Although we concentrate in this chapter on olfaction and gestation in multicellular animals, other organisms detect external chemical signals in other ways that we can briefly mention (again acknowledging that our singling out of animal taste and smell as separate senses is somewhat arbitrary and artificial relative to chemosensation in the world as a whole). Plants do not have sensory systems equivalent to taste or smell but they do respond to external chemical signals including by differential growth corresponding to chemical gradients in the environment, ripening induced by ethylene, responses to herbicides, and the like.
Single-celled organisms respond to chemicals as well. As mentioned in Chapter 12, planktonic Dictyostelium discoideum induce aggregation among their peers by emitting a chemical signal and as aggregates they respond to environmental chemicals, particularly ammonia, in various ways. E. coli and Salmonella, and many other single celled organisms, navigate toward and away from chemical attractants or repellants, for example, toward nutrients or away from toxins.
Was this article helpful?