Investigate gravitropism in seedling shoots
Test an upward growth response while excluding directional light.
Section 14.5 · Tropic responses
Exam scope and assessment notes
Core and Extended · Biology 0970, 2026–2028. Use the stated specimen features and evidence. Diagrams are schematic. Written practice is self-checked; human subject-teacher review, supervised practical competence and cumulative assessment remain pending. Cambridge states that IGCSE 0970 has the same subject content as IGCSE 0610, with 9–1 grading. This StudyForA pathway maps the 2026–2028 syllabus only. This 9–1 graded qualification is available only in a limited number of administrative zones. Confirm that your centre can enter you for this code and exam series with Cambridge International. Cambridge has published a separate syllabus for 2029. StudyForA has not reconciled that version yet; this page supports exams in 2026, 2027 and 2028 only.
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
Why use darkness for both shoot groups?
What you will learn
- Create a horizontal shoot start in darkness
- Describe and measure the later growth direction
Investigate gravitropism in seedling shoots
| Feature | Meaning |
|---|---|
| Change | Starting shoot orientation relative to gravity |
| Measure | Timed tip curvature and growth direction |
| Expected response | Horizontal shoots curve up, away from gravity |
| Controls | Darkness, moisture, temperature, age and observation interval |
Create a horizontal shoot start in darkness
Use similar young seedlings with actively growing shoots, supported so their stems are not crushed or bent by the holder. Under teacher guidance, set one group with shoots approximately horizontal and keep a matched group upright. Draw or photograph the initial axes. Fix the supports after this change so any later curvature is not produced by repeatedly turning the container.
Keep both groups in darkness for the same suitable interval to exclude one-sided light as an alternative directional cue. Keep species, age, initial shoot size, moisture and temperature comparable. The independent variable is starting shoot orientation relative to gravity. The dependent variable can be the change in growing-tip angle from its own starting axis, with the direction recorded separately.
Describe and measure the later growth direction
The usual prediction is that the horizontal shoots develop growth curving upwards, away from gravity, while an upright comparison needs little corrective curvature. Repeat the measurements with several seedlings and use the same photographic perspective. A marked starting outline makes it easier to judge new curvature without confusing a pre-existing bend with the later response.
A shoot that merely droops under its own weight is not sufficient evidence of negative gravitropism. Look for developing growth in the region near the tip over time. A rotating clinostat can be used in an extension comparison under teacher supervision, but it changes the plant’s orientation continually rather than turning gravity off. Written planning and supplied data remain separate from supervised practical competence.
Pause and explain
What does a rotating clinostat do in this comparison?
Worked example
A horizontal shoot curves up in a fixed dark setup. Describe the response.
Show the worked solution
- Upwards is away from gravity.
- The new growth is a negative gravitropic response.
Answer The shoot shows negative gravitropism.
Try a topic test
Choose Easy, Normal or Difficult. Save your answers and open worked review after finishing.
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 a changed factor and a measured response for the shoot-gravity investigation.
Give me a hint
Use orientation and later growth, not lamp colour.
Compare my reasoning
- Vary starting shoot orientation relative to gravity.
- Measure tip curvature and record its direction after a fixed interval.
Changed factor: starting shoot orientation relative to gravity. Measured response: later shoot-tip curvature and direction.
Look for these in your work
- Identify orientation
- Measure timed growth
Describe the predicted contrast between horizontal and upright shoots in darkness.
Give me a hint
Each angle is compared with its own starting axis.
Compare my reasoning
- Horizontal shoots curve up away from gravity.
- Upright shoots need little corrective curvature.
Horizontal shoots develop upward growth, showing negative gravitropism; upright comparison shoots are predicted to show little corrective curvature.
Look for these in your work
- Describe both groups
- Relate growth to gravity
A method uses horizontal shoots beside a lamp and upright shoots in darkness. Why does it not isolate the effect of starting orientation?
Give me a hint
Two directional conditions change together.
Compare my reasoning
- Orientation and illumination both differ.
- Keep light conditions the same while varying orientation.
The method changes both orientation and light conditions, so the result is confounded. Use the same dark conditions for both orientation groups.
Look for these in your work
- Identify both changed conditions
- Give a controlled repair
Common mistakes
- Using a side lamp during a gravity-only comparison.
- Saying a clinostat removes gravity.
What can you explain now?
What does a rotating clinostat do in this comparison?
Compare with the explanation
Continually changes the plant’s orientation relative to gravity
It does not switch gravity off.
After trying it yourself, choose your next review. This is your self-assessment.
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Make it stick
Plan the shoot comparison and explain why darkness or a clinostat does not remove gravity.
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.