Energy Flows in Ecosystems

Where does all the energy captured by plants go?

SBI4U RHSA

About 1% of the sunlight that reaches Earth is captured by plants for photosynthesis.

By converting light energy to the chemical energy of glucose, plants are able to produce 150-200 billion tonnes of organic material a year.

This net primary productivity or biomass is measured in grams of vegetation per square metre per year (g/m2/a).

ridge.icu.ac.jp/gen-ed/ecosystem-jpgs/world-bioproduction.jpg

From the producer level up through the consumer levels the “Rule of 10” applies. This rule states that only about 10% of the energy consumed is used to build cells or new biomass in the consumer.

The other 90% of the energy consumed is “lost” to cellular respiration, heat, feces, urine or other cell functions. Thus less biomass is produced at every

higher consumer level. The Rule of 10 does not apply to the

biomass of decomposers in an ecosystem.

Rule of 10

http://www.rw.ttu.edu/2302_butler/chapter3.htm

www.biocab.org/Energy_Pyramid.jpg

In most aquatic and terrestial ecosystems pyramids representing numbers of organisms, biomass and energy can be drawn.

Pyramids

There are some interesting exceptions to the standard pyramid shape.

Some aquatic ecosystems have an inverted biomass pyramid because the extremely high reproductive rate of the phytoplankton can support a much larger mass of zooplankton.

A deciduous forest, where there is a large amount of biomass in fewer large trees also gives an unusual shape for a pyramid of number of organisms.

Pyramid Exceptions

ridge.icu.ac.jp/gen-ed/ecosystem-jpgs/flow-of-energy.jpg