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Energy Flow inEcosystems

All organisms require energy to stay aliveand function.

The source of almost all of this energy isradiant energy, which is the energyradiated from the Sun.

Earth is being continuously bombarded withboth invisible radiant energy, (such as UV),and visible radiant energy (light energy).

About 70% of the radiant energy is absorbedby the hydrosphere and lithosphere andconverted to thermal energy.

Thermal energy is what warms the atmosphere,evaporates water and produces winds.

The remaining 30% of the radiant energyis reflected directly back into space.

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A small fraction of the radiant energy (0.023%)is absorbed directly by living organisms in aprocess called photosynthesis.

Thermal energy keeps Earth’s surfacewarm, but it cannot provide organisms withthe energy they need to grow and function.

Light energy can be used bysome organisms, but itcannot be stored and it is notavailable during the night.

In contrast, chemical energycan be stored in cells and thenreleased when needed.

Chemical energy is used by all organismsto perform functions, including movement,growth and reproduction.

However, as chemical energy is used,it must be replaced…

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Many organisms are able to convertlight energy into chemical energyusing the process of photosynthesis.

This conversion of energy is one of the mostimportant chemical processes. Without it,most life on Earth would not exist!

Organisms that photosynthesize maketheir own energy-rich food compoundsusing light energy.

These organisms are called producers.

On land, the major producers are greenplants. The green colour comes from achemical called chlorophyll whichcaptures light energy.

In aquatic ecosystems, the mainproducers are microscopic organisms.These single-celled algae andcyanobacteria also contain chlorophyll.

Virtually all of the chemical energycontained in food was once lightenergy captured in the process ofphotosynthesis.

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Most producers use light energy to convert low-energy chemical compounds (carbon dioxide andwater) into high-energy compounds (sugars).

PhotosynthesisIn doing so, they release oxygen gas intothe environment as a by-product.

Photosynthesis can be represented bythe following word equation:

carbon dioxide + water sugar + oxygenlight energy

The sugar formed in thisprocess contains storedchemical energy.

This energy is stored in theroots, stems, leaves andseeds of plants.

Photosynthesis

Not all of the sugar produced through photosynthesisgoes towards energy storage. Some sugars are usedas building materials to form carbohydrates or proteins.

Cellular Respiration

Photosynthesisproduces storedenergy in theform of sugar.

To make stored energy available for use,the plant performs a complementaryreaction called cellular respiration.

Cellular respiration is a chemical processin which energy is released from food.

In this process, the sugar and oxygen arerearranged to form carbon dioxide andwater.

Cellular Respiration

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As this reaction takes place, energy isreleased. The plant is able to use thisreleased energy for any of the activitiescarried out by its cells.

The word equation for cellular respiration is:sugar + oxygen carbon dioxide + water + energy

Cellular Respiration

The energy originally stored in the sugar isreleased as a product of cellular respiration.

Unlike photosynthesis, no light energy isrequired for cellular respiration, therefore thisprocess occurs continuously.

Many organisms cannotphotosynthesize. Therefore,they are not able to maketheir own energy-rich sugaror building materials.

These organisms, called consumers,obtain energy and building materials byeating other organisms.

The Consumers

To obtain useable energyfrom food, consumersundergo cellular respiration.

While only producersundergo photosynthesis,both producers andconsumers perform cellularrespiration.

Humans are consumers,obtaining energy by eatingother organisms.

Without photosynthesizingproducers, consumers wouldnot have a source of food.

The Consumers