Living Creatures: Exploring their Characteristics · Lesson 4 of 8
How Roots and Shoots Grow
“Observe how upright, inverted and side-lit seedlings reveal directional growth.”
• Set out the three seedling arrangements and identify what each comparison tests. • Predict and explain how roots and shoots grow after a seedling is inverted. • Explain the shoot’s response when light comes from only one side. • Distinguish plant growth movement from a whole plant travelling. • Relate careful measurements of plant response to Jagadish Chandra Bose’s work.
A rooted plant can still change direction
After a seed sprouts, its root and shoot do not always continue in the direction they pointed when first seen. A root can bend down and a shoot can bend up. Growth makes this slow movement visible over days. We can test direction by changing a seedling’s starting position or the direction from which light reaches it, while keeping the seedlings moist.
Start with bean or gram seedlings grown on moist cloth until each has a small root and shoot. Carefully attach one to each of three upright glass plates covered with wet blotting paper; place the plates in beakers so the seedlings remain above the water but receive moisture from the paper. Avoid damaging delicate parts when attaching them. These shared conditions make the differences among A, B and C more informative.
Three arrangements answer two questions
In A, the seedling is upright with light reaching it broadly. In B, turn the seedling upside down but keep the light conditions similar to A. In C, keep the seedling upright but place it inside a box with a hole that admits light from one direction. Record a prediction for the root and shoot separately, then observe how each grows over time. A and B test the starting orientation; A and C test the light direction.
| Setup | Starting position and light | Shoot observed | Root observed |
|---|---|---|---|
| A | Upright; light broadly available | Upward | Downward |
| B | Inverted; light broadly available | Bends and grows upward | Bends and grows downward |
| C | Upright; light from one side | Bends toward the light | Continues downward |
Problem
A seedling initially has its shoot pointing downward and its root upward. What should be observed after suitable growth conditions continue?
- 1.Recognise that these directions are the initial positions caused by inversion, not the final directions of new growth.
- 2.The root bends and new growth heads downward.
- 3.The shoot bends and new growth heads upward. Both parts can move through growth even while attached to the seedling.
Use light as a directional clue
When only one side of a box admits light, the shoot can bend toward that opening. The root continues its downward growth. These observations combine two ideas from earlier lessons: plants grow, and they respond to their surroundings. The three arrangements do not show a whole plant walking toward light; they show parts gradually changing their direction as they grow.
Problem
A student sees a shoot bend toward a hole in a box. Which setup would help test whether one-sided light matters?
- 1.Use C, the upright seedling receiving light through a hole, as the observed case.
- 2.Compare with A, another upright seedling given broader light while moisture is maintained.
- 3.A different direction of shoot growth in C supports the connection with directional light; record roots too, since they do not follow the shoot toward the hole.
Jagadish Chandra Bose studied how plants respond to changes such as light, heat, electricity and gravity. He developed the crescograph to measure tiny changes in plant growth. His work is relevant because the seedling bends too slowly for a brief glance to tell the story; careful observations and measurements reveal the response.
An inverted seedling does not flip itself back like a toy. Newly growing parts bend over time, so record the original position and subsequent changes.
Quiz
In the chapter’s arrangement, what is the main difference between A and B?
After an inverted seedling has grown, its root generally:
What happens to the shoot when an upright seedling receives light from only one side?
Why is the blotting paper kept moist?
Which conclusion best fits all three setups?
What did the crescograph help Bose measure?
Practice Problems
- Sketch A, B and C before and after several days. Label the root and shoot directions in each.
- Explain why A versus B is a useful comparison and what A versus C investigates.
- A pot is placed on its side. Predict the directions of new root and shoot growth and explain how this differs from simply rotating a finished drawing.
- Describe how to keep seedlings moist without submerging them in the three-beaker setup.
- Explain the difference between a shoot bending toward light and a plant travelling to another location.
- What might a student miss by observing only once at the beginning and once after a few minutes? Design an observation schedule.
Key Takeaways
• Roots generally grow downward, including after a seedling is inverted. • Shoots generally grow upward and can bend toward light from one side. • Compare arrangements that differ in orientation or lighting while keeping moisture suitable. • Growth can make plant movement visible over time. • Careful observations and instruments reveal responses that are too slow to notice in a moment.