Biological Productivity and Energy Flow

 Central African Republic: Violence Increases Hunger Risk, U.N. Warns  ess/world-hunger-the-problem-left-behind- economic-view.html ess/world-hunger-the-problem-left-behind- economic-view.html  ess/energy-environment/a-200-year-old- forecast-for-food-scarcity-may-yet-come- true.html ess/energy-environment/a-200-year-old- forecast-for-food-scarcity-may-yet-come- true.html

 1. How many bushels of wheat can a farmer produce in a field in a year?  2. What is the upper limit of food that can be produced for all the people on Earth?  What is the limit on the number of whales in the ocean?  What is the maximum production that we can expect of forests?  The ultimate limit on production of organic matter is energy flow.

 Total amount of organic matter = biomass  Measured in amount per unit area(g/m 2 )  Increased through growth  Change over time = net production  The capture of usable energy to produce organic compounds where that energy is stored = biological production

 1. Primary – autotrophs a. photo b. chemo 2. Secondary – heterotrophs - Organic matter may be used for: a. Moving b. Making new compounds c. Growing d. Reproducing e. Storage - Energy is made available through respiration

 Gross Primary Production, GPP, is the total amount of CO 2 that is fixed by the plant in photosynthesis.  Respiration, R, is the amount of CO 2 that is lost from an organism or system from metabolic activity.  Net Primary Production, NPP, is the net amount of primary production after the costs of plant respiration are included. Therefore, NPP = GPP - R

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 All life requires energy.  – The ability to do work  Ecosystem energy flow - the movement of energy through an ecosystem from the abiotic environment through a series of organisms (biotic) and back to the abiotic part of the environment.

 Energy enters an ecosystem by two pathways.  – 1. Energy fixed by organisms (photosynthesis)  – 2. Transfer of heat energy by air, water, soil, and warm living things.

 First law = Law of conservation of energy  – In any physical or chemical change, energy is neither created nor destroyed but merely changed from one form to another.  Second law = Law of Entropy – Energy is always increasing level of chaos (becoming less useful).

 As energy flows through a food web, it is degraded, and less and less is useable.  Energy efficiency- the ratio of output to input – The amount of useful work obtained from some amount of available energy

 Trophic-level efficiency- the ratio of production of one trophic level to the production of the next trophic level.  – Never very high  – 1-3% in natural ecosystems  – 10% may be maximum efficiency!  – 90% of all energy lost as heat