3 and 4 m s⁻¹, measured with an anemometer at the leaves) affect the rate of water uptake by a leafy shoot of one named species, measured with a bubble potometer and expressed per cm² of leaf area?

• Method: bubble movement converted to volume, divided by leaf area traced on squared paper (B3.2). Same shoot throughout, 10 minutes' acclimatisation; record humidity.
• Trap: cut and fit the shoot under water, or air blocks the xylem. A potometer measures uptake, not loss; say so.

18. Stomatal density in sun and shade leaves

RQ: How does light exposure (fully sunlit versus fully shaded leaves of the same plant) affect stomatal density (stomata mm⁻²) on the lower surface of ivy (Hedera helix) leaves, using nail-varnish impressions of 15 leaves per group and 3 fields of view per leaf?

• Method: stomata per field ÷ field area, after calibrating the field diameter with a stage micrometer (area = πr²). Match leaf age and position on the leaf (B3.1).
• Trap: two groups need many replicates and a statistical test (t-test or Mann–Whitney U; see which statistical test to use). Better: measure light at each leaf and test a correlation.

19. Salinity and seedling growth

RQ: How does sodium chloride concentration (0, 25, 50, 75, 100 and 150 mmol dm⁻³) affect the mean root length of cress (Lepidium sativum) seedlings after 72 h at 20 °C, with 20 seeds per dish and 3 dishes per concentration?

• Method: measure every root, by ruler or from a photo with a scale.
• Trap: evaporation raises the salt concentration, so seal the dishes. Decide in advance how to record seeds that do not germinate.

20. Nitrate and duckweed population growth

RQ: How does nitrate concentration (0, 5, 10, 20, 40 and 80 mg dm⁻³, as potassium nitrate in a nitrogen-free nutrient solution) affect the relative growth rate of Lemna minor, measured as frond number over 14 days?

• Method: relative growth rate = (ln N₂ − ln N₁) ÷ (t₂ − t₁), from counts every two days.
• Trap: tap water contains nitrate, so use deionised water plus a nitrogen-free base medium. Define when a daughter frond counts.

What makes a good ecology or database IA?

Fieldwork and databases trade control for realism, so measure the variables you cannot hold constant. The ecology field IA guide covers sites, sampling and quadrats.

21. Trampling and plant diversity

RQ: How does distance from a footpath (0, 0.5, 1, 2, 3 and 4 m) affect plant species richness and Simpson's diversity index in 0.25 m² quadrats along eight randomly placed transects at one named park?

• Method: species and percentage cover per quadrat, plus soil compaction (a penetrometer, or the time for a fixed volume of water to soak in).
• Trap: path edges differ in more than trampling (light, dog nutrients, mowing). Measuring compaction links the mechanism directly.

22. Light under a canopy and ground flora

RQ: How does relative light intensity at ground level affect the percentage cover of one named ground-flora species in 30 randomly placed 0.25 m² quadrats in one named woodland?

• Method: lux at each quadrat as a percentage of an open-ground reading taken at the same moment; Spearman's rank correlation.
• Trap: light changes as clouds pass, hence the simultaneous open-ground reading. Measure soil moisture and pH too.

23. Spring temperature and flowering date (database)

RQ: How does mean March–April temperature correlate with the first-flowering date of one named species in one named region over at least 20 years, using records from a public phenology database and a national weather record?

• Method: flowering day of the year against temperature; the regression gives days per °C to compare with published climate-change work (D4.3).
• Trap: a database IA still needs a method: justify your filtering rules (sites, records per year, earliest or median date). More observers produce earlier "first" dates by chance, so a median is safer. Download the data before you commit.

Can you do a human physiology IA ethically?

Yes, with volunteers doing everyday-level activity only: written informed consent, the right to withdraw, exclusion of anyone with a medical reason not to take part, and anonymised data. Your school may also require parental consent.

24. Exercise intensity and heart-rate recovery

RQ: How does stepping rate (15, 20, 25 and 30 steps per minute for 3 minutes on a 30 cm step, paced by a metronome) affect heart-rate recovery time in 12 healthy 16–18-year-old volunteers?

• Method: pulse oximeter or chest strap; recovery time = time to return within 5 beats per minute of resting rate.
• Trap: fitness differs between people far more than the effect you are testing, so every participant does every rate, in random order, and you analyse the change within each person.

25. Background noise and reaction time

RQ: How does background noise level (a quiet room, 50, 60 and 70 dB of recorded traffic noise, measured at ear level) affect mean simple visual reaction time on an online reaction-time test, in 15 volunteers tested at every level?

• Method: mean of 10 reaction times per level on the same device and browser (C2.2 links this to neural signalling). Keep noise comfortable and well below harmful levels.
• Trap: practice makes people faster, so give practice trials and randomise the order of noise levels.

How can you tell whether an idea can reach the top bands?

The Biology guide says the investigation needs enough extent and depth for every criterion to be addressed meaningfully. Check five things before you commit:

Then pilot the two extreme levels, twice each. If their difference is not clearly bigger than the spread of repeats, change the range or method now. What each criterion rewards is set out in our guide to the science IA criteria.

What ethics and safety rules apply?

You must consider safety, ethical and environmental issues before collecting data, and Research design credits them, so write them into your method.

• Animals: plan nothing that causes an animal pain, stress or harm, including dosing invertebrates with drugs. Use plants, microbes, enzymes or observation, and get your teacher's approval before involving any animal.
• Humans: anything involving body fluids, medicines, supplements or diet changes needs explicit school approval and is often not allowed.
• Environment: get permission for field sites, do not uproot or remove organisms, and dispose of chemicals and cultures as your school requires.