Science: An Elementary Teacher’s Guide/Food Chain

Food Chain (food web) is a hierarchical series of organisms each dependent on the next as a source of food. Is the order in which living things eat in the ecosystem. The food chain is the path of food energy from one organism to another in an ecosystem.

  • Energy is what is needed to do work or cause change. The source of all energy in a food chain is the sun.
  • Sun- the star at the center of our solar system that supplies heat and light to Earth.

Did you know? Food chains were first introduced by the African-Arab scientist and philosopher Al-Jahiz in the 9th century and later popularized in a book published in 1927 by Charles Elton, which also introduced the food web concept

Food Chain Length

The food chain's length is a continuous variable that provides a measure of the passage of energy and an index of ecological structure that increases in value counting progressively through the linkages in a linear fashion from the lowest to the highest trophic (feeding) levels. Food chains are often used in ecological modeling (such as a three species food chain). They are simplified abstractions of real food webs, but complex in their dynamics and mathematical implications.Ecologists have formulated and tested hypotheses regarding the nature of ecological patterns associated with food chain length, such as increasing length increasing with ecosystem size, reduction of energy at each successive level, or the proposition that long food chain lengths are unstable. Food chain studies have an important role in ecotoxicology studies tracing the pathways and bio magnification of environmental contaminants


also known as autotrophs, is an organism that uses sunlight to make its own food for energy. They make up the first level of every food chain. Autotrophs are usually plants or one-celled organisms. Nearly all autotrophs use a process called photosynthesis to create “food” (a nutrient called glucose) from sunlight, carbon dioxide, and water.Plants are the most familiar type of autotroph, but there are many other kinds. Algae, whose larger forms are known as seaweed, are autotrophic. Phytoplankton, tiny organisms that live in the ocean, are also autotrophs. Some types of bacteria are autotrophs. For example, bacteria living in active volcanoes use sulfur compounds to produce their own food. This process is called chemosynthesis.


Are the living organism who will depend on other organism to survive. The second trophic level consists of organisms that eat the producers. These are called primary consumers, or herbivores. Deer, turtles, and many types of birds are herbivores. Secondary consumers eat the herbivores. Tertiary consumers eat the secondary consumers. There may be more levels of consumers before a chain finally reaches its top predator. Top predators, also called apex predators, eat other consumers. Consumers can be carnivores (animals that eat other animals) or omnivores (animals that eat both plants and animals). Omnivores, like humans, consume many types of foods. Humans eat plants, such as vegetables and fruits. We also eat animals and animal products, such as meat, milk, and eggs. We eat fungi, such as mushrooms. We also eat algae, in edible seaweeds like nori (used to wrap sushi rolls) and sea lettuce (used in salads). 


Are the living organism (bacteria) that will break down other living organism. Detritivores and decomposers are the final part of food chains. Detritivores are organisms that eat nonliving plant and animal remains. For example, scavengers such as vultures eat dead animals. Dung beetles eat animal feces. Decomposers like fungi and bacteria complete the food chain. They turn organic wastes, such as decaying plants, into inorganic materials, such as nutrient-rich soil. Decomposers complete the cycle of life, returning nutrients to the soil or oceans for use by autotrophs. This starts a whole new food chain.  

Example of the Energy Flow in a Food Chain.

  • The sun gives energy to the grass
  • The grass gives energy to a mouse
  • The mouse gives energy to a snake
  • A snake gives energy to an eagle
  • Dead animals and plants give energy to the earthworms (decomposers)

Producer = plants

Consumer = mice

Decomposer = bacteria

For example, grass produces its own food from sunlight. A rabbit eats the grass. A fox eats the rabbit. When the fox dies, bacteria break down its body, returning it to the soil where it provides nutrients for plants like grass.

Any given species that may eat one type of food or multiple species consumers may feed on similar organism. A barn owl might eat a mouse; A mouse could have been eaten by a sparrow hawk, a snake, or any of the numerous other carnivorous animal.

Plants are the first level in the food chain are known as primary producers. Plants and vegetable make their own food and energy through a process called photosynthesis. Plants make their own food by using sunlight, carbon dioxide from the air, and water from the soil and converting it in the form of sugar. There are three levels of consumers primary consumers organisms that eat plants are the plant eaters of the chain Secondary consumers eat the primary consumers. A mouse might be a primary consumer and a cat might be the secondary there is a third level of consumer called the tertiary consumer these are consumers that eat the secondary and primary consumers. A tertiary consumer could be a wolf that eats the cat and the mouse.

Decomposers break down nutrients in the dead stuff and return it to the soil. The producers can then use the nutrients and elements once it's in the soil. The decomposers complete the system returning essential molecules to the producers.