Trace auxin from the shoot tip to growing tissue
State its source and the syllabus movement account.
Extended only (Supplement); 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
Where is auxin made in this shoot account?
What you will learn
- Locate auxin production in the shoot tip
- Describe movement from the tip through plant tissue
Trace auxin from the shoot tip to growing tissue
| Feature | Meaning |
|---|---|
| Source | Shoot tip |
| Movement | Diffuses through the plant from the shoot tip |
| Redistribution | Different amounts on opposite sides |
| Effect | Stimulates shoot cell elongation |
Locate auxin production in the shoot tip
Auxin is made in the shoot tip. This identifies the source of the plant growth regulator in the Cambridge shoot-growth account. The shoot tip is not the root tip, the pancreas or a gland connected to an animal bloodstream. The growing region below the tip responds to the chemical signal, so the place where a signal is made need not be the same as every place where its effect is expressed.
The syllabus states that auxin diffuses through the plant from the shoot tip. Use that required movement account to connect the source with tissue below the tip. Diffusion is movement of particles associated with a concentration difference, not a muscle pulling a liquid or an electrical impulse jumping a synapse. The wording is a syllabus-level account; detailed transport biology involves additional processes beyond this lesson.
Describe movement from the tip through plant tissue
Movement from the tip and redistribution between sides are distinct ideas. Movement explains how the chemical reaches responsive growing tissue. Redistribution explains why one side of that tissue can receive a different amount under directional light or gravity. Keeping the two links separate prevents an answer that names the tip but leaves out the unequal distribution needed for curvature.
Auxin reaching a growing region stimulates shoot cell elongation in the required model. Equal amounts on both sides can support equal elongation without a lateral curve; an unequal distribution can cause differential elongation. Do not treat the presence of auxin alone as proof of a curve, or the absence of a curve as proof that there is no auxin or no growth. Later lessons apply the complete chain to each directional stimulus.
Pause and explain
Which pair separates movement and redistribution correctly?
Worked example
Give the source and syllabus movement account for auxin.
Show the worked solution
- Auxin is made in the shoot tip.
- It diffuses through the plant from that tip.
Answer Auxin is made in the shoot tip and diffuses through the plant from the shoot tip.
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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 where auxin is made and how the syllabus describes its movement.
Give me a hint
Use the specified source and movement wording.
Compare my reasoning
- It is made in the shoot tip.
- It diffuses through the plant from the shoot tip.
Auxin is made in the shoot tip and diffuses through the plant from the shoot tip.
Look for these in your work
- Name shoot tip
- Include diffusion from the tip
Distinguish auxin movement from unequal distribution.
Give me a hint
Think along the shoot versus between its sides.
Compare my reasoning
- Movement connects the tip with growing tissue below.
- Unequal distribution gives different amounts on opposite sides.
Movement carries the signal from the shoot tip through plant tissue; unequal distribution means different amounts on the two sides of a growing region.
Look for these in your work
- Explain source-to-tissue movement
- Explain the side-to-side difference
A shoot grows straight while its tip produces auxin. Why is that compatible with the model?
Give me a hint
Presence of auxin is not the same as unequal distribution.
Compare my reasoning
- Auxin can support cell elongation on both sides.
- Similar elongation on both sides permits straight growth.
Auxin can stimulate elongation on both sides. If the sides elongate similarly, the shoot can grow straight without a lateral curve.
Look for these in your work
- Allow growth with auxin
- Distinguish equal growth from curvature
Common mistakes
- Naming a root tip as the required shoot-source answer.
- Replacing plant tissue movement with blood transport.
What can you explain now?
Which pair separates movement and redistribution correctly?
Compare with the explanation
From tip to tissue; then unequal distribution between sides
These are different links in the growth explanation.
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Make it stick
State source and movement, then distinguish tissue transport from the unequal distribution that can cause bending.
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.