Energy & Matter in Natural & Engineered Systems

Instructor: Tandi Carignan

Tandi Carignan is a 15 year veteran teaching science at the high school and advanced placement level and was named 2006 Teacher of the Year in her district. Her Masters Degree from Eastern Connecticut State University is in Secondary Science Education and a BS from the University of Connecticut in Environmental Marine Biology. She holds a Connecticut teacher certification with Endorsements in Biology.

All ecosystems, natural and engineered, require a constant supply of energy and matter. Explore how energy is accessed and then lost to the environment while matter continually is reused and recycled. Updated: 05/06/2022

Energy Flow

A phrase common in biology is ''energy flows but matter cycles''. This phrase refers to the entrance and eventual dissipation of energy while matter is recycled and reused in both natural and engineered environmental systems.

The energy for life on Earth originates primarily from the sun. Plants absorb this energy during photosynthesis which is then used for the plant to grow and reproduce. Approximately 90% of the energy absorbed from the sun is utilized by the plant and 10% is stored. When an herbivore eats the plant, it has access to that 10% of energy, which it uses to grow, move around, and reproduce. The energy they store is then transferred to carnivores (meat eaters). Since the energy transfer is directional (the plant doesn't get energy back from the herbivores) this movement is referred to as energy flow.

At each level there is a decrease in energy due to use and loss from the food chain to the environment. Trophic efficiency refers to how much energy is available at each trophic (feeding) level. Trophic efficiency is normally approximately 10% transfer with 90% used or lost to the environment, so the lower trophic levels (plants) have access to more energy than any of the herbivores or carnivores.

Matter Cycles

Matter on the other hand, exists in a cycle rather than a flow. The majority of living creatures are made with the elements carbon, hydrogen, oxygen, and nitrogen. These elements are essential to the life of all creatures as well as their ability to reproduce. They are also the main molecules that make up the basic components of life: the carbohydrates, lipids, nucleic acids and proteins. Unlike energy that is lost to the food chain at each feeding level, the elements of life are continually cycled through the environment to be constantly reused and recycled.

Basics of the Carbon Cycle

Carbon molecules in the atmosphere are able to enter the food chain through photosynthesis. Plants take in carbon (in the form of carbon dioxide), and store it primarily as sugars in their fruits, stems, and leaves.

As animals eat plants, they are able to take in these carbon molecules during respiration and release carbon dioxide back into the environment. In this manner, carbon circles from atmosphere to plants to animals and back to the atmosphere.

Hydrogen, Oxygen, and Nitrogen Cycles

Hydrogen and oxygen combine as water to create the water cycle, which enters and exits the atmosphere through evaporation and precipitation. Biological reactions require water to function.

Nitrogen, like carbon, hydrogen and oxygen, exists freely in the atmosphere. Nitrogen is necessary for the creation of DNA (the instructional molecules of life) as well as proteins (the molecules that allow daily functions). Unfortunately, humans and other animals cannot access atmospheric nitrogen directly, but rather rely on nitrogen-fixing bacteria that extract the nitrogen out of the atmosphere and embed it in the roots of legumes, allowing nitrogen to enter the food chain. Nitrogen is released back to the atmosphere through bacterial transfer as well. The ability of bacteria to cycle nitrogen from the atmosphere to the food chain and back allows for the DNA and proteins that all living creatures require.

Engineered Systems

Natural systems exist without human intervention, while engineered systems are created by humans. In these artificial (engineered) systems, humans supply the necessary sources of energy and matter. For example, indoor gardens require artificial light to mimic energy from natural sunlight. Grow lights are used to provide the correct frequencies of light for optimal plant growth.

Engineered systems must also provide the matter (carbon, hydrogen, oxygen, nitrogen) required for life, often starting with the plant portions of the ecosystem. Since most engineered systems will have access to air, acquiring the carbon necessary for growth will already be a part of the system. Water sources must be included and circulated to allow the plants to obtain hydrogen and oxygen.

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