1. Tropisms and Turgor Pressure Notes: Stimulus and Response in Plants
Stimulus = Light
Stimulus = Touch

2. INternal Stimuli in Plants
Turgor Pressure
The outward pressure that occurs in a plant cell when the cytoplasm and vacuoles fill up with water and the cell membrane pushes against the cell wall.
Presence of water  turgid cell aka healthy plant cell
Absence of water  flaccid (limp) cell aka dying plant cell
KEY
Stimulus
Response
Draw this picture and label each as turgid or flaccid.

3. Turgor Pressure Animation
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Turgor Pressure Animation
Click on the picture or hyperlink to watch an animation that shows a plant cell gain and lose Turgor Pressure. Watch it for about 2 minutes in order to see the effect of a full vacuole and a low-pressure vacuole.
The PPT must be in Slide Show Mode to access the link.
Click HERE to view the animation

4. EXternal Stimuli in Plants
Tropisms
Tropisms: a plant’s growth in response to an external stimulus.
Positive (+) tropism: Plant growth toward a stimulus (water, sunlight)
Negative (-) tropism: Plant growth away from a stimulus (spilled gas, toxins, too much sun or not enough)

5. Emergence of Seedlings (plants coming out of their seed)
Seeds are actually immature plants (seedlings) with a thick, hard coat covering them.
The seed coat (outside of a seed) protects the beginning of a root, the beginning of a stem, either one or two seed leaves, and the seed’s food supply.
The seedling’s stem and roots exert a strong force that enable it to break free of the coat or hard shell when conditions are right.
Factors necessary for most seed emergence:
Warm/moist soil
Longer days of sunlight (spring)
VIDEO:
Click HERE to observe seedling emerging
Stem
Broken
seed coat
Roots
Pecan sprouting

6. Phototropism Growth of a plant in response to light.
The stalk displays positive phototropism growing towards the light.
The roots display negative phototropism growing away from the light.

7. Geotropism (Gravitropism)
Earth
Growth
Gravity
Growth
Growth of a plant in response to earth / gravity.
The roots display a positive geotropism growing towards earth (with gravity.)
The stalk displays a negative geotropism growing away from gravity.
Negative
Positive

8. Seed placement (orientation)
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It does not matter which way you plant a seed in the ground.
The root cells will always grow down towards earth because of their response to gravity (geotropism).
The stem cells will always grow towards light (phototropism).
Root
Top of seed

9. Hydrotropism Growth of a plant in response to water.
The roots display a positive hydrotropism growing towards water.
The stalk display a negative hydrotropism growing away from water.
Positive
Water

10. Thigmotropism Moves or grows in response to touch or contact stimuli.
Growth
Moves or grows in response to touch or contact stimuli.
A vine displays a positive thigmotropism growing towards touch
Vine growing against a wall
Venus Fly Trap closing when touched
The leaves display negative thigmotropism growing away from touch

11. The PPT must be in Slide Show Mode to access the link.
Read Only
View the video below to hear a teacher who created a song about tropisms.
Click HERE for the Tropisms Song
The PPT must be in Slide Show Mode to access the link.

12. Tropisms Notes Assignment
Phototropism
Geotropism
Draw a picture of each tropism showing its positive response to each stimulus listed.
Label what is happening in each picture.
Hydrotropism
Thigmotropism
Color is optional.