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 ① Phototropism/Heliotropis m ② Hydrotropism ③ Geotropism/Gravitropism ④ Thigmotropism ⑤ 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 Venus Flytrap in Action • When temperatures become cold during the night a plant will close its leaves to keep itself warm • http: //www. youtube. com /watch? v=VUWQFF 0 RJN 4 • Thermotropism can be negative (cold) or positive (warmth)

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