Plant ProcessesPlant Processes88thth 15.2 Plant Responses 15.2 Plant Responses

Plant ResponsesPlant Responses Tropism – response of a plant to an Tropism – response of a plant to an

outside stimulusoutside stimulus Stimulus that affects a plants Stimulus that affects a plants

growthgrowth Light, heat, moisture, gravity, Light, heat, moisture, gravity,

electricity, touch and chemicals.electricity, touch and chemicals. Positive - grows toward stimulusPositive - grows toward stimulus Negative – grows away from Negative – grows away from

stimulusstimulus

Plant ResponsesPlant Responses

Plant ResponsesPlant Responses PhototropismPhototropism GravitropismGravitropism ThigmotropismThigmotropism Auxin – plant hormone that Auxin – plant hormone that

lengthens cellslengthens cells Ethylene – plant hormone that Ethylene – plant hormone that

causes fruit to ripencauses fruit to ripen

Plant ResponsesPlant Responses

Plant ResponsesPlant Responses Photoperiodism – plants response to Photoperiodism – plants response to

the number of hours of daylight and the number of hours of daylight and nightnight

Long day plants - petunias, lettuce, Long day plants - petunias, lettuce, wheat, barley, carnation, radish, wheat, barley, carnation, radish, tobaccotobacco

Short day plants – onion, sugar cane, Short day plants – onion, sugar cane, blueberry, rhododendron, marijuanablueberry, rhododendron, marijuana

Day neutral plantsDay neutral plants

Plant ResponsesPlant Responses