Biological Organization: Flow of Energy & Cycles of Matter

Instructor: Matthew Bergstresser

Matthew has a Master of Arts degree in Physics Education. He has taught high school chemistry and physics for 14 years.

Energy is constantly being transformed from one form to another. In this lesson, we will look at how energy flows through an ecosystem. We will also see how matter is cycled in the ecosystem.

Earth's Power Plant

There are electrical power plants located all over the world that provide electricity to homes and businesses. This electricity makes our lives easier, and more comfortable. All living things on Earth need a very special power plant to survive. Can you guess what it is? It's the sun! Without the sun, life on Earth would disappear, and Earth would end up dark, cold, and devoid of life. Let's see how energy and matter are transferred in the ecosystem that all starts with the nuclear reaction in the sun.

Flow of Energy

Before we get into energy and matter transfer in the ecosystem, let's take a look at a smaller system to see how energy is transferred. Imagine a toy car that runs on batteries. The chemical potential energy stored in the batteries is transferred to a motor that turns the wheels. The turning wheels are kinetic energy, which is the energy of movement. After running for awhile, the motor gets hot due to friction because of its moving parts. The energy flowed in one direction, and the heat generated by the motor was lost to the environment. This parallels what happens in the ecosystem.

Two out of the three laws of thermodynamics apply to energy transfer in the ecosystem. Let's look at the first law.

Energy Cannot be Created or Destroyed

We talked about the sun being the power plant for life on Earth. The fusion reaction in its core transforms the energy of the atomic nucleus into heat and light. Less than 10% of that energy is absorbed by plants, and about half of that is used by plants in photosynthesis! Photosynthesis is the special ability of plants to turn light into chemical potential energy (matter). The first law of thermodynamics states that energy cannot be created or destroyed. It changes forms, though. Photosynthesis is an example of this transformation of energy. This leads us to the second law of thermodynamics.

Lost Energy

The second law of thermodynamics states that when energy is transferred, some of it is always lost as heat. Animals eat, move around, reproduce, and generate heat from cellular processes. This heat is lost to the environment. We have all experienced this when we sit on a seat that someone has been sitting on. It is warm. Heat their cells generated left their body and warmed their immediate surroundings. That energy is not recovered to be transformed into another form of energy.

Unidirectional Flow

The flow of energy in the ecosystem is unidirectional, which means that energy only flows in one direction. For example, the heat generated by animals, which is lost, can not be reused by plants to create plant material. In other words, energy can't be recycled.

Energy flows in one direction. Inefficiency, and energy lost as heat is represented by red arrows.

The efficiency of energy transfer and flow depends on a few factors. The first factor is at the primary producer (plants) stage. Everything depends on how efficient plants are at converting sunlight into plant material, which is chemical potential energy. They don't transform all of the light that reaches them into plant matter.

The second factor is how much of that chemical energy is actually used. Not every plant gets eaten!

The third factor is how much of that eaten chemical potential energy is used by the animal for metabolic processes, which are all of the functions done at the cellular level. Some of the food eaten is expelled as waste.

The fourth factor deals with what we have already discussed, losing heat to the surroundings. Let's now discuss how matter is cycled through the ecosystem.

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