Investigate the effect of IAA growth regulator on plant tissue (LC 2026) (Leaving Cert Biology): Revision Notes

Investigate the effect of IAA growth regulator on plant tissue

Growth regulators at different concentrations affect plant growth. For the growth regulator IAA:

• At low concentrations, IAA encourages root growth and inhibits shoot growth.
• At high concentrations, IAA encourages shoot growth and inhibits root growth. In this experiment, seeds are used as the plant tissue. The control is a petri dish with seeds treated with distilled water instead of IAA.

Materials needed:

• 8 petri dishes
• 8 bottles
• IAA (Indole acetic acid) solution
• Distilled water
• Droppers
• Circular acetate grids
• Radish seeds
• Philtre paper
• Cotton wool
• Incubator set at 25°C
• Measuring tools (ruler)
• Labels

Method:

1. Label 8 petri dishes and 8 bottles as shown in the diagram.

2. Add 10 cm³ of the IAA solution to the first bottle.

3. Add 9 cm³ of distilled water to each of the next seven bottles.

4. Remove 1 cm³ of the IAA solution from the first bottle and add it to the second bottle.

5. Remove 1 cm³ of the solution from the second bottle and add it to the third bottle.

6. Repeat this serial dilution procedure for the fourth, fifth, sixth, and seventh bottles, using a different dropper each time.

7. Discard 1 cm³ of solution from the seventh bottle so that each bottle contains 9 cm³ of solution.

8. Fit a circular acetate grid inside the lid of each petri dish. Acetate grid is lined and will make measuring root and shoot length easier.

9. Place five radish seeds in each dish as shown in the diagram.

10. Place a philtre paper and cotton wool on top of the seeds in each dish.

11. Add each solution to its matching dish.

12. Stand the dishes vertically on their edge to ensure the roots grow downward.

13. Place the dishes in the incubator for 2-3 days at 25°C to allow germination.

14. Measure and record the length of the roots and shoots of the seedlings in each dish.

15. Calculate the percentage stimulation or inhibition of root and shoot growth in each dish using the formula:

    

16. Draw a graph of percentage stimulation and inhibition of root and shoot growth against IAA concentration. Note: The 8th bottle acts as the control.

Results:

• Low IAA Concentration: Roots grew, but shoots did not.
• High IAA Concentration: Shoots grew, but roots did not.
• Control: Both roots and shoots grew equally.