Interpret evidence from a stained shoot
Evaluate tissue localisation, external contamination and the limits of a tracer result.
Mapped to the named 0654 section using teaching from the corresponding single-science course. A 0654-specific review of every Core and Supplement objective is still in progress. Written practice is self-checked; it does not demonstrate supervised laboratory competence or award an official Cambridge grade.
Before you begin
- Complete the supervised stain-method lesson.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
Why use a tissue key?
What you will learn
- Interpret section observations against a tissue key
- Separate evidence, inference and limitations
Locate the stain before concluding
In supplied observations, the treated shoot has coloured inner vessel regions matching the xylem key, while the water-only comparison lacks the introduced colour. This pattern supports movement of the stained solution along xylem in the shoot.
A leaf becoming coloured alone is less precise evidence. Identify whether stain lies in veins and their xylem region rather than assuming all visible leaf colour names a conducting tissue. The external cut surface can become stained without revealing the route above it.
Avoid a stronger claim than the method supports
A tracer can locate a pathway, but an uncalibrated coloured distance is not automatically a volume-flow rate. Different tissues bind stain differently, and colour intensity also depends on concentration and preparation.
An unexpected coloured phloem region needs investigation: section contamination, staining technique, time and tracer behaviour could matter. Repeat with controls and better localisation before overturning the tissue pathway on a single ambiguous view. Written interpretation remains separate from practical performance.
Sources for this lesson
Pause and explain
What is the strongest supported conclusion from the supplied internal xylem result?
Worked example
The shoot exterior is coloured, but no internal section is recorded. Can xylem transport be concluded?
Show the worked solution
- External colour could be a splash.
- Internal localisation against a tissue key is missing.
Answer No. Exterior colour alone does not establish the internal tissue pathway.
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.
Treated xylem is coloured; matched control xylem lacks that colour. State a supported conclusion.
Give me a hint
Use treatment and tissue localisation together.
Compare my reasoning
- The introduced colour differs from the control.
- Its location matches xylem.
The stained solution travelled along xylem in the treated shoot under the stated conditions.
Look for these in your work
- Use control evidence
- Identify the tissue pathway
Two sections differ in colour intensity. Why is “twice as dark means twice the water-flow rate” unsupported?
Give me a hint
Name another cause of intensity and the missing measurement.
Compare my reasoning
- Intensity depends on stain concentration, binding and section preparation.
- Flow rate needs calibrated amount per time.
Colour intensity alone is not a calibrated water-volume/time measure, so it does not prove a twofold flow rate.
Look for these in your work
- Give an intensity limitation
- State the rate measurement needed
Stain is also seen on an exterior leaf surface after splashing. How could the evidence be improved?
Give me a hint
Separate contamination from an internal route.
Compare my reasoning
- Prevent splashes and retain a matched unstained control.
- Examine clean internal vein sections against the key, with repeated preparations.
Repeat with contamination controlled and localise stain inside identified xylem rather than relying on surface colour.
Look for these in your work
- Control contamination
- Require internal tissue evidence
Common mistakes
- Treating colour intensity as an exact flow rate.
- Discarding controls when a result appears visually convincing.
What can you explain now?
What is the strongest supported conclusion from the supplied internal xylem result?
Compare with the explanation
The stained solution followed shoot xylem
The localisation supports this pathway in the setup.
After trying it yourself, choose your next review. This is your self-assessment.
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Make it stick
State one valid tracer conclusion and two conclusions it cannot establish by itself.
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.