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Q61 - Cadmium's Effect on Maize Root Elongation and Endodermal Suberization

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

To study the effects of cadmium (Cd) on root development, two experiments on maize seedlings with 6-cm-long root were conducted. First, seedlings were grown either in media supplemented with 5 µM Cd (Cd5) or without Cd (Cd0). Second, seedlings were grown either in two layers of agar without Cd (Cd0-Cd0) or unilaterally to 100 µM Cd (Cd0–Cd100). Four days later, root growth was recorded (Figure Q.61-1) and cross-sections of roots were stained to visualize suberin lamellae in endodermis (Figure Q.61-2, sections correspond to cut sites from Figure Q.61-1).

Figure Q.61-1. Distance from root apex to root base as obtained from experiments 1 (A) and 2 (B). The regions of mature endodermis in the roots are shown as solid and dashed lines.

Figure Q.61-2. Cross sections at position marked in Figure Q.61-1. White arrows indicate suberin lamellae in the endodermis.

Figure 1. Figure 1.

Figure 2. Figure 2.

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

A. The treatment of Cd resulted in the reduction of elongation zone of the root, leading to decreased root length.
B. Endodermal cells with suberin lamellae were already present at a distance of approximately 0.5 cm from the root apex in tissues adjacent to agar containing Cd100, however, suberinized cells were found much further from the apex on the other side.
C. In roots exposed unilaterally to Cd (Cd0-Cd100), the development of the endodermis was accelerated and asymmetrical.
D. In high Cd containing media, suberin lamellae in endodermal cells were not present in older parts of the root likely due to the restriction of Cd in younger part.
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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)