Biological signals are chemical or physical cues that organisms use to communicate and respond to their environment. These signals can include hormones, neurotransmitters, and pheromones, which help regulate processes like growth, reproduction, and stress responses. For example, when a plant senses light, it produces hormones that direct its growth toward the light source. In animals, biological signals play a crucial role in behaviors such as mating, foraging, and social interactions. Neurotransmitters in the brain transmit signals between nerve cells, influencing mood and behavior. Similarly, pheromones released by one individual can affect the behavior of others, facilitating communication within a species.