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 include① Phototropism/Heliotropism② Hydrotropism③ Geotropism/Gravitropism④ Thigmotropism⑤ 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