E5 Summary

Stage 2 Biology – Ecosystems Notes

 

E5. More energy flows through a community than is captured in living mass

 

·         Produces are the starting point for all organisms in terms of energy

o   Photosynthesis traps the sun’s energy and stores it as chemical energy

o   Energy is trapped in the bonds of organic molecules (ie. glucose)

·         A community consists of various trophic levels, and each level obtains energy requirements from the level below

·         Earth receives more energy in the form of sunlight than can be trapped by producers

o   Most is absorbed or reflected by the Earth’s surface or atmosphere

o   About 1% of the energy striking the Earth is trapped and converted to chemical energy

o   Plants use a considerable amount they trap in maintaining life process

o   Therefore there is much less energy available to the next trophic level

·         Energy conversion is not totally efficient

o   Heat energy will be produced during the reaction, which is ‘lost’ to the environment and not passed on to the next trophic level

·         Example:

o   A gum tree traps a percentage of light that hits its leaves through photosynthesis

o   Some energy is used by the tree to build new tissue and maintain life processes

o   Only a small percentage (10%) is available to the insects that eat the plant

o   Organisms do not digest and absorb all food material they eat

o   Approximately 90% drop in energy at each trophic level

o   Most energy is lost as heat into the atmosphere

·         Light intensity determines productivity of a community

o   In the open ocean, most photosynthesis occurs at the surface – phytoplankton are the main autotrophs – productivity is 3-6 times less than in a typical forest

·         Chemoautotrophs

o   Use energy from organic molecules to help them convert inorganic materials into organic molecules

o   Simple prokaryotic bacteria

o   Biomass production is small

o   Example is bacteria living near hydrothermal vents – obtained energy from sulphur compounds by converting carbon dioxide from sea water into the organic compounds they need

·         Atmosphere and global warming

o   A largely transparent layer

o   Allows solar radiation from the sun to be transmitted through it

o   Some gases (carbon dioxide and methane) reflect heat back into the atmosphere

o   These greenhouse gases are essential to maintain the warm, stable environment that is essential to sustain life

o   Stability of the temperature is due to the fact that input and output of energy on Earth are almost equal

o   Concern about global warming – gradual increase in temperature

o   Human actions – industrialisation, fossil fuel burning, deforestation = higher atmospheric concentrations of carbon dioxide and other gases that trap heat

o   Long term effects – evaporation from the ocean, sea level rises, melting of ice caps