IB Biology IA idea · Plants and photosynthesis
IB Biology IA idea: how sucrose concentration affects pollen tube growth
A pollen grain grows a tube when it lands in the right place. In a dish, it needs the right sugar level.
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 sucrose concentration (0, 4, 8, 12, 16 and 20 %) of the germination medium affect mean pollen tube length (µm) after 2 hours, measured from microscope photographs of at least 30 tubes of one flower species?
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
- sucrose concentration of the germination medium, 0 to 20 percent, 6 or more values
- You measure
- mean pollen tube length after a fixed time, micrometres
- You keep the same
- same pollen source and age
- same incubation time and temperature
- same boron and calcium content of medium
- same slide-making method
Method
Dust fresh pollen from one flower type onto drops of sucrose-boric-acid medium, incubate and photograph under a microscope. Measure tube lengths on at least 30 grains per concentration.
Data analysis
Mean tube length and standard deviation per concentration, percent germination, bar or line graph; ANOVA or Kruskal-Wallis. Scale calibration with a micrometer slide.
How it works
You change Sucrose concentration (%) and measure Pollen tube length (µm) in Pollen of one flower species, keeping Incubation time, Temperature, Boric acid amount, Pollen source the same. Expect a graph of Mean pollen tube length / µm against Sucrose concentration / %: Look for an optimum before the medium becomes too strong.
Make it yours
Add a second medium variable such as boron, or compare two species.
Extended Essay angle
Relate optimum sugar concentration to species and pollination biology across a collection of flowers.
Safety
Pollen can trigger allergies: check with the teacher and avoid it if any student has hay fever.
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