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Energy in ecosystems:
Organisms that produce energy containing organic molecules, using an external energy source, to
make inorganic molecules react together are known as producers. This is usually carried out via
photosynthesis. The entire community relies on the producers. All of the remaining organisms are
known as consumers.
Organisms that feed directly on producers are primary consumers and are usually herbivores.
Animals that eat primary consumers are secondary consumers. Above them are tertiary
consumers and so on. This sequence forms a food chain. A food chain is the sequence in which
energy is passed from one organism to another, in the form of chemical energy in organic
Each step in the food chain is known as a trophic level. Organisms that feed on dead bodies and
waste matter from all trophic levels are known as decomposers.
Not all of the energy from the sun is used by leaves. Some solar energy is reflected, some
passes straight through the leaves, some is the wrong wavelength and some is converted into
heat during photosynthesis. Around 90% of energy is lost through trophic levels.
Energy is also lost through food as some parts of it, bones & roots, are not eaten so energy is
not taken in and some parts of food are indigestible and so pass straight through the organism.
The rate at which a plant produces organic materials through photosynthesis is its gross primary
However a lot of this energy is lost to the environment when organisms use energy produced
from respiration for movement or body heat. This is called respiratory loss.
The net gain of dry mass, or biomass, stored in the plant after respiration is known as the net
primary productivity (NPP).
NPP = GPP respiration or net productivity = gross productivity respiratory loss.
Energy in ecosystems