Energy transfer between trophic Energy transfer between trophic levelslevels

How much of the Sun’s energy is How much of the Sun’s energy is actuallyactually converted to organic matter? converted to organic matter?

Why?Why?

• 1-3%1-3%• 90+% reflected back into space by dust and clouds90+% reflected back into space by dust and clouds• Some wavelengths of light cannot be absorbed by Some wavelengths of light cannot be absorbed by

plantsplants• Light might not fall on a chlorophyll molecule.Light might not fall on a chlorophyll molecule.• Other limiting factors restrict the rate of Other limiting factors restrict the rate of

photosynthesis such as CO2 concentration and photosynthesis such as CO2 concentration and temperature.temperature.

What are gross and net What are gross and net production?production?

• Gross production is the total amount of energy Gross production is the total amount of energy converted into organic matter.converted into organic matter.

• 20-50% used in respiration.20-50% used in respiration.• Net production is the energy remaining after Net production is the energy remaining after

respiration.respiration.• Net Production = Gross Production – Respiratory Net Production = Gross Production – Respiratory

LossesLosses

Why is the percentage of energy Why is the percentage of energy transfer between trophic levels so low?transfer between trophic levels so low?

• Not all the organism is consumed.Not all the organism is consumed.• Not all parts are digestible so they are Not all parts are digestible so they are

excreted.excreted.• Some energy is lost in excretory substances.Some energy is lost in excretory substances.• Considerable heat is lost by respiration.Considerable heat is lost by respiration.

What can be explained by the What can be explained by the inefficiency of energy transfer between inefficiency of energy transfer between

trophic levels?trophic levels?

• The number of trophic levels being limited to The number of trophic levels being limited to 4 or 5, as there is insufficient energy to 4 or 5, as there is insufficient energy to support a breeding population at this stage.support a breeding population at this stage.

• Biomass decreases at higher trophic levels.Biomass decreases at higher trophic levels.• Less energy is stored at each trophic level.Less energy is stored at each trophic level.

Calculating efficiency of energy Calculating efficiency of energy transfers (kJ/m²/year) transfers (kJ/m²/year)

(Energy available after transfer ÷(Energy available after transfer ÷ Energy Energy available before transfer) x 100available before transfer) x 100

GlossaryGlossary• Trophic level – the position of an organism in a food Trophic level – the position of an organism in a food

chainchain• Gross Production – total amount of the Sun’s Gross Production – total amount of the Sun’s

energy converted to organic matterenergy converted to organic matter• Net Production – organic matter available after Net Production – organic matter available after

respiratory/excretory lossesrespiratory/excretory losses• Biomass – total mass of living material in a specific Biomass – total mass of living material in a specific

area at a given time.area at a given time.• Energy efficiency – the percentage of energy used Energy efficiency – the percentage of energy used

after the transfer for growth and other processes after the transfer for growth and other processes rather than wasted.rather than wasted.