SBI3U: Plants: Anatomy, Growth, and Function
Student Activity: Plant Tropisms Part 1
Topics
plant
tropism
stimulus
Timing
preparation: 5 min
demonstration: 10 min
Specific Expectations SBI3U
Introduction
This student activity illustrates how plants grow away from/towards a stimulus by continuing
cell growth and elongation on one side of the stem while ceasing cell growth and elongation on
the opposite side of the stem. This connects to the curriculum by allowing students to be able to
explain how this change in growth happens.
Materials
Screen
Projector connected to show YouTube video
https://www.youtube.com/watch?v=3MYJEm99MYQ
Safety Considerations
If a student cannot complete the activity, they can watch the others.
Procedure
Preparation
Show the class this very short video showing the phototropism of young plants:
https://www.youtube.com/watch?v=FC5eBkDJbMs
Predict/Explain
Instruct students to find a partner and work in pairs.
Ask them to think about the video and think of how the plant grows toward the light.
Explanations need to be recorded so they can be reviewed later.
Observe
Ask students to stand up for this activity.
Instruct students to clasp hands together in front, keeping your elbows together below the wrists.
Keep wrists relaxed with fists pointing up.
Keeping right hand still and the wrists relaxed, push up with the left arm.
Ask student pairs to describe what they observe.
Bring hands back to starting position.
Keeping left hand still and the wrists relaxed, push up with right.
Ask student pairs to describe what they observe.
Explain
Review the original explanation for how plants move and revise this based on the activity.
Disposal
None
What happens?
Clasped hands will be bend into the direction opposite the hand pushing up.
How does it work?
Students’ clasped hands will be bent in a way that is very similar to how plants change the
direction of their growth. Plants can sense various stimuli such as light, gravity, chemicals,
water, and many others. Perception of these stimuli encourages the plant to grow toward or
away from the stimulus, depending on the nature of the stimulus.
In the case of light, plants tend to grow towards a source of light. Cells on the side of the stem
opposite the perceived light stimulus continue to grow, but cells on the side of the stem nearest
the perceived light stimulus stop growth. The result is the bending of the stem toward the
perceived light stimulus over a period of several hours/days.
Teaching Suggestions/Hints
Continue this lesson by outlining other tropisms in terms of environmental factors.
This is a good place for students to design an investigation to study tropisms with sprouting
seeds, seedlings or plants.
Next Steps
Link this demo to real plants more effectively by putting some wilted celery in water to sit
overnight to show students the role plays in helping plant cells be turgid again.
Keep some celery out of the water as a control.
This demo can be used together with Plant Tropisms Part 2.
Additional Resources
This demo was modified from: http://www.cals.ncsu.edu/nscort/outreach_exp_tropism.html
This video shows phototropism in young tomato plants:
http://www.youtube.com/watch?v=Ze8NV7cvW8k
Specific Expectations
SBI3U
A1.1 formulate relevant scientific questions about observed relationships, ideas, problems, or
issues, make informed predictions, and/or formulate educated hypotheses to focus inquiries
or research
F3.4 describe the various factors that affect plant growth (e.g., growth regulators, sunlight, water,
nutrients, acidity, tropism)