Test the carbon dioxide requirement with matched chambers
Separate a gas-removal treatment from its other possible effects.
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 does the design need a sealed chamber?
What you will learn
- Separate a gas-removal treatment from its other possible effects.
- Use the stated evidence to explain the method and its limits.
Design the paired treatment
Use suitable plants with checked initial starch depletion. In the teacher-controlled design, a sealed transparent chamber contains a carbon dioxide absorbent kept separate from the plant; a matched chamber provides a comparison without carbon dioxide removal. The plants receive comparable light, water, temperature and treatment time.
Teacher or technician handling is essential for the absorbent and sealed apparatus. For example, soda lime is corrosive and should not contact the plant or be handled as an unsupervised household experiment. A matched chamber and appropriately comparable inert material help separate carbon dioxide removal from the mere presence of a dish.
Connect the result with raw materials
After treatment, test comparable leaves for starch using the supervised preparation and working reagent controls. Starch detected in the carbon-dioxide-available comparison but not in the removal treatment supports the need for carbon dioxide in new carbohydrate synthesis.
Gas leakage, different chamber temperatures, residual starting starch or direct chemical damage weaken the inference. A dying plant exposed directly to absorbent is not a clean test of photosynthetic raw-material requirements. Written interpretation does not establish practical competence.
Sources for this lesson
Pause and explain
Which observation weakens a carbon-dioxide-only inference?
Worked example
Initially starch-negative plants in matched lit chambers differ only in a verified carbon dioxide removal treatment. The comparison tests positive for starch; the removal plant tests negative. Interpret.
Show the worked solution
- Identify carbon dioxide as a raw material.
- Use matched conditions and working tests.
- Relate the missing raw material to restricted new starch formation.
Answer The controlled result supports carbon dioxide being required for photosynthetic carbohydrate synthesis.
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.
Name the raw material being changed and the final leaf observation.
Give me a hint
Separate treatment and dependent observation.
Compare my reasoning
- Change carbon dioxide availability.
- Observe starch detection with iodine.
Carbon dioxide availability is changed; starch detection is observed after treatment.
Look for these in your work
- State both roles.
- Do not call oxygen the removed raw material.
The removal chamber leaks, and both plants form starch. Does this establish that carbon dioxide is unnecessary?
Give me a hint
Check whether the intended gas treatment was achieved.
Compare my reasoning
- Leaked air can supply carbon dioxide.
- The treatment has not excluded the raw material.
- Repair and verify the chamber before interpreting.
No; gas leakage invalidates the intended carbon dioxide removal comparison.
Look for these in your work
- Identify leakage.
- Avoid a false requirement conclusion.
The removal plant becomes scorched because the chamber also heats much more. Suggest a correction and explain why it matters.
Give me a hint
Temperature changed along with the gas treatment.
Compare my reasoning
- Match and measure chamber temperatures.
- Keep light and other conditions comparable.
- Separate heat damage from missing carbon dioxide.
Control temperature and prevent damage so the comparison can isolate carbon dioxide availability.
Look for these in your work
- Name the confounder.
- Specify a matched redesign.
Common mistakes
- Use a matched chamber, not an uncovered plant in a different environment.
- Keep hazardous absorbent separate and teacher-controlled.
What can you explain now?
Which observation weakens a carbon-dioxide-only inference?
Compare with the explanation
The absorbent directly damages the plant.
Chemical damage is another possible cause.
After trying it yourself, choose your next review. This is your self-assessment.
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Make it stick
Explain the purpose of the comparison chamber and one treatment-failure check.
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.