energy, which is utilized in the chemical reactions leading to the synthesis of
carbohydrates. The biochemistry is extremely complex and is surveyed in the
specialized literature. The general equation is represented as follows:
As a result of photosynthesis molecular oxygen (O₂) is released into
the atmosphere raising gradually its content up to 21% in our day.
The accumulation of oxygen in the atmosphere has become the
prerequisite for the augmentation of the variety of living forms —
photosynthesizing bacteria, blue-green algae, fungi, plants and animals.
Only the first “earth inhabitans” — the anaerobic bacteria — have proved
suppressed by the increase of oxygen. Some of them have been wiped out
forever, some have adapted themselves as facultative anaerobes, and
others have found their ecological niche and have continued up to the
present day so as to “testify” to the far-off past when life has emerged and
started to develop.
The primary products (mainly glucose), formed in the light stage of
photosynthesis as result of a number of successive redox processes during
the dark stage, are converted into different sugar derivatives with the
release of energy used for meeting the energy needs of the cells and for
the synthesis of organic compounds, and in the end they are degraded to
CO₂ and H₂O. This problem can be generally presented in the following
manner:
Upon comparison of the two summed up equations of the process of
photosynthesis (assimilation) and the one of respiration (dissimilation) we
can be easily convinced that the law of preservation and conversion of
energy is strictly observed. This shows that living matter exists and
develops in the framework of the general laws for preservation and
alteration of inorganic matter, from which it has originated.
It can be stated with a great dose of certainty that photosynthesis has
not emerged at once and spontaneously in one living cell or organism but it
has gone a long evolutionary way. This assumption is based on the diversity
of the living forms capable of photosynthesis and the differences in the
mechanisms which they resort to for its accomplishment. A lot of them have
been treated in detail in the “Biochemistry” by A. Lehninger (1976).
Not only eukaryotes (higher plants, unicellular and multicellular algae,
euglens, dinoflagellates, etc.) are endowed with the capacity for
photosynthesis, but also some prokaryotes (blue-green algae, green and
purple bacteria) can do it. The purple bacteria are obligatory anaerobes.
They inhabit the soil and bottom of water basins (swamps, lakes, seas and
oceans) that are rich in hydrogen sulphide, sulphates and native sulphur. It
is accepted that one of the donors of electrons for the reduction of CO₂ in