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Earth Science Lesson 5
Ecology (Grade 6)


Instruction 5-1

Energy Transformation in the Ecosystem | The Food Web and the Physical Environment | Organism Populations | Biomes | Resources in the Ecosystem | Summary

Energy Transformation in the Ecosystem

CCSTD Science Grade 6 5.a. 

In our last two Lessons, we learned that almost all of the energy we use on Earth comes from the Sun. How can that be? We don't eat sunshine, do we? Well, actually we do, but it has to be turned into food first. This Lesson is about how that happens. First, however, we need to tell you a little about ecology. 


Ecology is the study of the relationships among organisms and the environments in which they live. This includes all living (biotic), non-living (abiotic) and anthropogenic (man-made) components of the environment. 

Biotic (living) components include organisms such as plants, animals and microorganisms.

Abiotic (non-living) components include weather, temperature, light, water, inorganic nutrients and soil.

Anthropogenic (man-made) components include anything introduced into the environment by human beings. One example would be the carbon dioxide released when we burn certain kinds of fuel.


The word ecosystem is short for "ecological system." What makes an ecosystem is the relationship of all the ecological components within a specific area. In other words, an ecosystem is a functional unit that results from the interaction of all its biotic, abiotic and anthropogenic (cultural) components. (Also see: http://www.eco-pros.com/).

There are many different levels of ecosystems. An ecosystem could be huge, such as the Global Ecosystem, which includes all the organisms living on Earth, the Earth itself (both land and sea) and the atmosphere above the earth.

Or it could be as small as a Freshwater Pond Ecosystem, which includes the plants, animals and microorganisms that live in the pond, the pond water, all the substances dissolved or suspended in that water, and the rocks, mud and decaying matter that make up the pond bottom. Energy and nutrients always pass through organisms in a specific sequence, which we'll tell you about shortly, but first we need to acquaint you with some ecological terminology: 

  • Habitat is where an organism lives (such as "under a log"). A habitat must supply an organism's needs, such as food, water, temperature, oxygen and minerals. If it doesn't, the organism will move to a better habitat.

  • Population is a group of living organisms of the same kind living in the same place at the same time.

  • Community is the interactions of a population.

  • Niche is the role of an organism in its community (including the factors that maintain its life, such as how it acquires food).

  • Symbiosis is the relationship between two different organisms that co-exist (and in some cases help each other to survive).

  • Producers are green plants, bacteria and algae that transform the Sun's energy into usable energy for them, and for the rest of the living organisms in an ecosystem. 

  • Herbivores are animals that eat plants (sometimes called Primary Consumers). 

  • Carnivores are animals that eat other animals (sometimes called Secondary Consumers). 

  • Omnivores are animals that eat both plants or animals (like brown bears and human beings). 

  • Decomposers are bacteria, fungus and tiny creatures (like maggots and dung beetles) that eat dead plants and animals. You know about decomposers if you watch TV crime shows like CSI or Forensic Files. Decomposers not only keep the environment clean, they also can be very helpful in establishing when something or someone died. 

  • Predators are animals that hunt, kill and eat other animals for food. 

  • Prey is the animal that predators kill for food. 

  • Biomes are ecosystems where several habitats intersect, like Earth. Smaller biomes include deserts, tundras, grasslands and rainforests.

  • Biosphere is the Earth's landmasses, oceans and atmosphere, as well as all the animals, plants, insects, birds and other organisms living in them.

Now that you know the setting and the cast of characters, it's time to see how the "transformation of energy" story plays out.


As you know, all life on Earth begins with the Sun. Plants use energy from the Sun to make food for themselves and for the animals that eat them, but they only use a little of the Sunís energy. Between 1 and 10 percent of the Sun's energy that reaches the Earth is transformed through the food chain, which begins with a process called photosynthesis. Hereís how Photosynthesis works:

A plant takes in carbon dioxide (C02) from the air thorough its leaves, and it takes in water (H20) from the soil through its roots. Then, a green pigment in its leaves called chlorophyll uses the energy from the Sun to convert the carbon dioxide and water into glucose (C6H1206). Glucose is a kind of sugar. It is the basic food for the plant itself and for the animals that eat it. 

The chemical equation for photosynthesis is:  6H20+6C02------------->C6H1206+602.

The explanation is: Six molecules of water plus six molecules of carbon dioxide plus sunlight (energy) yields six molecules of glucose (sugar) plus six molecules of oxygen.

What happens next? We'll tell you all about it in our next Instruction. 

Video Instruction
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Energy Transformations [2:38]

Experiments for Home and Classroom

One of the most important energy transformations in any ecosystem is photosynthesis, the process by which plants turn sunlight into energy (food).

This experiment demonstrates the process quite effectively, although it was originally designed for younger children. The plant required, elodea, is also called "water weed" and is widely used in aquariums, so it is available anywhere that sells aquarium supplies. Elodea is an important part of lake ecosystems, providing safe haven for young fish and amphibians and food for ducks and beavers.

These photosynthesis experiments demonstrate why leaves change color in the fall. Scroll down to "Projects" and don't be put off by the big word "chromatography": it simply means classifying things on the basis of their chemical differences.

Here, courtesy of the Boy Scouts of America, is an interesting series of "Natural World" experiments, including an experiment on "Watching Plants Grow."

This web site is called "Bizarre Stuff You Can Make in Your Kitchen." Although not really that bizarre, the plant-growing experiments look like fun. Click:

Reading List:
from the California Department of Education

Title, Author



The Eternal Darkness (Exploration of a Deep Ocean Ecosystem by the Man who Discovered The Titanic) (Ballard, Robert)

On the Day You Were Born (Explanations of a Wide Range of Natural Phenomena, including Photosynthesis) (Frasier, Debra)

for Students, Parents and Teachers

Now let's do Practice Exercise 5-1 (top).

Next Page: The Food Web and the Physical Environment (top)