MadSci Network: Environment & Ecology

Re: What is energy flow through an ecosystem??

Date: Sat May 13 01:27:12 2000
Posted By: Steven Seefeldt, Staff, Crop protection/weed science, AgResearch
Area of science: Environment & Ecology
ID: 955407062.En

Hi Sarah,

For the answer let's ignore the deep sea hot water vents and just talk 
about above ground ecosystems.  The energy flow is all about food, making 
it and eating it.  For a typical above ground ecosystem the first energy 
source is the sun.  Plants, some bacteria, and algae can use this energy 
(photons of light within a narrow range of wavelengths) plus, water and 
carbon dioxide to make simple sugars (food).  This process is called 
photosynthesis.  The sugars are in turn used to provide energy and building 
blocks to make more complex compounds.  The plants that photosynthesize are 
called producers, everything else is a consumer.  For the plant to grow it 
uses energy from the sun to do it and in a sense you can say a plant 
represents that energy.

A primary consumer is a plant eater (herbivore - cow, bacteria, fungus, 
etc.).  A plant eater grows by using the energy that is stored in the 
compounds of a plant.  There is a certain amount of waste (it takes energy 
to break chemical bonds and make new ones etc.), but there is enough energy 
left over for the organism to survive and grow.  As a rule of thumb, an 
herbivore will gain a kilogram for every 10 kilograms it eats when it is 
young and growing actively.

Secondary consumers eat primary consumers and the energy flow continues 
through them.  Again about 10 kg of gazelle will allow a young lion to grow 
about 1 kg.  You can imagine that when the lion dies, another animal 
(vulture) will come and eat it, again transferring the energy in the 
ecosystem.  You can go crazy trying to figure where all the energy in an 
ecosystem goes.  But what is important is remembering that photosysthesis 
allows organisms to capture the sun's energy and everything else ultimately 
gets its energy (food) from eating the plant or eating something that ate 
the plant.

If the plants are aquatic in a bog, enventually they can end up as coal.  
If we burn that coal we will get back some of the sun's energy that has 
been in long term storage.

Hope this little bit has been helpful.  It's a big and interesting field.  
I looked at a textbook - Biological Science, An ecological appoach (BSCS 
Green Version) 6th edition. Kendall/Hunt publishing co.  Iowa. for 
inspiration.  It's the best biological science textbook I have ever seen 
and I recommend it highly.


Steve Seefeldt

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