Compare gravitropism in roots and shoots
Describe the contrasting directions after a horizontal start.
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 part usually shows positive gravitropism?
What you will learn
- Describe the usual root and shoot responses
- Use a fixed gravity reference for both parts
Compare gravitropism in roots and shoots
| Feature | Meaning |
|---|---|
| Root | Usually positive gravitropism |
| Shoot | Usually negative gravitropism |
| Darkness | Excludes directional light; gravity still acts |
| Evidence | Compare initial and later growth with the container fixed |
Describe the usual root and shoot responses
In a typical germinating seedling, the root shows positive gravitropism and the shoot shows negative gravitropism. The root grows towards gravity and the shoot grows away from it. A seed lying sideways can therefore produce a root curving downwards and a shoot curving upwards. The opposite directions belong to different growing parts, not to gravity reversing direction.
Use the same gravity arrow when comparing the two parts. An upright photograph may show a straight root pointing down and a straight shoot pointing up; the directions are consistent with the usual responses, but a timed horizontal-start investigation provides stronger evidence of a change in growth direction. Label root and shoot rather than identifying them only from their eventual position.
Use a fixed gravity reference for both parts
A suitable comparison keeps seedlings moist and at a suitable temperature, fixes the container after the initial rotation and excludes directional light. Darkness removes light as a competing directional stimulus; it does not remove gravity. Record a starting outline and later growing-tip directions. Repeat with several similar seedlings so one damaged or atypical specimen does not determine the whole conclusion.
The root and shoot curves should be described separately. A shoot curving upwards in darkness is not evidence of phototropism, because no one-sided light stimulus is provided. A root growing down is not described as negative simply because it is below the seed. The sign refers to growth towards or away from the named stimulus, and these examples use gravity.
Pause and explain
Why keep a gravity comparison in darkness?
Worked example
Describe both parts of a horizontal seedling kept in darkness.
Show the worked solution
- The root curves towards gravity.
- The shoot curves away from gravity.
Answer Root: positive gravitropism, downwards. Shoot: negative gravitropism, upwards.
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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.
State the usual gravitropic response of a root and a shoot.
Give me a hint
Use one gravity reference for both.
Compare my reasoning
- Root grows towards gravity.
- Shoot grows away from gravity.
Root: positive gravitropism. Shoot: negative gravitropism.
Look for these in your work
- Name both plant parts
- Give both response signs
A horizontal seedling has a root curving down and a shoot curving up in darkness. Describe the two growth directions.
Give me a hint
Direction is relative to gravity, not the seed.
Compare my reasoning
- The root curve is towards gravity.
- The shoot curve is away from gravity.
The root grows down towards gravity; the shoot grows up away from gravity.
Look for these in your work
- Describe both curves
- Retain the common gravity reference
Correct: the shoot grew upwards in darkness because it followed the light above the seed.
Give me a hint
No directional light was supplied.
Compare my reasoning
- Darkness removes the proposed light cue.
- Upward shoot growth is away from gravity.
The upward shoot response in this dark setup is negative gravitropism, not evidence of following a light source.
Look for these in your work
- Use the stated experimental condition
- Identify the appropriate stimulus
Common mistakes
- Calling every downward response negative.
- Attributing an upward curve in darkness to a lamp.
What can you explain now?
Why keep a gravity comparison in darkness?
Compare with the explanation
To exclude directional light as a competing stimulus
Gravity still acts in darkness.
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Make it stick
Describe the contrasting root and shoot growth directions in a dark horizontal-start investigation.
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.