Essential idea: Ecosystems require a continuous supply of energy to fuel life processes and to replace energy lost as heat.

The image above shows an eruption on the surface of the sun. Without a constant stream of solar radiation much of the life on Earth would not be possible. The sun's energy is the source of energy in the vast majority of the Earth's ecosystems.

4.2 Energy flow

https://svs.gsfc.nasa.gov/vis/a010000/a012000/a012034/Combined.00_29_05_33.Still002.jpg

By Chris Paine

http://www.bioknowledgy.info/

Understandings, Applications and Skills

Statement Guidance4.2.U1 Most ecosystems rely on a supply of

energy from sunlight.

4.2.U2 Light energy is converted to chemical energy in carbon compounds by photosynthesis.

4.2.U3 Chemical energy in carbon compounds flows through food chains by means of feeding.

Pyramids of number and biomass are not required. Students should be clear that biomass in terrestrial ecosystems diminishes with energy along food chains due to loss of carbon dioxide, water and other waste products, such as urea.

4.2.U4 Energy released from carbon compounds by respiration is used in living organisms and converted to heat.

4.2.U5 Living organisms cannot convert heat to other forms of energy.

4.2.U6 Heat is lost from ecosystems.

4.2.U7 Energy losses between trophic levels restrict the length of food chains and the biomass of higher trophic levels.

The distinction between energy flow in ecosystems and cycling of inorganic nutrients should be stressed. Students should understand that there is a continuous but variable supply of energy in the form of sunlight but that the supply of nutrients in an ecosystem is finite and limited.

4.2.S1 Quantitative representations of energy flow using pyramids of energy.

Pyramids of energy should be drawn to scale and should be stepped, not triangular. The terms producer, first consumer and second consumer and so on should be used, rather than first trophic level, second trophic level and so on.

http://commons.wikimedia.org/wiki/File:Plagiomnium_affine_laminazellen.jpeg

4.2.U1 Most ecosystems rely on a supply of energy from sunlight.

Most ecosystems rely on light energy received from the sun.

https://commons.wikimedia.org/wiki/File:Blacksmoker_in_Atlantic_Ocean.jpg

In a very few ecosystems the producers are chemoautotrophs, e.g. volcanic vents on the ocean floor, which use energy from chemical processes.

All plants and some prokaryotes are photoautotrophs. They use pigments, such as chlorophyll, to trap light energy, which is into converted into chemical energy in carbon compounds.

Review: 4.3.U1 Autotrophs convert carbon dioxide into carbohydrates and other carbon compounds. AND 4.2.U2 Light energy is converted to chemical energy in carbon compounds by photosynthesis.

http://commons.wikimedia.org/wiki/File:Plagiomnium_affine_laminazellen.jpeghttp://www.earthtimes.org/newsimage/photosynthesis-dream-renewable-energy_1_02842012.jpg

n.b. Although most autotrophs fix carbon by photosynthesis. A few are Chemoautotrophs and fix carbon by utilising the energy in the bonds of inorganic compounds such as hydrogen sulfide.

All autotrophs however convert carbon dioxide (from the atmosphere or dissolved in water) or into organic compounds.

Plant initially synthesis sugars (e.g. glucose) which are then converted into other organic compounds such as:• complex carbohydrates e.g.

starch, cellulose• lipids• amino acids

The light energy from the sun is used to synthesis carbohydrates. The light energy is transferred into bonds (chemical energy) between the atoms in a carbohydrate molecule.

4.2.U3 Chemical energy in carbon compounds flows through food chains by means of feeding.

http://www.slideshare.net/gurustip/communities-and-ecosystems

4.2.U4 Energy released from carbon compounds by respiration is used in living organisms and converted to heat.

Energy stored in organic molecules (primarily carbohydrates and lipids) can be transferred by cell respiration to ATP.

Edited from: http://www.ib.bioninja.com.au/_Media/energy-forms_med.jpeg

No energy transfer is 100% efficient: ‘wasted’ heat (thermal) energy is produced too.

Other inefficiencies in the transfer of energy between and within organisms include:• Toxic waste organic

molecules are excreted• Some ingested material is

not absorbed and ends up being egested

• Some parts of an organism remain uneaten, e.g. woody fibres from plants and the bones of animals.

ATP in turn is used by cells to support their metabolism:• Building and breaking down molecules

(anabolism and catabolism)• Homeostasis• Growth

4.2.U5 Living organisms cannot convert heat to other forms of energy. AND 4.2.U6 Heat is lost from ecosystems.

Useful energy transfers from chemical energy:• kinetic energy, e.g. muscular contractions• electrical energy, e.g. nerve impulses• light energy, e.g. bioluminescence• chemical energy, e.g. anabolism• sound energy, e.g. communication• Heat energy, e.g. body temperature in

endotherms

No energy transfer is 100% efficient: ‘wasted’ heat (thermal) energy is produced too.

Unlike light and chemical energy organisms cannot convert heat energy into forms useful to the organism.

Thermal energy released from the organism dissipates into the ecosystem and is eventually lost from it.

Therefore ecosystems require a continuous supply of energy (e.g. sunlight) to persist.

http://www.sciencemag.org/sites/default/files/styles/article_main_large/public/images/sn-hummingbirds_1.jpg?itok=h9E5jae0

4.2.U7 Energy losses between trophic levels restrict the length of food chains and the biomass of higher trophic levels.

n.b. organisms vary in their efficiency of energy transfer; it maybe as high as 20% or as low as 5%.

http://www.slideshare.net/gurustip/communities-and-ecosystems

4.2.S1 Quantitative representations of energy flow using pyramids of energy.

Pyramids of energy always get smaller at higher trophic levels due to the loss of energy.

The bottom level will always represent the producers, with subsequent levels representing consumers (primary, secondary, etc.)

Bars should be roughly drawn to scale, e.g. secondary consumers should be 1/10th the width of primary consumers.

Drawing pyramids of energy

1

2

3

Image from http://www.slideshare.net/gurustip/communities-and-ecosystems

4.2.U7 Energy losses between trophic levels restrict the length of food chains and the biomass of higher trophic levels.

Chemical energy is held in molecular bonds. Therefore as energy is lost between trophic levels it is natural for biomass* to be lost too.

Biomass therefore is often used to indirectly measure energy transfers.

*Biomass is usually measured as the total dry mass of organisms#Competing hypotheses assert that ecosystem size is a more important factor than productivity

As the trophic level increases the is biomass and energy available decreases

Energy losses between trophic levels limit the length of food chains.

Higher trophic levels are often less efficient as more energy is spent on foraging more mobile prey

Eventually the energy required to forage exceeds the energy gained from foraging, making the trophic level unviable#

n.b. Most food chains contain between three and six organisms.

Image from http://www.slideshare.net/gurustip/communities-and-ecosystems

Explain the the flow of nutrients and energy through ecosystems (8 marks)

http://www.slideshare.net/gurustip/communities-and-ecosystems

Explain the the flow of nutrients and energy through ecosystems

energy flows linearly, nutrients are cycled

(8 marks)

Bibliography / Acknowledgments