Investigate phototropism in visible seedling roots
Measure a stated root-light response while accounting for gravity.
Core and Extended; Biology 0610, 2026–2028. Use the stated specimen features and evidence. Diagrams are schematic. Written practice is self-checked
Before you begin
- Identify the root and shoot of a seedling; recall growth, cell structure and the variables in a controlled investigation.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
Which root must be observable for this method?
What you will learn
- Provide controlled lateral light to visible roots
- Compare lateral curvature with a matched control
Investigate phototropism in visible seedling roots
| Feature | Meaning |
|---|---|
| Change | One-sided versus even blue illumination |
| Measure | Lateral root curvature relative to the starting vertical axis |
| Controls | Gravity orientation, uniform moisture, temperature, age and time |
| Limit | Root response may be weak; do not invent a universal sign |
Provide controlled lateral light to visible roots
A root-light investigation must expose visible growing roots to a known directional source; roots hidden in opaque soil cannot supply a clear direct curvature record. Published Arabidopsis investigations use visible roots on vertical transparent growth plates and controlled one-sided blue light. A classroom adaptation requires teacher-selected seedlings and suitable conditions that give a measurable root response, rather than a promise that any seedling will curve strongly.
Keep the root axes initially vertical and compare one-sided blue illumination with an evenly illuminated blue-light control. Record the source side. Maintain the same downward gravity orientation in both groups, even moisture without a lateral water gradient, suitable temperature, species, age and observation time. Match illumination as closely as possible and report any intensity difference. Gravity continues to act and can outweigh a weak lateral light response.
Compare lateral curvature with a matched control
Use timed photographs from the same perspective to measure lateral growing-tip curvature relative to the original vertical axis. Record its direction towards or away from the source as well as angle magnitude. Repeat with several seedlings and compare means and spread with the control. In the stated negative-response model, roots curve laterally away from blue light while continuing to grow downwards.
A clear difference supports a response under the stated conditions; it does not establish that every root avoids every wavelength. If no clear difference appears, report it and evaluate exposure, gravity dominance and measurement uncertainty rather than inventing a result. Handle growth materials under teacher guidance, wash hands and separate moisture from electrical equipment. Written planning does not replace supervised practical work.
Pause and explain
Which inference is justified by repeated curvature away from blue light in the stated setup?
Worked example
In the stated model, roots grow down and curve right with blue light from the left. Describe the response.
Show the worked solution
- The lateral curve is away from the source.
- Downward growth remains towards gravity.
Answer Negative phototropism in the stated model, alongside positive gravitropism.
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Test this topic →From guided practice to a new situation
Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
Identify the changed factor and the measured response in this visible-root light comparison.
Give me a hint
Separate illumination treatment from lateral growth.
Compare my reasoning
- Vary one-sided versus evenly distributed blue illumination.
- Measure lateral root-tip curvature and its source-relative direction.
Changed factor: direction of blue illumination. Measured response: lateral root-tip curvature and direction after a fixed interval.
Look for these in your work
- Name illumination direction
- Name a measurable root response
Why keep gravity orientation and moisture distribution the same between root-light groups?
Give me a hint
Roots respond to more than one directional influence.
Compare my reasoning
- Gravity can produce downward growth.
- A moisture gradient can create a competing influence.
Keeping gravity orientation and moisture distribution the same reduces competing directional influences, making the light comparison clearer.
Look for these in your work
- Account for gravity
- Avoid a moisture-gradient confound
Repeated roots show weak sideways curvature with overlapping treated and control readings. Evaluate the claim of a strong universal negative response.
Give me a hint
Use spread and the scope of the sample.
Compare my reasoning
- Overlapping readings do not clearly support a strong difference.
- One setup cannot establish a universal response.
The records do not clearly establish a strong treatment difference, and cannot support a universal claim. Report the weak or uncertain response and improve exposure control, repeats and angle measurement.
Look for these in your work
- Evaluate the spread
- Limit the conclusion and improve the method
Common mistakes
- Ignoring the continuing gravity stimulus.
- Allowing a water gradient to differ between light groups.
What can you explain now?
Which inference is justified by repeated curvature away from blue light in the stated setup?
Compare with the explanation
A negative root-light response under those conditions
It preserves the conditions and observed sign.
After trying it yourself, choose your next review. This is your self-assessment.
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Make it stick
Plan an observable root-light investigation and evaluate weak data without ignoring gravity or moisture.
If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.