Q29 - Rhizobial Nitrogen Fixation Symbiosis
Nitrogen is an important nutrient for all plants. While there is an abundance of nitrogen (N2) in the atmosphere, most plants are unable to convert N2 into a usable form. Fixation of nitrogen gas into ammonia is an ability restricted to nitrogen-fixing bacteria. The figure below shows prerequisite step for nitrogen fixation through symbiosis between these bacteria and some plant species.
Figure 1.
Using the information and data, determine which of the statements are true or which are false.
A. Between two major inorganic nitrogen forms, NH4+ and NO3-, the former is mobile in the plant, while the latter is not.
B. Immediately after recognition of plant by bacteria and recognition of bacteria by host plant, a calcium spike occurs in the root cells.
C. The plant hormone cytokinin is needed for initiation of nodule formation.
D. Release of bacterial exopolysaccharides is the necessary and sufficient condition for a functional symbiosis between rhizobia and its appropriate host.
Question reproduced from IBO 2018, 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)