Energy Transfers

How do I use the Energy Transfer Formula?

Large amounts of energy are always lost between each level of the food chain, called trophic levels. This is because of the second law of thermodynamics. This states that whenever energy is converted from one form to another, there is an increase in entropy (disorder) in the system. In the context of the food chain, this means that a great deal of energy is lost in the form of heat when organisms are consumed.

The efficiency of energy transferred between two trophic levels is called the TLTE. This stands for 'trophic level transfer efficiency' and is determined by the following energy transfer formula:

\[TLTE = \frac{\text{production at present trophic level}}{\text{production at previous trophic level}} \cdot 100\]

As an example, if the energy of grass is stated at 5000 kcal, and the cow which eats the grass received 400 kcal during the energy transfer, the calculation would be as follows:

\[\frac{400 \space Kcal}{5000 \space Kcal} = 8\% \space TLTE\]

Another equation that you need to know is the net production efficiency (NPE). The net production efficiency is used to calculate how efficiently organisms from a trophic level turn the energy they consume into biomass. The formula for NPE is:

\[NPE = \frac{\text{net consumer productivity}}{\text{assimilation}} \cdot 100\]

Net production productivity, or NPP, refers to the amount of energy available to organisms on the next trophic level. Assimilation refers to the biomass of the current trophic level after some energy is lost due to incomplete ingestion of food, waste, and respiration. You can read more about this in energy flow in ecosystems.

How do you show energy transfer on a diagram?

You can display different types of energy transfer in different ways. However, we usually use the diagram below when discussing energy transfer within an ecosystem.

Fig. 1 - The flow of energy in a food chain

This diagram shows the flow of energy of a food chain. As you will see, the energy decreases with each trophic level. The total energy accumulated by the primary producers was shown to be 41,620 kcal /m²/yr.

Since all living things use energy for biological functions, such as respiration, we often pay attention to an ecosystem's net primary productivity (NPP).

In this diagram, 26,374 of the 41,620 kcal/yr was used for respiration or lost as heat, leaving 15,235 kcal/yr of energy for the primary consumers.

What are the different types of energy transfer?

Energy is acquired and transferred through an ecosystem in three different ways: photosynthesis, chemosynthesis, and consumption.

Types of Energy Transfers: Photosynthesis

This is performed by photoautotrophs, such as plants, algae, and photosynthetic bacteria. Photosynthesis allows these organisms to act as the energy source for most of the world's ecosystems. Photosynthesis involves harnessing the sun's energy and converting it into chemical energy in the form of a molecule called ATP (adenosine triphosphate). ATP is then used to fuel the synthesis of a range of biomolecules, including glucose.

Types of Energy Transfers: Chemosynthesis

This is performed by chemoautotrophs, which are typically bacteria that reside in ecosystems that are cut off from sunlight, such as within dark caves or hydrothermal vents on the ocean floor. Chemoautotrophs use chemical compounds, such as hydrogen sulphide, as a source of energy. This allows them to fuel the reactions that create complex biomolecules, including glucose. This creates energy for the rest of the ecosystem.

An example of energy transfer via chemosynthesis would be the process by which specialized bacteria in hydrothermal vents use hydrogen sulphide as a source of energy.

Types of Energy Transfers: Consumption

Consumption is performed by heterotrophs, which function as consumers in the food chain. Heterotrophs get energy in the form of organic carbon. This is done through heterotrophs consuming autotrophs or other heterotrophs. They then break down this organic carbon, which is usually consumed in the form of complex compounds, into smaller, simpler compounds. This releases energy since they are oxidizing carbon and hydrogen and transforming them into carbon dioxide and water. This is achieved via a process called respiration. Studying respiration, you will learn more about various stages of respiration, such as glycolysis and the Krebs cycle.