IB Biology IA idea · Cells, division and structure
IB Biology IA idea: many small or few large guard cells?
Plants can make lots of small stomata or a few large ones. Test whether that trade-off is real.
These ideas are starting points, not an IA to copy. Never copy an idea blindly: make the question, method and analysis your own, and check your plan with your teacher.
Example research question
How does stomatal density (six species from 100 to 500 per mm²) affect guard cell length (µm), measured on 20 cells per species from clear-tape impressions under a light microscope?
Change the system, the range or the method so the question is yours. Check it against the research question checklist in our Biology IA guide.
Variables
- You change
- stomatal density, 6 or more species from 100 to 500 per mm2
- You measure
- guard cell length, micrometres
- You keep the same
- same leaf surface (lower)
- same leaf age and position
- same impression method
- same calibration
Method
Collect clear-tape or varnish impressions from leaves of different species and measure the length of 20 guard cells and the stomatal density for each. Calibrate with a micrometer slide.
Data analysis
Scatter graph of guard cell length against density (log-log), Spearman correlation, species means with standard deviations. Discuss phylogeny and environment as confounders.
How it works
You change Stomatal density (mm⁻²) and measure Guard cell length (µm) in Leaves of six species, keeping Leaf surface, Cells measured, Microscope scale the same. Expect a graph of Guard cell length / µm against Stomatal density / mm⁻²: Many small cells or few large ones.
Make it yours
Add leaf area or growing-site light to the analysis.
Extended Essay angle
Compare with published stomatal trait data across hundreds of species.
Safety
Take care with: work outdoors.
Take leaves with permission; use tape, not blades.
Data sources
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