Describe the pattern of CO₂ uptake in the control plants.

Outline the effect of increased carbon dioxide concentration on CO₂ uptake.

Discuss how CO₂ uptake in this investigation may be affected by other limiting factors.

a. constant/low increase in February and early March;
b. increasing to a peak in late March;
c. decrease throughout April;

a. increased CO₂ leads to greater (rate of) photosynthesis;
b. greatest effect on March 30th;
c. smallest effect on April 28th;
d. effect is not constant / difference varies;

a. temperature/light intensity may be limiting factors;
b. temperature on sample days may have affected (rate of)photosynthesis/higher temperatures may increase (rate of) photosynthesis / vice versa;
c. light intensity may have affected (rate of) photosynthesis in earlier days/higher light intensity for longer may increase (rate of) photosynthesis / vice versa;
d. water/rainfall must be same for both groups;
e. control and test plants must be grown under the same conditions/other named abiotic variable;

7(a) was well answered.

Few recognized in (b) that there was not a constant difference between control and experimental plants.

In 7(c) the majority of candidates failed to relate their answers to the data presented, although they did get credit for some knowledge of limiting factors.