Animals become active on seeing the food. 

Yes, it is true that many animals become active or exhibit increased activity levels when they see or smell food. This is because food is a primary motivator for most animals, as it is necessary for their survival and provides them with the energy and nutrients they need to grow, reproduce, and carry out other activities.

When animals detect the presence of food, they may exhibit a range of behaviors that are designed to help them obtain or consume it. For example, predators may become more alert and begin to stalk or chase their prey, while scavengers may become more mobile and start to search for food in new locations. Herbivores may also become more active when they find a source of food, such as a patch of grass or a fruit tree, and may spend more time feeding or foraging in that area.

Overall, the response of animals to food is a complex and multifaceted phenomenon that is influenced by a wide range of factors, including the availability and quality of food, the competitive and social dynamics of the animal's environment, and its own physiological and metabolic needs.