1. Session 74: 6.L.2.2 Explain how plants respond to external stimuli (including dormancy and forms of tropism) to enhance survival in an environment.
Changes in environmental conditions can affect the survival of individual organisms and entire species.
Dormancy is a period of inactivity in a mature seed prior to germination; seed remains dormant until conditions are favorable for growth and development of the new plant.
Plants have mechanisms that enable them to respond to their environment.
Plants grow, reproduce, and shift the position of their roots, stems and leaves in response to environmental conditions such as gravity, sunlight, temperature and day length.
Tropism is a plant’s turning or bending movement toward or away from an external stimulus such as light, heat or gravity.
If the tropism is positive, the plant grows toward the stimulus.
If the tropism is negative, the plant grows away from the stimulus. This enhances the survival rate for that plant in a given environment.
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2. Warm Up
1. What is this bat doing?
2. Notice the location of the stamens in this flower. How does their location ensure the reproduction of this plant?

5. Changes in environmental conditions can affect the survival of individual organisms and entire species.

6. Dormancy is a period of inactivity in a mature seed prior to germination; seed remains dormant until conditions are favorable for growth and development of the new plant.

7. Dormancy can happen to mature plants as well; when growth and activity are temporarily stopped, usually due to environmental conditions.
When do plants go dormant?

8. Plants have mechanisms that enable them to respond to their environment.
Plants grow, reproduce, and shift the position of their roots, stems and leaves in response to environmental conditions such as gravity, sunlight, temperature and day length.

9. TROPISM- There are many types of tropisms : Phototropism Geotropism
Tropism is a plant’s turning or bending movement of an organism toward or away from an external stimulus such as light, heat or gravity.
(“tropo” – ”turn”)
There are many types of tropisms :
Phototropism
Geotropism
Thigmotropism
Hydrotropism
Chemotropism
Thermotropism .
3 main types
If the tropism is positive, the plant grows toward the stimulus.
If the tropism is negative, the plant grows away from the stimulus.
Is the plant above responding positively toward sunlight?
What about gravity?
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10. Ex. Stems growing toward the window to get to the light
PHOTOTROPISM
(“Photo” – light)
The growth response of a plant in response to light direction is called phototropism.
Ex. Stems growing toward the window to get to the light
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11. IMPORTANCE OF PHOTOTROPISM
Enables leaves to be in the best position possible to receive adequate light for photosynthesis
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12. Geotropism is the growth of a plant in response to gravity.
(“Geo” – Earth)
Geotropism is the growth of a plant in response to gravity.
Negative Geotropism
Positive Geotropism
It is the growth of a plant towards the center of the earth-down with gravity.
Ex. roots growing down
Negative Geotropism
It is the growth of a plant away from the center of the earth-opposite from the pull of gravity
Ex. stems grow up
Positive Geotropism
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13. IMPORTANCE OF GEOTROPISM
Pulls roots down to anchor a plant
Roots can get needed water and
minerals if they stay in the soil
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14. CORN TROPISM LAB

15. Thigmotropism is the growth of a plant in response to touch/contact.
(“Thigmo” – “touch”)
Thigmotropism is the growth of a plant in response to touch/contact.
Photo by Christopher Meloche
Tendrils on a sweet pea
Discovery Ed Clip on Plants Responsive to Touch
Vines growing on a wall or fence
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16. All of this enhances the survival rate for that plant in a given environment.

17. Time for a StudyJam on Plant Adaptations:

18. Written Response#1:
A plant is placed on a windowsill facing the sun. After a week, the plant is rotated away from the sun. How will the plant most likely respond?

20. SOME OTHER
TYPES OF
TROPISM
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21. Chemotropism THERMOTROPISM HYDROTROPISM
(“Therm” – “heat”)
Thermotropism is the tendency of plants or other organisms to bend toward or away from heat.
Ex. curling of Rhododendron leaves in response to cold temperatures.
HYDROTROPISM
(“hydro” – “water”)
Hydrotropism is the growth in response to water. Ex. roots growing toward moisture
Chemotropism
(“Chemo” – chemical”)
Chemotropism is movement caused by chemical stimuli. Ex. Growth of a pollen tube is always towards the ovules
so that reproduction can occur
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