1. Plant “Behavior”

2. Plant “Behavior” How do roots “know” to grow down?
How do stems “know” to grow up?
Chemicals (hormones) that control, direct, and regulate plant growth
Hormone: substance produced in one part of an organism and affects another part of the same individual

3. Plant Hormones
Auxins – stimulate cell elongation (growth upward and downward)
Cytokinins – stimulate cell division and growth of lateral buds (sideways growth)
Cause dormant seeds to sprout
Gibberellins – produce dramatic increases in size (particularly in stems and fruit)
Ethylene – stimulates fruit to ripen

4. Plant Responses Tropisms – plant responses to external stimuli
Gravitropism: plant response to gravity
Involves auxins
Phototropism: plant response to light
Thigmotropism: plant response to touch

5. Nastic Movements
Plant movements that occur in response to environmental stimuli but unlike tropic movements, the direction of the response is not dependent on the direction of the stimulus
Example: Venus fly trap

6. Photoperiodism
Responsible for the timing of seasonal activities, such as flowering and growth
Regulated by a pigment that absorbs red light