Life Cycle - Natural Environment (4B)
Post Lab 

  • Examining a fresh water aquarium ecosystem.
  • Differentiating a food web and a food chain.
  • ecosystem
  • food chain
  • food web
  • photosynthesis
  • primary consumer
  • secondary consumer
  • work sheet
  • aquarium (optional)

Students use a worksheet to describe an ecosystem. 


An ecosystem illustrates the relationship of plants and animals with each other and with the environment.  Ecosystems can be as large as the ocean or as small as an aquarium.  The only factor in determining an ecosystem is the exchange of nutrients, gases, or processes that aid or overcome another organism.  Simply, an organism will help another one to survive by doing something essential to the other's survival or to survival of the environment, or will simply kill or eat the other.  Irrespective of the size of the ecosystem, plants and animals will continuously live in a never-ending cycle of life.

The first step in the ecosystem begins with the Sun.  The majority of primary producers are plants whether they are in, the water or on land.  Plants use  the energy from the sun to produce food in the form of simple sugars.  Photosynthesis, is very vital to the survival of animal life.  Animals depend just as much on photosynthesis as plants do.  The plants that produce sugars by photosynthesis are called producers.  The producers are then eaten by several different kinds of organisms.  The animals that eat primary producers are called primary consumers.  In the water, fish and other animals eat tiny green plants called algae.  The algae are primary producers and the animal and fish are consumers.

As the cycle continues, the small fish that eat the algae will be eaten by larger fish.  This cycle that exists from producer to different consumers is called the food chain.

  1. Discuss with students the food chain and food web.
  2. If you have an aquarium in your classroom, you may want your students to use that instead of the worksheet.  The purpose of this worksheet is to determine the food chains that might be in an aquarium.  For instance, in the worksheet one food chain is: Sun - algae - protozoa - insect - fish.  Ask the students if there are more than one food chain in the aquarium?  Yes, another food chain would be Sun - algae - newt.  Sun-algae -snail - fish, may be another food chain.  Together they create a food web, which also takes into account that the fish might actually eat the poop of the snail.  Food webs can be intriciate.
  3. If you discuss a real aquarium, you would have to discuss the different types of fishes because some fish eat other fish.  Also, when fish have babies, they are usually eaten by bigger fish.  

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