Q30 - Odour Receptors and Neuron Identity in C. elegans

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

The worm C. elegans shows sophisticated behaviour in response to odour. It has 11 pairs of chemosensory neurons. Odours are detected by G protein-coupled receptors (GPCR) on the outside of these neurons. The receptor protein ODR-10 on the neuron AWA initiates the movement of C. elegans towards the odour diacetyl (its location shown as X in figure B). The neuron AWB, however, initiates movement away from the toxin nonanone (A).

A, diacetyl elicits an attraction (+) of the worm via AWA, nonanone elicits a repulsion (–);

Mutant animals don’t express ODR-10. Transgenic animals only express ODR-10 receptors on AWB. The receptor still reacts to the presence of diacetyl, but its reaction is avoidance (–). I, WT = wild type; II, mutant without receptor; III, transgenic animal.

Figure 1. Figure 1.

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

A. ODR-10 on AWA is required for attraction towards diacetyl

B. ODR-10 can mediate both attraction and repulsion

C. Each olfactory neuron has receptors for many odour chemicals

D. All olfactory neurons are functionally similar even if their receptors are different

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Question reproduced from IBO 2015, Theoretical Exam B, licensed under CC BY-NC-SA 4.0 - attributed to the International Biology Olympiad. Open the full exam PDF · Community solutions (unofficial)