Q64 - Diurnal Light and CO2 Co-Limitation of Underwater Photosynthesis

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

Photosynthesis of submerged aquatic plants is severely impeded by many environment factors. In seawater and freshwater, light density and its spectrum is changed with depth in the water column and thus influence photosynthesis. Other factors affecting photosynthesis include level of carbon dioxide (CO2) and oxygen (O2).

Swamp Raspwort (Meionectes brownii) is a wetland plant species but can grow as a submerged aquatic plant in freshwater. An experiment was conducted to study the photosynthesis of the aquatic vegetation. Diurnal fluctuations in surface irradiance, partial pressure of O2, CO2 concentration and pH of the water in Swamp Raspwort- rich ponds are shown in Figure Q.64.

Figure Q.64

Figure 1. Figure 1.

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

A. In the underwater of ponds, light limitation appears early in the morning and co-limitation of both light and CO2 takes place early in the afternoon.

B. The decrease in level of O2 in water column during the night is caused by the Swamp Raspwort respiration.

C. In water column of ponds, CO2 molecules are directly produced by respiration of Swamp Raspwort and by conversion from HCO3- at pH neutral results in increasing CO2 level.

D. As indicated in the figure, temperature variation in ponds rich Swamp Raspwort is from 13 to 20°C. The alteration in temperature is mainly maintained by high density of this plant species.

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