Plants are sensitive to:
Phototropism- growth in response to light
Geotropism/gravitropism- growth in response to gravity
Positive tropism- growing towards the stimulus
Negative tropism- growing away from the stimulus
Auxin in Plants
Roots - towards moisture
-towards gravity = positive geotropism
Shoots - towards light = positive phototropism
- away from gravity = negative geotropism
Auxin - plant hormone that controls tropisms
Auxin is produced in the shoot or root tip, then travels to the target cells. It causes shoot cells to elongate, and inhibits elongation in root cells.
The unequal distribution of auxin causes unequal growth rates.
Plant growth hormones can be used in:
- Agriculture (growing crop plants in fields)
- Horticulture (growing flowers, fruit, and vegetable plants)
Plant hormones used in selective weedkillers. These kill weeds but don't harm the grass.
Plant hormones used in rooting powder- plant stems dipped in the powder develop roots more quickly.