Building Bodies

How are the bodies of living things built?

Building a living body requires a constant supply of matter from external sources. Once that matter is taken in, it must be processed so that it can be used by the organism. Stated simply, as matter is processed, molecules are broken down and their atoms are rearranged to form different molecules. These new molecules, alone or combined, serve to build and sustain the organism that synthesized them.

In this forest, producers take in water and carbon dioxide

There are a few notable differences in how bodies are built in producers, consumers, and decomposers.

Producers represent the bridge for matter from the nonliving to the living world. Plants are a good example. Plants take in carbon dioxide gas from the air and water from the soil. From these inorganic molecules, they synthesize the organic molecule sugar and release oxygen gas as a by-product. Sugar plays two roles. Sugar is the food that supplies energy to the plant. It is also the raw material from which all the other organic molecules that compose a plant are built. The other elements that are required to sustain a plant’s life, such as nitrogen and phosphorus, are obtained from the soil.

Consumers obtain matter to build their bodies from food. All of the classes of organic molecules are found intact in a consumer’s food. Ingestion brings this matter in and digestion breaks it down into the molecular subunits described earlier (i.e., sugars, amino acids, fatty acids). These subunits are then absorbed into cells, where cell processes rebuild them into the organic molecules that compose the consumer. Vitamins and minerals are also a part of a consumer’s food. Vitamins are organic molecules formed by living things. Minerals are inorganic and originate from the physical environment. Both are critical to life processes.

Decomposers also build their bodies from food. They are considered to be a special class of consumers that are distinguished from others because their food consists of dead bodies as well as the solid and liquid wastes from consumers. As part of building their bodies, the decomposers release inorganic molecules as waste products. In this way, decomposers return matter in the living world to the nonliving world. While considered wastes for the decomposers, however, this matter is what plants take in as nutrients. Decomposers thus represent a critical link in material cycles.

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