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Energy Transfers From Life to Life

Food Chains and Food Webs

Every life must have a continual supply of energy or it will die. 

  Plants, algae, cyanobacteria and some archaea get their supply of energy directly from sunlight.
  All organisms that are not green must eat other organisms to get the energy they contain. 
  The many kinds of lives that share the earth live by eating each other.

Life on earth is a system of Energy Transfer and Sharing

  In human terms, transferring energy is called
"making a living."

  As living things on Earth make their livings, chemical energy transfers from life to life to life.
  This transfer is called a food chain. (Each step in the food chain is called a trophic level.)

a simple food chain

Food chains always begin with something green that produces chemical energy.

The plant is usually only partially eaten, and does not die.

Example: Grass in a pasture is a Producer.

Link Two in all food chains is an organism that eats green things to use their energy.

Example: A cow grazing is a Consumer.

Link Three in some food chains is a Predator Consumer that eats other Consumers.

Example: You eat a steak.


But Link Three in other food chains involves no killing.


Example: You eat cheese made from cow's milk





Plant Eaters (herbivores) come in many shapes and sizes.

Much plant eating is done by grazers and browsers, mostly mammals, but also by reptiles, birds, and some invertebrates.
Most plant eating is done by insects like grasshoppers.

Predators (carnivores) come in many shapes and sizes.

Cougar hunts the land. Nautilus hunts the ocean. Blue Darner hunts the sky.



Energy is re-packaged as it transfers along a food chain.

Most food chains are only three or four links long. One food chain in a pond community might be (1) algae eaten by a (2) snail eaten by a (3)painted turtle. Three links. 

But say the turtle dies of old age. A (4) crayfish eats part of it. (5) Bacteria and fungi eat the rest of it--they decompose the turtle to get the energy left in its body. Five links.

Since all lives end in death, we can say that all food chains end with bacteria and fungi, the primary decomposers.

Real life is never as simple as the idea of food chains suggests. Instead, the lives in any natural community are a complex system that creates many changing food chains and transfers energy from life to life in all sorts of ways. A grasshopper may be eaten by any of several different bird predators, for example.

• We call this complex combination of energy transfers a food web

An actual foodweb showing all the energy transfers taking place is much more complex than what is shown. The diagram just suggests a few possibilities.

At every link in a food web, 90% of the energy is lost. Consumer Cow is only able to use ten per cent of the energy in Producer Grass. 

Give yourself a quick test. What does this pyramid show?

Energy does not cycle through a community as life-materials do. It does transfer from life to life, but it gets used up. 90% of the energy is lost at each feeding (trophic) level

Then plants and sunlight do their magic photosynthesis again and make more food. 

Review: Producers (plants) are partially eaten by consumers1 (grazing animals), which are sometimes eaten in turn by consumers2 (carnivores), which, when they die are eaten by the decomposers.

At the end of all food chains the energy has been used up, and is replaced by new input of radiant energy from the sun. So energy flows in straight lines through a community and is lost, but is continuously restored to the community by plants, algae, and other photosynthesizers. 


  Energy travels in straight lines through food chains and webs and is used up and is replaced by photosynthesis using sunlight
  Nutrients (Life-Materials) travel in circles that do not end. Nutrients have been recycling on Earth for billions of years.


See if you can label this pyramid with the members of additional food chains.
Put yourself in one chain. 


Energy Transfer is Energy Sharing

When we see Earth-life as a whole system (the Biosphere), we think first of the whole rather than of its individual parts. So when a mouse is eaten by a hawk, we can see that first as an energy transfer within the whole system of life. 

All lives stay alive on energy transfers and end in death.

When we look at the whole system of the Biosphere, we have choices about how we see it: 

• we can choose to see it as a horrible tragedy, a slaughterhouse, or

• we can choose to see it as a system of energy sharing which is essentially cooperative. 

All life on Earth survives by feeding on other lives and their leftovers. We live by eating each other. That is the way things are. What is good for the health of the system is not necessarily good for individual lives within that system.

We have to be cautious here about imposing our human moral judgments onto other lives. We don't find it especially ugly when a carrot dies. But when the rabbit who ate the carrot dies, it can be ugly (to humans). 

If the rabbit was smeared across a highway by a car, that is ugly. If the energy the rabbit contains is not used by other lives, that may look ugly and wasteful. 

But in fact, life is so resourceful that living things always find a way to make a living from whatever is available. What the car did was to shorten the food chain. The crow was happy with the meat he carried back to his nestlings, the sparrow was happy with the fur lining her nest, and forty billion bacteria were living the good life in what was left. 

Explore Further in Energy

  Energy: How Organisms Make a Living
  Energy: Introduction

Explore the Biosphere

Biosphere: Introduction
Biosphere as Place: Introduction
Biosphere as Ocean: Life Zones
Biosphere as Ocean Floor: Benthic Biomes One
Biosphere as Ocean Floor: Benthic Biomes Two
Biosphere on Land: Terrestrial Biomes
Biosphere on Land: Anthropogenic Biomes
Biosphere as Process: Introduction
Biosphere Process: Floating Continents, Tectonic Plates
Biosphere Process: Photosynthesis
Biosphere Process: Life Helps Make Earth's Crust
Biosphere Process:
Rock Cycle--Marriage of Water and Rock
Biosphere Process: Marriage of Wind and Water
Biosphere Process: Gas Exchange
Biosphere as An Expression of Spirit
The Ecological Function of Art
The Earth Goddess
The Tree of Life
The Green Man
Earth Art
Biosphere as Community
Biosphere Microcosm: Bacteria and Archaea
The Procaryote Domain
Biosphere Microcosm: Germs
Biosphere Community: The Eucaryote Domain
Biosphere Community: Protists 1: Algae
  Biosphere Community: Protists 2: Protozoa
Biosphere Community: Plants: What's New?
Biosphere Community: Kinds of Plants--Major Groups
Biosphere Community: Plant Defense
Biosphere Community: Plant Pollination
Biosphere Community: Plant Seed Dispersal
Biosphere Community: Kingdom Animals
Biosphere Community: Kingdom Fungi
Biosphere Community: Six Great Extinctions
Return to Ecology Index


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