Q12 - C3 vs C4 Photosynthetic Response to Low Temperature

Theoretical A Real exam question - full text reproduced under IBO's CC BY-NC-SA 4.0 license

Calvin Cycle, Photorespiration & C4/CAM Biochemistry

An experiment was carried out on sorghum (Sorghum bicolor) and soybean (Glycine max) plants in response to low temperature. Plants were grown at 25°C for several weeks and then at 10°C for three days, while day length, light intensity and ambient carbon dioxide concentration were kept constant throughout the experiment unless stated otherwise. The net photosynthesis of both plant species at 25°C is shown in Fig.Q12 below.

Carbon dioxide uptake per leaf dry mass (mg CO2 g-1)

Days	before	1	2	3	4-10
Temperature	25°C	10°C	10°C	10°C	25°C
Sorghum	48.2	5.5	2.9	1.2	1.5
Soybean	23.2	5.2	3.1	1.6	6.4

Figure 1. Figure 1.

Using the information and data, determine which of the statements are true or which are false.

A. If put at 35°C, photosynthesis rate of soybean would decrease and that of sorghum would not change.

B. In cool condition, the biomass of sorghum increases faster than that of soybean.

C. Soybean plants are likely to have smaller photosynthetic water use efficiency than sorghum.

D. The reduction of the carbon dioxide uptake in sorghum is mainly due to the decrease of enzyme activity in low temperature.

← Previous: Q11 Next: Q13 →

Question reproduced from IBO 2016, Theoretical Paper A, licensed under CC BY-NC-SA 4.0 - attributed to the International Biology Olympiad. Open the full exam PDF · Community solutions (unofficial)