IB Biology IA idea · Environment and pollution
IB Biology IA idea: how salty can a seed stand?
Salty soil threatens crops and coasts. Find the point where germination starts to fail.
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 sodium chloride concentration (0, 50, 100, 150, 200 and 300 mmol dm⁻³) affect the percent germination of radish seeds after 5 days, from three dishes of 20 seeds at each concentration?
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
- salt (sodium chloride) concentration, 6 or more values from 0 to 300 mmol per dm3
- You measure
- percent germination after 5 days and mean radicle length, mm
- You keep the same
- same seed batch and number (25 or more per dish)
- same temperature and light
- same volume of solution
- same definition of germination
Method
Germinate cress or radish seeds on filter paper wetted with salt solutions and score germination daily. Measure root lengths on day 5.
Data analysis
Percent germination against concentration with standard deviation over at least 3 dishes, dose-response curve with the concentration at 50 percent, ANOVA. Link to water potential.
How it works
You change Salt concentration (mmol dm⁻³) and measure Seed germination (%) in Radish seeds on filter paper, keeping Seed batch, Dish size, Solution volume, Temperature the same. Expect a graph of Germination / % against Salt concentration / mmol dm⁻³: Germination should fall as salt rises.
Make it yours
Compare a salt-sensitive and a salt-tolerant species.
Extended Essay angle
Compare many crop species, or link to a database of crop salt-tolerance thresholds.
Safety
Do not eat seeds. Wash hands.
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