About this experiment
Grow a shoot under directional light, then move the light and observe a new growth direction. Compare light response, gravity response and initial tilt while retaining the path formed before a lamp switch.
Learning goals
- Distinguish directional growth from rotating a completed plant.
- Compare phototropic turning with upward gravitropic turning.
- Design a before-and-after light-switch trial.
How to use it
- 1Grow the shoot for 24 hours with side lighting.
- 2Switch light now and continue growth to the opposite side.
- 3Turn off the phototropic response and repeat.
- 4Begin with a tilted shoot in darkness and compare the effect of gravity.
The model
Assumptions
- A two-dimensional growing tip extends at a constant selected rate. Its angular velocity combines a sine response toward the lamp with a sine response toward vertical.
- A fixed 0.1-hour RK4 scheme integrates both direction and position, splitting a step exactly at the scheduled lamp switch.
- One switch is supported. Its pre-switch centreline remains fixed; only subsequent tip growth follows the new light.
- Response coefficients, geometry and growth rate are illustrative. Auxin transport, tissue mechanics, circumnutation and growth-zone redistribution are not resolved.
- Editing a scheduled switch compares alternative histories. The immediate switch action uses the current time and is disabled once that event has been applied.
Try this in class
- Q1Why should an old lower segment stay put after the lamp changes sides?
- Q2How can gravity and light compete to set a nonvertical growing direction?
Frequently asked questions
Does changing light rotate the whole shoot?
No. A scheduled switch changes future growth direction while retaining the preceding centreline.
Is this an auxin-transport simulation?
No. It is a stated directional-growth model. The separate hormone experiment compares simplified differential elongation treatments.