A. tertiary consumer. just kinda count out, first thing, if a plant is a producer, then consumer, secondary consumer, tertiary, so on so forth
Receptors are typically specialized to react to specific stimulation by initiating a chemical or biochemical (in the case of biochemistry) change. In the field of pharmacology or biochemistry, receptors are usually a protein molecules and the change it undergoes are usually specific to the type of stimuli or signal it is responding to.
Pesticides may end up in water sources (such as rivers and the sea), as a consequence they end up in the food chain. Not only this, human water systems could be affected, resulting in humans ingesting these pesticides.
Pesticide presence increases as you go up the food chain because more food will be consumed (e.g: The larger fish may eat several small fish who are contaminated with the pesticide).
Example:
Algae (absorbs pesticide)—> small fish —> Larger fish —> Human
Hope that helped <3
Explanation is in the file
tinyurl.com/wpazsebu