Transcript Energy Transfer through organisms

Energy Transfer through
organisms
Energy flows through an ecosystem, being
transferred from one organism to the next.
Energy flows in one direction, obeying the law
of conservation of energy.
Energy cannot be created or destroyed,
only changed from one form to another.
When energy is converted from one form to another, some is always lost as heat. This
inefficiency of transfer limits the number of organisms found in any food chain.
Obtaining energy
Energy availability in photoautotrophs
Primary production
Net primary productivity (NPP) is a good way to compare
different ecosystems. The availability of light, water and
nutrients are different around the world and therefore the
productivity of the world’s ecosystems also varies greatly.
desert ecosystem
NPP =
260 kJm-2 year-1
tropical rainforest
ecosystem NPP =
400,000 kJm-2 year-1
Ordering NPP of ecosystems
The net primary productivity represents the potential food
available to consumers in the ecosystem. This energy can
be transferred to the next trophic level in several ways:

The organism is consumed
by a primary, secondary or
tertiary consumer.

Death, production of urine and
feces and loss of organic tissue
(e.g. fruit fall, hair loss) allows the
energy from the organism to be
passed on to decomposers.
The rate at which energy is used to make new organic
molecules within heterotrophs is known as secondary
production.
As with the transfer of energy from the sun to autotrophs,
the transfer of energy from one organism to another is
inefficient. The efficiency of chemical potential energy
transferred between trophic levels can be measured.
efficiency =
energy available after the transfer
× 100
energy available before the transfer
The energy available is usually measured in kilojoules per
square meter per year (kJm-2 year-1).
A large percentage of the energy is lost between trophic levels.
This is as a result of the following:

Some of the organism cannot
be eaten, e.g. bones, fur, etc.

Once eaten, some of the
organism cannot be digested.

Energy is lost in excretory
materials, such as urine.

Energy is lost in the form of heat
from respiration and body heat.
Comparing trophic efficiencies
Efficiency of transfers in a food chain
Energy transfer: true or false?