About this experiment
Compare an intact shoot tip, a removed tip, an opaque tip cap and centred or one-sided auxin agar. Measure the two side lengths and connect unequal elongation to the bending direction.
Learning goals
- Separate tip light perception from auxin-induced elongation.
- Predict the direction of bending from unequal side lengths.
- Compare a treatment with a suitable symmetric control.
How to use it
- 1Run an intact tip with light from the right and inspect both side lengths.
- 2Cover the tip with an opaque cap and repeat the equal-duration trial.
- 3Remove the tip, then compare centred auxin agar with one-sided agar.
- 4Swap agar from left to right and check the mirrored bending direction.
The model
Assumptions
- An intact tip redistributes a fixed model auxin amount toward its shaded side. An opaque cap removes the light asymmetry while retaining symmetric endogenous auxin.
- All agar treatments replace the removed tip. A centred block supplies both sides equally; a side block supplies only its named side. Concentrations are relative model units.
- Shoot elongation increases with auxin through a specified saturating law, plus a residual auxin-independent rate. The rules do not describe roots or high-dose inhibition.
- The two sides begin at 3 cm and are separated by a 0.5 cm diameter. A uniform-curvature approximation relates side-length difference to angle.
- This is a schematic comparison of experimental controls, not a calibrated reconstruction of historical measurements.
Try this in class
- Q1Why does a longer left side bend the shoot toward the right?
- Q2Why does centred agar restore elongation without imposing a bend?
Frequently asked questions
Does the cap remove auxin?
No. In the model it blocks directional light perception while leaving equal endogenous auxin on both sides.
Can these results be applied to roots or arbitrary doses?
No. Auxin responses differ by tissue and dose. This model is explicitly limited to illustrative shoot elongation.