Energy Transfer through organisms

Energy flows through an ecosystem, being transferred from one organism to the next. 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. Energy flows in one direction, obeying the law of conservation of energy.

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 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 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 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. The energy available is usually measured in kilojoules per square meter per year (kJm -2 year -1 ). efficiency energy available after the transfer energy available before the transfer = × 100

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?