1. Chapter 11
Section 2

2. What are plant responses?
All organisms, including plants, respond to stimuli. (Plants respond to touch, gravity, and water)
Stimuli (Stimulus)- anything in the environment that effects the behavior of an organism (cause a response).

3. Tropisms
Tropism- response of a plant to an external stimuli. (when a pea plant touches a solid object, it grows faster on one side so it twists around any object it touches.)
Positive phototropism- plant grows toward light.

4. Tropisms
Gravitropism- plants response to gravity. The downward growth of plant roots is a positive response to gravity, a stem growing upward is a negative response to gravity.
Hormones control the changes in growth that result from tropisms and affect other plant growth.

5. Plant Hormones
Auxin-plant hormone that causes plant stems and leaves to exhibit positive responses to light. (grows toward the light)
Abscisic acid is a hormone that keeps seeds from sprouting and buds developing in the winter.
Photoperiodism- plant’s response to the number of hours of daylight and darkness it receives.

6. Plant Hormones
Long-day plants- requires less than 10 to 12 hours of darkness to flower (flower in late spring or summer)
Short-day plants- need 12 or more hours of darkness to flower (flowers in the late fall or winter)
Day-neutral plant- have no specific photoperiod.