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

2. 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.

3. 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.

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

5. 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

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

7. 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

8. 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

9. 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

10. 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

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

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

13. 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

14. 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

15. 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

16. 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

17. 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)

18. 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

19. 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)

20. 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.

21. 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.

22. 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