1. Plant Responses to the Environment

2. Tropism Plant growth or bending towards or away from a stimulus
Positive tropism – to turn towards a stimulus
Negative tropism – to turn away from a stimulus

3. Phototropism The growth of a plant in response to light
Stems move towards the light (positive phototropism)
Roots move away from light (negative phototropism)

4. Geotropism The growth of a plant in response to gravity
Stems and leaves grow away from Earth (negative geotropism)
Roots grow towards Earth (positive geotropism)

5. Hydrotropism A plant’s growth or bending in response to water
Roots grow towards water (positive hydrotropism)

6. Thigmotropism The way a plant grows or bends in response to touch
Vines grow up buildings or wrap around objects (positive thigmotropism)
Roots grow away from objects in soil (negative thigmotropism)

7. Chemical Stimuli
Plant hormones are substances that act as chemical messengers within plants
Auxin – a hormone that builds up on the dark side of a stem and lengthen that side causing plants to grow toward light

8. Seasonal Changes
Photoperiodism - a plant’s response to the number of hours of darkness in its environment
Determines when plants flower
Long-Day Plants flower during summer when nights are short
Short-Day Plants flower in fall and winter when nights are long

9. Seasonal Changes
Dormancy – a period when an organism’s growth or activity stops.
This helps plants survive harsh winter conditions