Investigate temperature and photosynthetic gas release
Describe a tested temperature response with matched light and carbon dioxide.
Exam scope and assessment notes
Mapped to the named 0973 section using teaching from the corresponding single-science course. A 0973-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. This qualification reports two grades on the 9–1 scale; confirm the entry route for your zone and exam series.
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
Which measured temperature has the greatest supplied rate?
What you will learn
- Describe a tested temperature response with matched light and carbon dioxide.
- Use the stated evidence to explain the method and its limits.
Keep collection conditions controlled
Compare an aquatic plant at measured water temperatures using teacher-approved controlled baths. Match light, carbon dioxide treatment, plant quantity, adjustment time and gas collection duration. Check the actual water temperature rather than assuming a bath label is exact.
Use repeats and comparable fresh material if earlier heat exposure could cause lasting damage. Changes in water temperature can also affect gas solubility and collection, so gas-release measurements need careful interpretation.
Read the tested response
In the supplied example, gas-release rates at 10, 20, 30 and 40 °C are 0.2, 0.4, 0.6 and 0.1 cm³/min. The fastest tested setting is 30 °C, followed by a decline. Temperatures between those points have not been measured.
Photosynthesis involves enzyme-controlled reactions. A moderate rise can support faster reaction rates; excessive heat can disrupt enzyme function and damage tissues. These links help interpretation, but a decline in collection alone does not demonstrate that every enzyme has been denatured or establish a universal optimum for all plants.
Sources for this lesson
Pause and explain
Why could reusing a previously overheated plant weaken a later low-temperature comparison?
Worked example
Use the supplied 10–40 °C rates to state the response and fastest tested setting.
Show the worked solution
- Rates rise from 0.2 to 0.6 cm³/min between 10 and 30 °C.
- They fall to 0.1 cm³/min at 40 °C.
- 30 °C is fastest tested, not a precisely established universal optimum.
Answer The tested response rises to 30 °C then falls; 30 °C has the highest measured rate.
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.
Calculate the average rate when 2.4 cm³ gas is collected in 4 min at a tested temperature.
Give me a hint
Use gas volume divided by time.
Compare my reasoning
- 2.4 ÷ 4 = 0.6.
- Use cm³/min.
0.6 cm³/min.
Look for these in your work
- Correct arithmetic.
- Correct units.
Compare supplied rates of 0.6 cm³/min at 30 °C and 0.1 cm³/min at 40 °C. State the ratio and absolute fall.
Give me a hint
Use both a ratio and a difference.
Compare my reasoning
- 0.6 ÷ 0.1 = 6.
- 0.6 − 0.1 = 0.5 cm³/min.
The 30 °C rate is six times the 40 °C rate; the fall is 0.5 cm³/min.
Look for these in your work
- Distinguish ratio from rate difference.
- Include units on the difference.
A single 30 °C result is high. Explain why it is not enough to establish the exact optimum temperature.
Give me a hint
Consider repeats and untested temperatures.
Compare my reasoning
- One result may vary.
- Nearby temperatures have not been tested closely.
- Repeat and add suitable nearby settings under control.
Repeat measurements and closer temperature sampling are needed; the supplied result identifies only a promising tested setting.
Look for these in your work
- Name both reliability and sampling.
- Avoid a universal optimum.
Common mistakes
- Do not convert fastest tested into an exact optimum.
- Gas collection and irreversible heat damage need separate checks.
What can you explain now?
Why could reusing a previously overheated plant weaken a later low-temperature comparison?
Compare with the explanation
Earlier heat may have lasting effects.
The new treatment could include a history effect.
After trying it yourself, choose your next review. This is your self-assessment.
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Make it stick
Explain the tested temperature pattern and two ways to strengthen the comparison.
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.