For the ecosystem to function energy must be available and it must be transferred. Why? Because of the First and Second Laws of Thermodynamics. The First Law states that energy can neither be created nor destroyed, but can be converted from one form to another. The Second Law states that everything is running downhill or, more formally, everything in the universe is going from a more organized state to a less organized one.

To illustrate these laws, let's consider a car with a full tank of gasoline. The gasoline is burnt, the car goes, and the gasoline is broken down into gases and heat, but, following the First Law, the total amount of energy is constant although now it is in a different form, namely heat. Heat is a very disorganized form of energy. However, what of the Second Law? It, too, has been operating.

Life exists because it has found a way to reverse the Second Law of Thermodynamics, if only temporarily, but, to do this, living things need constantly to invest energy. There is, however, only one energy source available to earth’s organisms and that is the sun. Photosynthesis is the only means available to use this source energy. Autotrophs are organisms that produce their own food through photosynthesis.

Heterotrophs are organisms that consume autotrophs and use the energy of their bodies to survive. The transfer of energy from the autotrophs to the heterotrophs always involves the conversion of some of the energy into heat. Only a small percentage of the energy of the autotrophs is actually used. For example, a flock of birds descends on a bush and eats its berries, but 98% of what is eaten is excreted as water and other waste or converted to energy. In addition, the bird becomes food for other organisms.

Any ecosystem can be viewed as consisting of producers (the autotrophs) and consumers (heterotrophs). These concepts are the bases of the ECOSYSTEM PYRAMID OF ENERGY.

The autotrophs form the basis of the pyramid and are the primary producers. The next level is heterotrophs that consume the autotrophs and are the primary consumers. Generally, 10% of the energy is based from one level to the next.
 

Decomposers that break down the remains of plants and animals also figure into pyramid of energy. Detritus food chains transform litter back into nutrients.

Each level in an energy pyramid is called a trophic level and all transfers of energy involve the conversion of some energy into heat.
This means that the energy of each higher trophic level is smaller than the one below it. All energy pyramids are broadest at the base.

There are also PYRAMIDS OF NUMBERS that tell you the actual numbers of organisms at various levels and PYRAMIDS OF BIOMASS are related to the amount of chemical energy. See example below:
 

FOOD WEBS illustrate the complex interaction of organisms in the various pyramids. The movement of energy from one trophic level to the next or through the food web is shown in the ENERGY-FLOW DIAGRAM.

Photosynthesis limits productivity of the ecosystem. The net primary production is the gross production minus the energy and carbon compounds lost by plant respiration. The factors that limit primary productivity are temperature and water, mineral nutrients, light and carbon dioxide.

Definitions:

1. Autotrophs - Organisms that produce their own food through photosynthesis.
    
2. Consumers - Organisms that consume other organisms for food.
    
3. Decomposers - Organisms that break down the remains of plants and animals.
    
4. Detritus food chain - Transforms litter into nutrients.
    
5. Energy-flow diagram -The movement of energy from one trophic level to the next.
    
6. Energy pyramid - The flow of energy from the producer through the various consumers.
    
7. Food webs - Diagrams illustrating the complex interaction of organisms in an ecosystem.
    
8. Heterotrophs - Organisms that consume autotrophs or other heterotrophs for food and use their energy.
    
9. Producers - Organisms that carry on photosynthesis and, thus, create their own food.
    
10. Pyramid - A diagram illustrating the flow of a commodity through the ecosystem.
    a) Pyramid of biomass - A pyramid based on chemical energy.
    b) Pyramid of numbers - A pyramid based on the number of organisms involved at various levels.
     
11. Trophic level - Each level in an energy pyramid.

Experiments for Home and Classroom

You can try these desert experiments at home. You can create a mini-pond at home and grow your own algae, see how cyanobacteria grow mostly in the warm, upper layers of a lake or see how warm temperatures speed up bacterial growth. Desert plants grow better in the heat than plants imported from colder places. See how plants require the right temperature in order to grow. A little bit of air or water, pollution goes a long way. Find out how.
http://chainreaction.asu.edu/ecology/trythis/

Here are 12 ecology-related experiments for you to try:
Before starting any of the experiments listed be sure to read the instructions carefully.
http://www.galeschools.com/environment/experiment/index.htm

Build a small ecosystem and make a mold terrarium, watch tiny blue, green and white plants grow on leftover food.
http://www.exploratorium.edu/science_explorer/mold.html

Create this your own food chain and energy pyramids
http://www.vtaide.com/png/foodchains.htm

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