Food chains start with plants because they are the only organisms that manufacture their own food. All other organisms get their food by either eating plants or feeding on others in the food chain.
The food chain, which is sometimes called a food web, starts with plants because they are the producers. Plants are called producers because they use energy from the sun to make their own food through a process called photosynthesis. Plants make a variety of nutrients which are responsible for supporting healthy life for both animals and human beings.
Right after plants, a food chain consists of primary consumers which are organisms that basically feed on plants. These organisms include things like antelopes, squirrels, elks or any other animals that feed exclusively on plants. Another term for primary consumers is herbivores.
Right above primary consumers are secondary consumers which are organisms that feed on primary consumers. These organisms are sometimes referred to as carnivores which is another term for flesh eaters. Examples of secondary consumers include cats, cheetahs, leopards and tigers.
Right above secondary consumers are tertiary consumers who are able to feed on secondary consumers, primary consumers and producers. These are sometimes referred to as omnivores and include human beings and bears.