Tropisms. Stimulus Change in an organism’s surroundings that causes a response –Internal (chemicals and hormones) –External (light, touch, water, gravity)

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

Stimulus

Response

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

phototropism

turgor pressure

hydrotropismemergence of seedlings

thigmotropismgeotropism

organism’s response to

light

organism’s response to

gravity

organism’s response to

touch

seedling pushing up through the

ground

organism’s response to

water

pressure inside the plant that

allows it to stand up.