1. What is the primary mechanism of action for organophosphate poisoning? A. Inhibition of cyclooxygenase B. Blockade of GABA receptors C. Inhibition of acetylcholinesterase D. Activation of nicotinic receptors Answer: C. Inhibition of acetylcholinesterase Rationale: Organophosphates exert their toxic effects primarily through the inhibition of acetylcholinesterase, leading to an accumulation of acetylcholine in the synapses. 2. Which principle of toxicology states that the toxicity of a substance is dependent on its concentration or dose? A. Principle of individual exposure B. Principle of dose-response C. Principle of cumulative risk D. Principle of threshold effect Answer: B. Principle of dose-respon