Pheromones: These are chemical signals released by animals and plants to communicate with other individuals of the same species. Examples include androstenone released by male pigs to attract females, and citronellal released by queen termites to signal to others that she is the queen.
Alarm substances: These are chemical signals released by some organisms to signal danger. Examples include quinones released by ants when under attack, and alarm pheromones released by fish to signal the presence of a predator.
Plant hormones: These are small molecule signals released by plants to regulate their growth and development. Examples include auxins and gibberellins which regulate cell elongation and other developmental processes.
Neurotransmitters: These are small molecule signals released by neurons in the brain to communicate with other neurons. Examples include serotonin, dopamine, and glutamate which are involved in various functions including mood, movement, and learning.
