A food chain is a simple sequence of organisms in which each animal or plant is dependent on the one above or below it. Food webs are more complex than food chains in that they include all organisms that have similar feeding habits. Both food chains and food webs include animals that depend on each other for food.
The food chain is rare in nature, but it is a useful concept that allows scientists to study the relationship between different plants and animals.
Food webs are organized into three categories, or trophic levels, which are the producers, consumers and decomposers. Producers make their own food and are called self-feeders. For instance, green plants are producers, making their own food using sunlight in a process called photosynthesis.
Consumers cannot make their own food and have to eat other organisms to get the nutrients they need. Consumers can be divided into three groups. Herbivores are the plant-eating animals and carnivores are the meat-eating animals. A third group called omnivores eats both plants and animals.
Consumers are also classified as primary, secondary and tertiary. The herbivores are the primary consumers. Animals that eat the primary consumers are called secondary consumers. The third order, or tertiary consumers, eat the secondary consumers.