What is a Food Chain and A Food Web

Summary

What is a Food Chain?

The Food chain represent the flow of energy and nutrients from one organism to another through the ecosystems. The food chain is a representation of who eats whom relationship. The food chain show a linear pathway. In reality, we cannot always show this in one linear pathways, because some organisms have several food sources.

This boy is eating a hamburger. One linear pathway to show this would be:
grass –> cow –> human.
However, the boy also has vegetables in his hamburger. Another linear pathway is:
lettuce –> human; or tomato –> human

A food web consists of many intersecting food chains and represents the different things an organism can eat and be eaten by.

Autotrophs or Producers

All food chains start with plants and end with animals. Autotrophs or producers are self-feeders. They can make their own food. Plants use energy from sunlight to make their own food. Plants need energy in order to live.

Algae and cyanobacteria are examples of producers.

Autotrophs are the foundation of every ecosystem on the planet. Based on how they capture light or chemicals to sustain their survival, their role in the food chain are producers. Thus autotrophs or producers are also called primary producers.

Heterotrophs or Consumers

Consumers or heterotrophs are other-feeders. They eat other organisms or their byproducts

Animals, fungi, many bacteria and humans are all consumers.

Consumers may be plant-eating insects (herbivores), meat-eating animals (carnivores), or fungi that feed on debris and wastes. Herbivores that eat primary producers are called primary consumers. Organisms, meat-eater or carnivores, that eat primary consumers are called secondary consumers. Likewise, organisms that eat secondary consumers are called tertiary consumers.

Eagles are tertiary consumers, carnivore-eating consumers.
Here is an example of that food chain.

Decomposers

Organisms that break down dead organic material and wastes (from decaying plants, or deceased animals) are called decomposers. Fungi and bacteria are decomposers.

Earthworms, crabs, slugs, vultures, detritovores. feed on dead organic matter. They play an important role in the ecosystem and feed on dead organic matter, making it available for bacterial or fungal decomposers.

Discussion questions:

  1. Earthworms are a sign of soil that should be good for growing plants. Explain why you think this is.
  2. Bacteria are added to human waste at sewage treatment plants. Why do you think this is done?

Trophic Levels

At the bottom of every food web are the producers. When you move upwards, first the primary consumer, then the secondary consumer, and then tertiary consumers. Assigning an organism to a level is not always straightforward. Omnivores are plant-eating and animal-eating organisms. Omnivores eat organisms from more than one trophic level.

Humans eat both plants and animals.

The consumer at the top of the food chain are called apex consumers.

Construction of a Food Web and Food Chains

A Food web is a complex illustration of the relationship of the feeding relationships among common animals. Energy is passed from one organism to another. You will be able to identify lateral relationships within a food web.

Above illustration shows a food web.

Observe the transfer of energy in the food web and then observe the food chain below..

Video – Review

Worksheet