Organisms and Environmental Factors 15
2.5 PhotoSynthESiS —rESPiration—
chEMoSynthESiS
During photosynthesis, solar energy is converted into chemical energy
through the excitation of the electrons of chlorophyll by the photons of solar
radiation. The chemical energy is stored via the ADP → ATP reaction . At
the same time, the photons cause photolysis of the water, again via chlorophyll. The breakdown of H 2 O gives O 2 , which is freed into the environment, while the H 2 is used to synthesize organic compounds. The reactions
of the first stage of photosynthesis result in the manufacture of glucose,
according to the overall equation:
6
6
6
2
2
6 12 6
2
CO
H O light energy C H O
O
+
+
→
+
Then the glucose molecules bind to nitrogen and other substances, resulting in the complex organic compounds. The reactions are endothermic, and
the energy required is provided through the breakdown of ATP into ADP.
During chemosynthesis, the cells take the energy required through oxidation of organic or inorganic substances, via the process of respiration.
Oxidation is the removal of electrons, whereas reduction is the addition
of electrons. When an organic material is oxidized biochemically, it loses
electrons, generally in the form of hydrogen atoms. The H that is removed is
transported to the final recipient by a series of enzymes. In the case where the
final recipient of the H atoms is O 2 (of the air or water), H 2 O is formed and the
oxidation is called aerobic, whereas in all other cases it is called anaerobic .
The chemical energy produced is stored via the ADT → ATP reaction.
Aerobic respiration is shown in the overall equation:
Organic matter O
CO H O heat
+
→
+
+
2
2
2
All plants and animals and most of the other organisms draw energy
through the process of aerobic respiration. There are, however, certain categories of bacteria that carry out anaerobic respiration: as final recipients of
the H atoms, they use SO 4
= in producing H 2 S, NO 3
– in producing N 2 , CO 2
in producing CH 4 , etc. These bacteria are either strictly anaerobic, that is,
they appear only in conditions where O 2 is absent, or facultative, that is,
aerobic in the presence of O 2 and anaerobic in the absence of O 2 .
During reduction of CO 2 , methane CH 4 is produced. An odourless,
non-toxic gas, methane is a well-known product of septic (anaerobic) processes. When mixed with atmospheric air in various proportions, methane
gives an explosive gaseous mixture, which may cause serious accidents in
waste cleaning works and sewers. Particularly well known because of its
strong unpleasant odour, and also very toxic, is hydrogen sulphide H 2 S.
2.5 PhotoSynthESiS —rESPiration—
chEMoSynthESiS
During photosynthesis, solar energy is converted into chemical energy
through the excitation of the electrons of chlorophyll by the photons of solar
radiation. The chemical energy is stored via the ADP → ATP reaction . At
the same time, the photons cause photolysis of the water, again via chlorophyll. The breakdown of H 2 O gives O 2 , which is freed into the environment, while the H 2 is used to synthesize organic compounds. The reactions
of the first stage of photosynthesis result in the manufacture of glucose,
according to the overall equation:
6
6
6
2
2
6 12 6
2
CO
H O light energy C H O
O
+
+
→
+
Then the glucose molecules bind to nitrogen and other substances, resulting in the complex organic compounds. The reactions are endothermic, and
the energy required is provided through the breakdown of ATP into ADP.
During chemosynthesis, the cells take the energy required through oxidation of organic or inorganic substances, via the process of respiration.
Oxidation is the removal of electrons, whereas reduction is the addition
of electrons. When an organic material is oxidized biochemically, it loses
electrons, generally in the form of hydrogen atoms. The H that is removed is
transported to the final recipient by a series of enzymes. In the case where the
final recipient of the H atoms is O 2 (of the air or water), H 2 O is formed and the
oxidation is called aerobic, whereas in all other cases it is called anaerobic .
The chemical energy produced is stored via the ADT → ATP reaction.
Aerobic respiration is shown in the overall equation:
Organic matter O
CO H O heat
+
→
+
+
2
2
2
All plants and animals and most of the other organisms draw energy
through the process of aerobic respiration. There are, however, certain categories of bacteria that carry out anaerobic respiration: as final recipients of
the H atoms, they use SO 4
= in producing H 2 S, NO 3
– in producing N 2 , CO 2
in producing CH 4 , etc. These bacteria are either strictly anaerobic, that is,
they appear only in conditions where O 2 is absent, or facultative, that is,
aerobic in the presence of O 2 and anaerobic in the absence of O 2 .
During reduction of CO 2 , methane CH 4 is produced. An odourless,
non-toxic gas, methane is a well-known product of septic (anaerobic) processes. When mixed with atmospheric air in various proportions, methane
gives an explosive gaseous mixture, which may cause serious accidents in
waste cleaning works and sewers. Particularly well known because of its
strong unpleasant odour, and also very toxic, is hydrogen sulphide H 2 S.