Plant Responses to the Environment

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

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

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)

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

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)

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

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

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