Question

Bending of stem/coleoptile towards light or shoot of potted plant placed near a window is due to

• A. Greater oxygen availability to the tip
• B. More auxin content on the shaded side
• C. Availability of necessary warmth to the tip
• D. Greater light availability to tip

Answer 1

The correct option is B More auxin content on the shaded side

Charles Darwin and his son Francis Darwin observed that the coleoptiles of canary grass bend towards light.
Coleoptile is a protective sheath of the emerging shoot apex in the monocot embryo.
They observed that when unidirectional light falls on the coleoptile, it bends in the direction of the light source (phototropism).
Growing tip when illuminated with light, leads to the transportation of auxin to the shady region creating a concentration gradient.
The cells in the shady region elongate faster when compared to its opposite side due to greater localisation of auxin. This results in the bending of the tip away from the shady region and towards the direction of light.