Energy Flow Through an Ecosystem

When sunlight hits an object it is either reflected or absorbed.

Reflected Energy

            ○          About 30% of solar energy is reflected by water, land, clouds, plants, buildings, etc.

            ○          reflected energy does not heat objects up.

Absorbed Energy

            ○          About 70% of solar energy is absorbed by water, land, clouds, plants, buildings, etc.

            ○          Energy that is absorbed heats objects up.

            ○          Dry objects heat up faster than wet objects.

                        -          Sun shining on a beach makes the dry sand hot to the touch.

                        -          Sun shining on wet sand or grass does not.

                        -          This is because the water in the grass or wet sand absorbs the solar energy so that the item does not heat up.

            ○          Transpiration

                        -          When plants absorb solar energy, the heat is used to evaporate water from the leaves. The water is lost through tiny openings in the leaf.

            ○          Less than 1% is used by living things.

•          Without a constant source of energy, living systems cannot function.

•          Sunlight is the main source of energy for life on Earth. (Some organisms can obtain energy from chemicals rather than using sunlight)

•          All organisms need a source of energy (or food).

•          Organisms can be put in categories depending on how they get energy (or food)

Producers

•          Plants, algae, and some bacteria capture energy from the sun to make food.

•          Some of the solar energy absorbed is trapped by chlorophyll and used to make sugar. This process is called photosynthesis.

•          Photosynthesis also uses carbon dioxide and produces oxygen. Without producers, there would be no oxygen for us to breathe.

•          The equation is: carbon dioxide + water ➞ sugar + oxygen

•          These organisms are also called autotrophs.

•          They produce food for all other organisms in the ecosystem.

Consumers

•          Animals, fungi, and some bacteria cannot make their own food using photosynthesis.

•          To get food they must eat other organisms.

•          They are also called heterotrophs.

•          When a consumer eats a plant, it gets energy from the sugar the plant made. This process is called cellular respiration.

•          The equation is: sugar + oxygen ➞ carbon dioxide + water

•          Notice that it is the reverse of photosynthesis.

•          There are five different kinds of heterotrophs:

            •          Herbivores eat producers.

            •          Carnivores eat other consumers.

            •                      Predators eat live prey.

            •                      Scavengers eat something which is already dead.

            •          Omnivores eat both producers and consumers.

            •          Detritivores eat dead plants and animals.

            •          Decomposers break down organic matter so that it can be recycled back into the ecosystem.

Food Chains

•          Energy flows through an ecosystem in one direction, from the sun to autotrophs, and then to heterotrophs.

•          The energy captured by autotrophs is passed through an ecosystem along a food chain.

•          A food chain is a series of steps showing the flow of energy from producers to consumers.

Building a food chain

1.         1^st step is always a producer because they can produce food for all other organisms.

2.         2^nd step is always a herbivore (or omnivore) because they must eat a producer. This organism is called a primary consumer.

3.         3^rd step is always a carnivore (or omnivore) because they must eat a consumer. This organism is called a secondary consumer.

4.         The last organism in the chain is called the top carnivore. It is not prey to any other organism

5.         Each level of the food chain is called a trophic level

Food Webs

•          In most ecosystems, feeding relationships are much more complex than simple chains.

•          Organisms usually have several choices of what they will eat and they might be eaten by several different organisms.

•          A food web links all the food chains in the ecosystem together.

•          The more complex the food web the more stable the ecosystem. This is because if one organism is removed, others still have other options for food.

Ecological Pyramids

•          Biomass is the total of all organic matter at any level of a food chain.

•          In natural ecosystems, the plant biomass is greater than the herbivore biomass which is greater than the carnivore biomass.

•          An ecological pyramid shows the relative amounts of energy or matter contained within each trophic level in a food chain.

•          Most energy at each level is used by organisms in that level to grow, reproduce, and move around.

•          Some of the energy is lost as heat.

•          Only about 10% is passed on to the next level.

•          This means that the more levels in a food chain, the less energy reaches the top so fewer organisms can be at the top of the chain.

•          In countries like China and India, people have to eat more plants and less meat because they cannot produce enough meat.

•          Part of the solution to world hunger is for all of us to eat more plants and less meat.

Interfering with Pyramids

Several things can interfere with ecological pyramids.

•          Seasons

            •          In winter there are fewer producers so there are fewer consumers.

            •          Every level of the pyramid gets smaller.

•          Natural events

            •          Fire, earthquakes, and floods can destroy producers. This means fewer consumers.

            •          When the producers recover, the other levels will as well.

•          Human events

            •          Hunting and fishing

                        •          Cod, halibut, and salmon are being wiped out because of fishing technology and dams.

                        •          Other species in the food chain are also affected.

            •          Pesticides

                        •          The use of chemical pesticides eliminates good and bad insects so that the whole food chain is affected.