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бодный кислород, океанические течения, клеточное дыхание, внешний
слой, постоянная переработка, поддерживать баланс элементов.
8. Read the text and answer the questions.
1. Why is the biosphere described sometimes as «the fourth envelope»?
2. What elements does the biosphere contain?
3. How is light converted into glucose and other sugar molecules?
4. What determines the specific composition of the Earth's atmosphere?
5. How important are the oceans for water cycling?
BIOSPHERE
For modern ecologists, ecology can be studied at several levels: popula-
tion level (individuals of the same species), biocoenosis level (or community
of species), ecosystem level, and biosphere level.
The outer layer of the planet Earth can be divided into several com-
partments: the hydrosphere (or sphere of water), the lithosphere (or sphere
of soils and rocks), and the atmosphere (or sphere of the air). The biosphere
(or sphere of life), sometimes described as «the fourth envelope», is all living
matter on the planet or that portion of the planet occupied by life. It reaches
well into the other three spheres, although there are no permanent inhabi-
tants of the atmosphere. Relative to the volume of the Earth, the biosphere is
only the very thin surface layer which extends from 11,000 meters below sea
level to 15,000 meters above.
The biosphere contains great quantities of elements such as carbon, ni-
trogen and oxygen. Other elements, such as phosphorus, calcium, and potas-
sium, are also essential to life, yet are present in smaller amounts. At the eco-
system and biosphere levels, there is a continual recycling of all these ele-
ments, which alternate between the mineral and organic states.
The functioning of the ecosystem is based on the input of solar energy.
Plants and photosynthetic microorganisms convert light into chemical energy
by the process of photosynthesis, which creates glucose (a simple sugar) and
releases free oxygen. Glucose thus becomes the secondary energy source
which drives the ecosystem. Some of this glucose is used directly by other
organisms for energy. Other sugar molecules can be converted to other mole-
cules such as amino acids. Plants use some of this sugar, concentrated in nec-
tar to attract pollinators to help them in reproduction.
Cellular respiration is the process by which organisms (like mam-
mals) break the glucose back down into its constituents, water and carbon
dioxide, thus regaining the stored energy of the sun.
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