Final Answer:
Tropism is a plant’s growth response to an environmental stimulus. They can be positive (growth toward the stimulus) or negative (growth away from the stimulus).
- Positive Tropism: e.g., a stem growing toward light (phototropism).
- Negative Tropism: e.g., roots growing away from light.
Remember a stimulus is a change in the environment that causes a response.
Seasonal Responses: plants living in regions that get cold can detect changes in the season and adapt to them. Example: deciduous trees drop leaves in fall to conserve water and energy.
Short-day plants: plants that grow better when the night is longer than the day (example: poinsettia, chrysanthemum).
Long-day plants: plants that grow better when the night is shorter than the day (example: spinach, lettuce).
Can humans manipulate plants to grow differently? Yes — if so, how? By controlling light exposure (e.g., using grow lights or black cloths to simulate long/short nights), temperature, or hormones (like auxins).
Phototropism
“Photo” means light
Definition: growth of a plant toward or away from light.
Gravitropism
“Gravi” means gravity
Definition: growth of a plant in response to gravity (roots = positive gravitropism; stems = negative gravitropism).
Thigmotropism
“Thigmo” stands for touch
Definition: growth response to physical contact (e.g., vines coiling around a trellis).
Hydrotropism
“Hydro” means water
Definition: growth of roots toward water sources.
Movie Table:
1. “Sunflower Phototropism”
Tropism: Phototropism
Stimulus: Light (sun)
Plant Response: Stem bends to face the sun
Illustration: Sunflower turning toward sunlight
2. “Sensitive Plant”
Tropism: Thigmotropism (actually, it's a *nastic* movement—see Q4—but worksheet says thigmotropism, so follow instructions)
Stimulus: Touch
Plant Response: Leaves fold inward quickly
Illustration: Leaflets closing when touched
3. “Corn root gravitropism”
Tropism: Gravitropism
Stimulus: Gravity
Plant Response: Roots grow downward
Illustration: Corn roots growing straight down into soil
4. What is the nastic?
A nastic movement is a rapid, reversible plant response to a stimulus that does *not* depend on the direction of the stimulus (unlike tropisms).
One type of nastic:
Thigmonasty (e.g., mimosa leaves folding when touched).
Photo: (student would draw or paste image of mimosa leaf closing)
Note: For #2, technically the sensitive plant shows *thigmonasty*, not thigmotropism—but since the worksheet labels it thigmotropism, fill as instructed.
Parent Tip: Review the logic above to help your child master the concept of tropism worksheet.
