A food chain is a diagram that shows how energy is transferred from one living thing to another. Energy is transferred from the sun to plants, which use the light to produce energy through a process called photosynthesis. An animal then eats the plant for food, is eaten by another animal, and so on until you reach the top of the food chain.
Plants are called producers because they make their own food and are the starting point of the food chain. Animals are called consumers as they eat plants and other animals and are further up the food chain. If the animal at the top of the food chain has no natural predators, it is called an apex predator.
If one part of a food chain is reduced or altered, the entire food chain is affected. For example, if there were a drought and fewer plants available to eat, the animals that depended on them would survive less well, reducing the food supply for animals further up the food chain.
Quick food chain recap
Food chains are broken down into trophic levels.
Producers
Producers are usually plants, algae or phytoplankton. They use sunlight to create food by photosynthesis.
Primary Consumers
These are usually herbivores that eat producers.
Secondary Consumer
These eat the primary consumers. They are carnivores or omnivores.
Tertiary Consumers and Apex Predators
These are bigger animals that eat the secondary consumers.
Example Food Chains
Grass ( Producer )----> Grasshopper ( Primary Consumer )-----> Frog ( Secondary Consumer ) -----> Hawk ( Apex Predator )
Cactus ------> Desert Mouse -----> Rattlesnake-----> Coyote
Pollution in the Food Chain
Pollution accumulates through a food chain ( biomagnification ). Imagine a farm that's sprayed with pesticides to stop bugs from eating crops. Pesticides leach into the soil and are then absorbed by grass in nearby fields. Cows eat a LOT of grass. Pesticides from the grass build up in the cells of the cow and enter its milk. Humans then drink the milk or eat beef from the cow!
Mercury in Food Chains
Mercury is released into the environment from human activity such as burning coal and, until recently, in insecticides. Mercury released into the air eventually settles into oceans and lakes, where bacteria convert it into toxic methylmercury, which is hard for animals to remove from their bodies.
Plankton ----> Krill ----> Minnows ------> Trout -----> Tuna -----> Humans
Mercury in the Food Chain Activity Sheet
Print my FREE Mercury and the Food Chain activity to make your own food chain.
While a minnow in the food chain above may contain only a small amount of mercury, trout eat a lot of minnows, and tuna eat a lot of trout over their lifetime. Mercury concentration increases up the food chain.
Why is tuna high in mercury but not salmon?
Tuna are apex predators that accumulate mercury by eating smaller fish over many years. Salmon don't live as long and are lower in the food chain.
Mercury builds up in tissues over time ( bioaccumulation).
Last Updated on June 2, 2026 by Emma Vanstone
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