Лекция: Biogeochemical Cycles

Of the earth’s 92 naturally occurring elements, only 20 to 30 are constituents of living organisms and thus are cycled through the biosphere. In chemical terms, life can almost be summed up in five words: carbon, oxygen, hydrogen, nitrogen, and phosphorus. These chemicals as elements and compounds make up 97% of the mass of your body and more than 95% of the mass of all living organisms.

The remaining 15 to 25 elements needed in some from for the survival and good health of plants and animals are required only in relatively small, or trace, amounts. The importance of a particular chemical to a living organism varies with the physical and chemical from and location of the chemical. For example, plants obtain most of their carbon in the form of carbon dioxide gas from the atmosphere or water, and most of their nitrogen and phosphorus as nitrate ions and phosphate ions from soil water in which containing these ions are dissolved.

Only a small portion of the earth’s chemicals exist in forms useful to plants and animals. Fortunately, the essentially fixed supply of elements and compounds needed for life is continuously cycled through the air, water, soil, plants, and animals and converted to useful forms in biogeochemical cycles (bio meaning “living”, geo for water, rocks, and soil, and chemical for the matter changing from one form to another). These cycles, driven directly or indirectly by incoming energy from the sun, include the carbon, oxygen, nitrogen, phosphorus, and hydrologic cycles.

Thus a chemical may be part of an organism at one moment and part of its nonliving environment at another moment. This means that one of the oxygen molecules you just inhaled may be one inhaled previously by you, your grandmother, King Tut thousands of years ago, or a dinosaur millions of years ago.

Similarly, some of the carbon atoms in the skin converting your right hand may once have been part of a leaf, a dinosaur hide, or a limestone rock. Without the biogeochemical cycles, the entire world would soon be knee-deep in plant litter, dead animal bodies, animal wastes, and garbage.

Упражнение 9.

Выберите из текста Biogeochemical Cycles 10–15 основных,
с точки зрения смысловой нагрузки, слов (ключевые слова). Определите, к каким частям речи они относятся.

Упражнение 10.

Переведите текст письменно. (Контрольное время – 30 минут)