How Plants Respond to External Stimuli Plant Behaviors How Plants Respond to External Stimuli

Essential Standards 6.L.2 Understand the flow of energy through ecosystems and the responses of populations to the biotic and abiotic factors in their environment.

Clarifying Objectives 6.L.2.2 Explain how plants respond to external stimuli (including dormancy and forms of tropism) to enhance survival in an environment.

Essential Questions How do plants adapt to environmental conditions? Why do plants adapt to environmental conditions? What is dormancy? What are Tropisms?

Evolution of Plants Plants have evolved over thousands of years Plants now have the ability to grow TOWARDS vital resources like sunlight, water & nutrients This evolution of plants helps to ensure that they survive

Essential Questions Get with a partner and answer… Why do plants adapt to environmental conditions?

External Stimuli External Stimuli is anything in a plants environment that will cause it to physically react External Stimuli include Temperature Sunlight Being Touched Chemicals Gravity Water

Dormancy (Unfavorable Conditions) Dormancy is the other way plants respond to External Stimuli Dormancy is when a plant stops growing and reserves its energy for better conditions The plant or seed is not dying it is simply saving its growing power

Dormancy (Unfavorable Conditions) Dormancy happens when plants experience growing conditions in which they will be unsuccessful & die An example of this is flowers in the winter The seeds lie dormant in the winter and then come up when it gets warm again

Tropisms Tropisms are the other way plants respond to external stimuli Positive Tropisms are plant responses in the direction toward the External Stimulus Negative Tropisms are responses in the opposite direction of the External Stimulus

Tropisms Tropisms are advantageous to the plant because they support the organism well being

Essential Questions Get with a partner and answer… How do plants adapt to environmental conditions? What is dormancy? What are Tropisms?

Tropisms There are many different tropisms depending on what External Stimuli the plant is behaving towards Some examples of tropisms include Phototropism/Heliotropism Hydrotropism Geotropism/Gravitropism Thigmotropism Thermotropism

Phototropism (Sunlight) Phototropism is the plants response to light (sun) The plant will change direction and grow toward the sunlight Positive phototropism is when the plant begins adjusts itself to make sure it gets sunlight

Phototropism (Sunlight) Plants & trees will go to major lengths to make sure they get enough light Without light plants cannot go through photosynthesis This means that they will not be able to make their own food and will therefore die

Hydrotropism (Water) Hydrotropism is when plants respond to by their roots extending toward a lake or river Positive Tropism Hydrotropism occurs because a plant or tree is not getting enough water

Geotropism/Gravitropism Geotropism & Gravitropism are the same thing This is the plants response to gravity The plant will either want to grow upward toward the sky (positive) The plant might want to grow downward toward the ground (negative)

Thigmotropism (Touch) Thigmotropism is a plants reaction to touch It is a defense reaction to preserve its leaves Negative Tropism During Thigmotropism the plants leaves will quickly close up when they are touched

Thermotropism (Temp) Thermotropism is a plant or tree’s response to different temperatures When temperatures become cold during the night a plant will close its leaves to keep itself warm Thermotropism can be negative (cold) or positive (warmth) http://www.youtube.com/watch?v=VUWQFF0RJN4

EOG Questions A plant begins to bend when a tall building is built near it. Why does this occur? A) It is adjusting to changes in the temperature. B) It is growing away from the light source. C) It is adjusting to changes in the soil. D) It is growing toward the light source.

EOG Questions Why do seeds go through a period of dormancy? A) It allows time for the right conditions to occur before the seed germinates. B) It allows time for dry soil to accumulate before the seed germinates. C) It allows time for sunlight to appear before the seed germinates. D) It allows time for pollination to occur before the seed germinates.

Important Points Tropisms & dormancies are evolutions of a plant meant to enhance survival External Stimuli from the plant’s environment influence the plant to make changes Dormancies are reactions by a plant or seed to unfavorable growing conditions Tropisms are reactions by the plant to its environment Positive Tropisms are movements by a plant toward the External Stimuli Negative Tropisms are movements away from the External Stimuli