BIOSPHERE

1. Biosphere is arelatively 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 biosphere is postulated to have evolved beginning through a process of biopoesis at least 3,5 billion years.

2. The primary source of energy for all life is solar radiation, and the minerals and other substances converted and used by organisms are drawn from the geosphere, or nonliving world, which consists of the atmosphere (the air), the hydrosphere (the water) and the lithosphere (rocks and soil of the terrestrial surface). A relatively recent conception of the Earth views all of these layers, both biotic (living) and abiotic (nonliving or geophysical), as components of an integral complex of interdependent systems known as the ecosphere.

3. The organisms of the biosphere range from the simplest unicellular microbes to humans. All life forms can be classified according to their function. Green plants are considered productive organisms because their photosynthetic conversion of water and carbon dioxide into carbohydrates supplies the basic nutritive substances for life. A second category consists of the organisms that consume and convert the energy stored in plants, including all species of animals, and a third category consists of microorganisms that decompose organic detritus into simpler forms that can be used again in the productive processes of plant growth. Groups of species in a defined region form biotic communities which, together with the nonliving components of their environment, constitute an ecosystem.

4. An understanding of the biosphere entails the study not only of its constituent organisms but also of 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 a maximum efficiency of 3 percent. 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.

5. 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 flow through the biogeochemical cycle from the nonliving environment through the biotic community and eventually return to their former state through organic decay. 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 is released into the atmosphere in its free form by photosynthesis.

6. 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 (e.g., ocean currents and river runoff) 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, 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.

Поиск по сайту: