Notes of different types of plant tropisms & stimuli

1. Plant Tropisms
The movement or growth of
a plant in response to a
stimulus…

2. What is a stimulus?
Stimulus: any change in an organism’s
environment that causes the
organism to react. It is a fancy way of
saying “cause”.
Stimulus – singular
Stimuli – plural
Example: An animal is cold so it moves into the sun.

3. What is a response?
Response: how the organism
reacts to a stimulus and results
in a change in behavior. It is a
fancy way of saying “effect”.
Example: Getting a drink when you are
thirsty.

4. Plant Responses (Tropisms)
 Tropism is growth in response to an
external stimulus (Stimulus is a factor
that elicits a response).
 Positive tropism: Plant growth toward
a stimulus (Ex. water, sunlight)
 Negative tropism: Plant growth away
from a stimulus (Ex. spilled gas, toxins,
too much sun or not enough)

5. So, plants can move to respond to the
environment.
The stimuli for growth may be:
Light Touch
Water
Gravity

6. Some of these ways are:
 Phototropism
 Geotropism
 Hydrotropism
 Thigmotropism

7. Phototropism
 Phototropism is a
change in the growth
of a plant in response
to light.
 The stalk displays
positive phototropism
growing towards the
light.

8. Why?
Maximize amount of sun for
photosynthesis to make their food.

9. Positive
Phototropism
Plant
Illustrate phototropism on your paper.
Label your illustration as you would any scientific drawing.
(See rules on your paper!)
This stalk displays
positive
phototropism
growing towards
the light.

10. Time Lapse of Plants
Following Light
Click the link to watch:
https://www.youtube.com/watch?v=wjZ1UYwrO8A
READ ONLY

11. Corn
Dance
After 3 days of growth in darkness, the pot of corn seedlings in this movie
were exposed to light from a single light bulb placed in the center of the pot
just above the seedling. The plants were then imaged at 10 min intervals for
about 18 hours. For the first 14 hours the seedlings appear to be dancing to
the light as they maintain phototropic curvature. Since geotropism is
simultaneously affecting the seedlings, the curvature that develops is a
compromise between the opposing light and gravity responses. After 14
hours, the point light source was turned off and diffuse room lighting was
turned on, at which point geotropism becomes the dominant stimulus and the
seedlings quickly return to a vertical orientation. Frame playback is at 12
frames per sec.
Click the link to watch:
https://www.youtube.com/watch?
v=RZDwoteRuqA
READ ONLY

12. Geotropism
(Gravitropism)
 Geotropism is a change
in the growth of a plant
in response to gravity.
 The stalk displays a
negative geotropism
growing away from
gravity.
 The roots display a
positive geotropism
growing towards gravity.
Negative
Positive

13. Positive
Geotropism
Illustrate geototropism on your paper.
Label your illustration as you would any scientific drawing.
(See rules on your paper!)
The roots display
POSITIVE
phototropism
growing towards
gravity.

14. Gravitropism
Click the link to watch:
http://www.youtube.com/watch?v=8SkKuwbmR5Y
&feature=related&safety_mode=true&persist_safet
y_mode=1
Why?
Allows plants to grow properly
and get nutrients and sunlight

15. Geotropism
(Gravitropism)
Click the link to watch:
https://www.youtube.com/watch?v=mYZXax8V_L0
READ ONLY

16. Phototropism and
Geotropism Time Lapse
Montage
Click the link to watch:
https://www.youtube.com/watch?v=F3Oj2er-91s
READ ONLY

17. Hydrotropism
 Hydrotropism is a
change in the growth
of a plant in response
to water.
 The roots display a
positive hydrotropism
growing towards
water.
Positive
Water

18. Thigmotropism
 Thigmotropism is a movement in which an
organism moves or grows in response to
touch or contact stimuli.
 Thigmotropism
usually occurs when
plants grow around a
surface, such as a wall,
pot, or trellis.
Click the link to watch:
https://www.youtube.com/watch?v=m2xKjA69jNM

19. NASTIC RESPONSES are fast, reversible
movements and are non-directional. The
movement can be caused by changes in
turgor pressure or changes in growth.
Click the link to watch:
http://www.youtube.com/watch?v=O7eQKSf0LmY
Hungry Venus flytraps snap shut on a
host of unfortunate flies. But, despite its
name, flies aren’t the flytrap's only meal.
As long as its prey is roughly the right
size and touches two of its hairs within
twenty seconds, the plant will dine on
any insect or spider that comes its way.
Glands in the lobes then secrete
enzymes that break the dinner down
into a digestible soup. Ten days later,
the trap pops open to reveal nothing but
a dried out husk.
Venus Flytraps: Jaws of Death - BBC One
READ ONLY

20. Mimosa Pudica –
The Sensitive plant
https://www.youtube.com/watch?v=BLTcVNyOhUc
READ ONLY

21. External Stimulus
External stimulus: a stimulus that
comes from the external
environment (outside an organism)
Examples:
1. You feel cold so you put on a jacket.
2. A snake lunges at a rabbit so it runs away.
3. A dog feels hot so it goes to lay in the shade.

22. Internal Stimulus
Internal stimulus: a stimulus that
comes from inside an organism.
Examples:
1. You feel hungry so you eat some food.
2. A cat feels thirsty so it drinks water.
3. A dog feels hot so it goes to lay in the shade.

23. Make a T-chart on back of this paper and
label the columns internal and external.
Put the letter of each stimulus in the
proper column.
A. You have a stomach ache and decide
to lay down.
B. A bird is thirsty and drinks some water.
C. A squirrel sees a cat and runs up a tree.
D. A lion gets hungry and eats a gazelle.
E. You see a spider and scream.