Carolyn N. Kinder
The biosphere is the relatively thin stratum of the Earth’s surface and upper water layer that contains the total mass of living organisms, which process and recycle the energy and nutrients available from the environment.
The whole Earth is an ecosystem, a system of give and take among plants, animals and their surroundings. As in any system, whatever happens to one part of an ecosystem affects its other parts. Materials are cycled from soil, water and air through the plants and animals and then back to the soil, water and air.
The energy that operates the ecosystem originates in the sun. This solar energy is trapped by green plants in the food they manufacture during the process of photosynthesis. The energy is needed to hold atoms of carbon, hydrogen, oxygen, nitrogen and other elements together in the compounds we call food. As the food is used by the plants, by animals that eat the plants and by animals that eat other animals, energy is released and used. As carbon and other elements are cycled through the plants and animals and back into the soil, water and air, energy dissipates.
An understanding of the biosphere involves the study not only of its constituent organisms but also the cycles by which energy and essential substances are transferred among species and between the biotic and abiotic segments of the environment. Photosynthesis, for example, the first stage in the conversion of solar energy into usable nutrients, operates at maximum efficiency of three (3) per cent. At each stage in the transfer of this energy through the consumption of plants by animals, efficiency declines. In order for an organism to make the most efficient use of the energy it consumes, it must regulate its activity within an environment that supplies the temperature and the amounts of sunlight, water, and essential elements optimal for its species.
As energy flows in a single direction from solar radiation through plants and animals to humans and is dissipated at each successive stage, the chemical elements essential for life cycle through the biotic community. Gaseous elements are generally transferred through the atmosphere or hydrosphere, and the mineral elements such as magnesium, boron, sulfur, calcium, potassium, and phosphorus are absorbed through the soil and transmitted by water to plants and animals. Oxygen, for example, is cycled as an element of water and of mineral compounds, and it is released into the atmosphere in its free form by photosynthesis.
Most important of all, perhaps, is the cycle of water, a substance necessary for all life forms and a principal determinant of the climatic conditions suitable for each species. Water is circulated primarily through evaporation and precipitation and distributed chiefly as a liquid over much of the Earth’s surface, or as atmospheric water vapour. It is absorbed directly by plants and animals in both liquid and gaseous states and is released through respiration, perspiration, elimination, and, in plants, transpiration. Besides its importance as a component of all organisms, it also serves as a medium for the transference of nutrients and assists in the regulation of internal conditions such as body temperature.