Recycling Materials (Nutrients)

This is the beginning of Chapter Two of Bare Bones Ecology. New definitions are printed in red and defined here. Words that have been described and defined in Chapter One and the introduction to Bare Bones Ecology are printed in green (as soon as I figure out how to do this). You can download Bare Bones Ecology, introduction and chapter one, from the pdf links that are on the right of this blog, or from

Chapter Two is about materials (the nutrients, the chemical components of all living stuff) and how the living whole earth ecosystem is able to stay alive, in part, by recycling the nutrients that it requires to be alive. (One definition of life is the ability of living things to create the conditions that they require to be alive. For one example, your body can do metabolism.) The recycling of materials through the biosphere is one of the things that binds together all the cells and organisms of all the different levels of organization
of the living earth ecosystem into one whole living unit.

Biosphere = the living earth, the earth ecosystem.
The biggest unit of life is the whole earth ecosystem.

All of life is made of exquisitely organized chemical atoms and molecules. Inorganic molecules are provided by the earth; organic molecules are constructed by the organisms, using atoms and inorganic molecules. That’s why the atoms and inorganic molecules are referred to as nutrients for the entire ecosystem. I prefer to word “materials.” The circulation of materials is one of the ways in which cells and organisms of the same and different levels of organization interact with each other to maintain the balance of materials that their bodies are made of.

If you want to think of a comparison, your body is also a (much smaller) unit of life, and it also requires balance among its parts in order to stay alive. One way your body is able to maintain its biochemical balance (metabolism) is (also) to circulate the materials (nutrients) of food (organic energy) as they enter and leave the body. Organisms like us have circulatory systems to do this function. The biosphere has biogeochemical cycles.

Biogeochemical cycle means biological/geological/chemical cycle of materials (nutrients). It describes the way in which chemical components of life are circulated through the organic (biological) and inorganic (geological) parts of the living ecosystem.

Circulation of materials makes the nutrients available throughout the ecosystem, in a form they can be used again and again. For one example, a carbon atom might be used by a plant to make an organic molecule; then an animal eats the plant and the organic molecule is broken apart in the metabolism of the animal; the same carbon atom is then used to make carbon dioxide; the carbon dioxide is excreted into the air, where it circulates around until a plant takes it in and uses it to make another different organic molecule. This is like the physiology of the ecosystem.

This cycle would not happen without the living earth ecosystem. Life is the ability to create the conditions inside itself that are necessary to maintain life.

As an introduction to biogeochemical cycles (biological/geological/chemical) I could not do better than to quote from the classic textbook, Fundamentals of Ecology, by Eugene Odum. Chapter 4, page 86, Third edition, Princles and Concepts pertaining to biogeochemical cycles. A newer edition is available. I have added the comments in parentheses:

“Of the (more or less 100 elements different kinds of atoms) that are known to occur in nature, between 30 and 40 are known to be required by living organisms. Some elements such as carbon, hydrogen, oxygen and nitrogen are needed in large quantities; others are needed in small or even minute quantities. Whatever the need may be, essential elements (as well as nonessential elements) exhibit definite biogeochemical cycles.

“The essential elements, including all the essential elements of life, tend to circulate in the biosphere in characteristic paths from environment to organisms and back to the environment. These more or less circular paths are known as biogeochemical cycles. The movement of those elements (atoms) and inorganic compounds (inorganic compounds are molecules that are not made in the body of a living organism) that are essential to life can be conveniently designated as nutrient cycling. For each cycle it is also convenient to designate two compartments or pools: (1) the reservoir pool, the large, slow-moving, generally non-biological component, and (2) the exchange or cycling pool, a smaller but more active portion that is exchanging (i.e., moving back and forth) rapidly between organisms and their immediate environment. From the standpoint of the biosphere as a whole biogeochemical cycles fall into two basic groups: (1) gaseous types, in which the reservoir is in the atmosphere or hydrosphere (ocean, lake or pond), and (2) sedimentary types, in which the reservoir is in the earth’s crust.”

We don’t need to describe every cycle in order to appreciate that all of the chemical raw materials of life do recycle in the living earth ecosystem, and they all have different, but interacting cycles. So long as the biosphere is healthy (balanced, sustainable, resilient), all of its different organisms contribute to the biogeochemical cycles that bind the entire system together.