Use variegated-leaf evidence for the chlorophyll requirement
Match the original pigment pattern to subsequent starch detection.
Section B6.1 · Photosynthesis
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
- Recall chloroplasts, enzymes and the difference between photosynthesis and respiration.
- Use the stated observations, quantities and controls; diagrams are schematic.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
Why record the original green and white pattern?
What you will learn
- Match the original pigment pattern to subsequent starch detection.
- Use the stated evidence to explain the method and its limits.
Record the pattern before removing pigment
A variegated leaf has green and non-green areas. On a suitable initially destarched plant, trace or photograph the original pattern before light exposure and the later supervised decolourisation. That record is essential because the pigment pattern is removed during starch-test preparation.
Compare the starch-positive pattern with the original green areas. In the supplied standard model, green regions have chlorophyll and non-green regions lack it. Keep light, water and carbon dioxide available to both regions and verify working test controls.
Limit the conclusion to the evidence
Starch detection in originally green regions and no detection in originally non-green regions supports the chlorophyll requirement under the controlled conditions. The explanation links pigment to light-energy transfer, not the claim that green dye is itself carbohydrate.
Variegated tissues can differ in other ways, and carbohydrate can move between regions. Repeated suitable leaves and careful initial checks strengthen the interpretation. Do not treat a final leaf photograph without a recorded original pattern as sufficient evidence for which region contained chlorophyll.
Sources for this lesson
Pause and explain
Which connection explains the expected green-region result?
Worked example
The recorded green patches of a destarched variegated leaf later test blue-black. Recorded white patches remain yellow-brown. What requirement is supported?
Show the worked solution
- Locate the original chlorophyll-containing regions.
- Match them to starch detection.
- Connect chlorophyll with light-energy transfer.
Answer The result supports chlorophyll being required for photosynthetic starch formation in this controlled leaf comparison.
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.
State the two patterns that must be compared in this investigation.
Give me a hint
One is recorded before preparation.
Compare my reasoning
- Record green and non-green areas.
- Compare starch-positive and negative areas after iodine.
The original pigment pattern and the subsequent starch-detection pattern.
Look for these in your work
- Include both observations.
- Keep their timing clear.
A prepared decolourised leaf is blue-black in one patch, but its original pigment pattern was not recorded. Can that patch alone establish the chlorophyll requirement?
Give me a hint
The region’s prior pigment status is missing.
Compare my reasoning
- A starch-positive patch is known.
- Whether it originally contained chlorophyll is unknown.
- The required association cannot be checked.
No; the original chlorophyll pattern is needed to associate pigment presence with starch formation.
Look for these in your work
- Name the missing record.
- Limit the inference.
A white region also shows a small starch-positive patch. Give two checks before declaring chlorophyll unnecessary.
Give me a hint
Consider initial stores, pigment mapping and movement.
Compare my reasoning
- Verify initial starch depletion and exact pigment boundaries.
- Check reagent controls and possible carbohydrate movement.
- Repeat comparable leaves under matched conditions.
Check prior starch and pigment mapping, then working controls and possible transport before interpreting the unexpected result.
Look for these in your work
- Give plausible checks.
- Do not ignore the unexpected observation.
Common mistakes
- Record the pattern before removing pigment.
- Chlorophyll is not the starch product.
What can you explain now?
Which connection explains the expected green-region result?
Compare with the explanation
Chlorophyll supports light-energy transfer into carbohydrate chemicals.
That links pigment presence to synthesis.
After trying it yourself, choose your next review. This is your self-assessment.
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Make it stick
Describe the controlled association and one reason a pattern mismatch needs checking.
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.