Tropisms

Stimulus Change in an organism’s surroundings that causes a response Internal (chemicals and hormones) External (light, touch, water, gravity) All living organisms, including plants, respond to stimuli

Response Reaction of a living thing to a stimulus

Stimulus/Response Response Stimulus

Internal Stimulus/Response Stimulus or response happens inside the organism Chemicals and hormones

External Stimulus/Response Stimulus or response occurs outside the organism Light, touch, water, gravity, electricity, temperature, darkness etc…

Tropism Automatic movement by an organism toward or away from a stimulus Positive (toward) Negative (away)

Phototropism When a plant or animal moves toward or away from light Positive – toward light Negative – away from light

Phototropism

Phototropism

Geotropism Also called gravitropism Plants or animals response to gravity Positive - roots growing down Negative - stems growing up

Geotropism

Geotropism http://plantsinmotion.bio.indiana.edu/plantmotion/movements/tropism/tropisms.html

Hydrotropism Directional movement toward water Usually occurs only in the roots

Hydrotropism

Thigmotropism When an organism responds to touch Vines Venus flytrap

Thigmotropism

Thigmotropism

Emergence of Seedlings Unbalanced forces allow seedlings to push their way through the soil and sometimes rock

Turgor Pressure Force in the form of pressure helps some plants stand upright. In animals, it also helps blood move around the body

Turgor Pressure

Turgor Pressure

emergence of seedlings thigmotropism phototropism geotropism organism’s response to light organism’s response to gravity organism’s response to touch hydrotropism turgor pressure emergence of seedlings organism’s response to water pressure inside the plant that allows it to stand up. seedling pushing up through the ground