Identify the relationship between temperature and CO₂ absorption shown in both graphs.

The line on each graph indicates the mean net photosynthesis rate. Calculate the difference in net photosynthesis at 34°C between plants grown at 400 ppm and 700 ppm CO₂.

Compare the data for the sour orange trees growing at 400 ppm with those growing at 700 ppm.

Identify, with a reason, whether CO₂ concentration or temperature is the limiting factor on photosynthesis at a temperature of 34°C and 400 ppm CO₂.

State two products that pass from the light-dependent to the light-independent stages of photosynthesis. 

1. ..................................................................

2. .................................................................. .

negative correlation / as temperature increases the CO₂ absorption decreases / inverse relationship

4.6(μ mol m⁻² s⁻¹)
Accept answers in the range of 4.3(μ mol m⁻² s⁻¹) to 4.9(μ mol m⁻² s⁻¹).

both show a decrease in CO₂ absorption/net photosynthesis as temperature rises;
at each temperature the 700 ppm CO₂ sample shows greater rate;
at higher temperatures the 700 ppm CO₂ sample can continue to photosynthesis / at higher temperatures the 400 ppm CO₂ sample loses CO₂/goes to net respiration;
the 700 ppm CO₂ trendline/net photosynthesis is (slightly) steeper;
at high temperatures/above 43°C CO₂ absorption at 400 ppm CO₂ goes below zero while it never goes below zero at 700 ppm CO₂;
more variation/greater scatter of results at 700 ppm CO₂; (accept converse)

carbon dioxide is a limiting factor at 400 ppm CO₂ as rate increases at same temperature with increased CO₂

ATP and NADPH₂/NADPH+ H⁺ (both needed)

Most correctly stated that there was a negative correlation in (a).

Many candidates carried out the calculation in (b) correctly.  

Often 2 marks were awarded for (c) but seldom 3. Candidates saw that both show a decrease in net photosynthesis as temperature rises and that at each temperature the 700 ppm CO₂ sample shows a greater rate. Only stronger candidates were able to get a third mark. 

Most candidates saw that CO₂ was the limiting factor in (d) and why.

There were many wrong answers to part (e) which was a recall question from the syllabus.