Q66 - Comparing Lead Toxicity Thresholds for Growth and Photosynthesis in Two Microalgae

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

Bioenergetics & Central Metabolism Overview

A study on the effects of lead (Pb), a toxic heavy metal, on growth and photosynthesis of two microalgae, Chlorella and Scenedesmus was conducted. The figure on the left below shows the growth of these strains responded differently to lead concentration after 4 day treatment. From growth rate (Ke), generation time (G) of each strain at each concentration of lead can be calculated as equation: G = (ln2)/Ke. The right hand Figure Q.66 is result of the effect of lead on photosynthesis of these strains, indicated by Fv/Fm, a sensitive parameter that decreases when photosynthesis is impaired. The concentration of lead that gives half-maximal response, the IC50, can be estimated based on response versus lead concentration plots.

Figure Q.66

Figure 1. Figure 1.

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

A. Estimated IC50 of growth for the Scenedesmus was higher than that for the Chlorella.

B. Photosynthetic impairment by Pb was likely responsible for the growth decrease in the Chlorella but this was not the scenario in the Scenedesmus

C. The estimated IC50 for effects on Fv/Fm was higher than that for growth in Scenedesmus

D. At lead concentration that Log10([Pb]+1) is 0.5, the Scenedesmus reproduced faster than the Chlorella did.

← Previous: Q65 Next: Q67 →

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)