Solution:

The endocrine system is an organ system that controls and coordinates all activities in the body. This system includes endocrine glands and their secretions called hormones. Hormones are chemical messengers that regulate cellular activities.

Chemical substances that are secreted by certain animals to the surroundings to facilitate communication are called pheromones. Pheromones help in attracting mates, informing the availability of food, determining the path of travel, signalling dangers etc.