• Phototropism:
  • Positive: Growth towards light (e.g., stems).
  • Negative: Growth away from light (e.g., roots).
  • What happens when a plant is illuminated from one side: It bends towards the light gradually.

Experiment: Effect of Unequal Distribution of Light on a Growing Shoot

• Objective: To investigate how unequal light distribution affects the growth direction of a shoot.

• Materials:

  • Two potted bean seedlings of similar growth stage
  • Cardboard box with a window cut on one side
  • Rotating clinostat (a device that rotates plants to provide even exposure to light)
  • Light source

• Method:

  1. Place one seedling inside the cardboard box, allowing light to enter only from the window on one side (unequal light distribution).
  2. Place the second seedling on a rotating clinostat, ensuring all sides of the shoot receive equal light exposure (control).
  3. Position both setups under the same light intensity and environmental conditions.
  4. Leave both seedlings for two days.

• Expected Results:

  • The seedling in the box with one-sided illumination will bend towards the light (phototropism).
  • The seedling on the clinostat will grow straight without bending since all sides receive equal light.

• Conclusion:

  • Unequal distribution of light causes the shoot to bend and grow towards the light source, indicating that light direction influences shoot growth. The shoot on the clinostat does not bend, confirming that equal light distribution prevents directional growth adjustments.