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Q18 - Mycorrhizal Symbiosis - Ecto-, Endo-, and Ectendomycorrhiza

Theoretical 1 Real exam question - full text reproduced under IBO's CC BY-NC-SA 4.0 license
Root Anatomy Mineral Nutrition & Nutrient Uptake

The following schematic image shows a transverse cut of a root, showing symbiosis with 3 different groups of organisms (a, b, and c).

Cross-section of a root split into three sectors (a, b, c), each showing a different fungal symbiosis pattern - external mantle hyphae, internal arbuscules/vesicles/spores, and simpler external hyphae. Root cross-section, split into sectors (a), (b), and (c), each showing a different fungal association: (a) external mantle + hyphae, (b) arbuscules, vesicles, and spores penetrating the cortex, (c) external hyphae with a different branching pattern.

Using the schematic image, determine whether the following statements are true or false.

A. Diagram (a) shows ectomycorrhiza.
B. Diagram (b) shows endomycorrhiza.
C. Diagram (c) shows ectendomycorrhiza.
D. One of the diagrams indicates a symbiosis of nitrogen-fixing bacteria and plant.
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Question reproduced from IBO 2022, Theoretical Paper 1, licensed under CC BY-NC-SA 4.0 - attributed to the International Biology Olympiad. Open the full exam PDF · Community solutions (unofficial)