Warm Up # Why is it sometimes hard to see a plant’s response to a stimulus?

Plant Responses

Essential Questions How do plants respond to environmental stimuli? How do plants respond to chemical stimuli?

How do plants respond to stimuli? ACTIVITY Take a pot of young radish seedlings and place toothpicks parallel to a few of them Place pot near a light source so that it’s to one side of the pot Check position of the seedlings in relation to the toothpicks after 30 mins. What did you notice? What did it look like after a day?

Stimuli and Plant Responses Stimuli – any changes in an organism’s environment that cause a response can be slow (plant growing toward light) or quick (Venus flytrap’s response to touch) Responds to external (light, touch, and gravity)and internal (hormones) stimuli BrainPOP – Plant Growth

Environmental Stimuli Growth Responses Tropism – a response that results in plant growth toward or away from a stimulus Positive – towards the stimulus Plant bending toward light Negative – away from the stimulus Plant stem growing upward against gravity Phototropism – plant growing toward or away from light Maximizes the amount of light the plant gets

Environmental Stimuli Growth Responses Thigmotropism – plant’s response to touch Gravitropism – plant’s response to gravity Stems grow up, roots grow down

Environmental Stimuli Flowering Responses Photoperiodism – plant’s response to the number of hours of darkness in its environment Long-day plants: flower when exposed to less than 10-12 hours of darkness; flower in summer Short-day plants: require 12 or more hours of darkness; flower late summer/early fall Day-neutral plants: flower when reach maturity and conditions are right

Chemical Stimuli Plant hormones – substances that act as chemical messengers within plants Auxin – cause increased plant growth toward the light Ethylene – helps stimulate the ripening of fruit that’s produced by fruits, seeds, flowers, and leaves

Chemical Stimuli Gibberellins – increases the rate of cell division and cell elongation; increases growth of stems and leaves Cytokinins – increases the rate of cell division and in some plants slow the aging process of flowers and fruits; found in roots

Humans and Plant Responses