Courses : Cell Biology
Credit Hours : 3 Credit
Semester/Credit : 2 Sememster, 2022/2023
nd
EVOLUTION OF PLANT PHOTOSYNTHESIS C3, C4, CAM
The geological evidence for the evolution of photosynthesis is scanty, because Photosynthesis is
a biochemical process involving proteins and other organic molecules that rapidly decompose.
Hypothesis about the evolutionary development of photosynthesis was put forward by Schopf
(1978) in Lawlor (1993) and Bendall (1986) in Lawlor (1993). Earth formed approximately 4.6 x
109 years ago (Figure 1) and for the first 0.5 x 109 years the earth became cold and solid. Earth's
distance from the sun and the size of the earth determine heat received and the force that holds
the gas on the surface, so water and the atmosphere still on earth. The primitive atmosphere was
highly reduced and contained methane (CH4), H2, H2S, CO2, NH3 and others, but does not
contain O2 or contains under anoxic conditions (Lawlor, 1993).
This condition without O2 is essential for the evolution of life because of O2 destroy organic
molecules. The primitive earth's atmosphere also did not contain it ozone which is a thin layer in
the upper atmosphere and functions to absorbs ultra violet (UV) light. Radiation, high
temperature and various kinds gas involved in volcanic activity, allowing synthesis to occur
organic molecules. How biological systems reproduce themselves little is known about this
condition. But the facts show it is organisms with a size and cell structure similar to bacteria in
rock which is 3.5 x 109 years old. A type of metabolism that involves light probably took place at
that time because carotenoid derivatives were detected in rocks of that era. It is possible that
these primitive organisms synthesized ATP with protons moved by light as it does in bacteria
Halobacterium halobium. Organic carbon from deposits at this time shows discrimination against
the 13C isotope and this proves that photosynthesis occurred early in evolution. The organism is
able to provide ATP itself by exploiting an abundant source of energy
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Several processes are associated with the light reaction (phase I of photosynthesis) and flow
electrons as well as ATP including the assimilation of N2, CO2 and S. But not water molecules
broken down in primitive photosynthesis until 3.5 x 109 years ago, so no O2 is produced in
photosynthesis and the atmosphere is reduced. After the evolution of the process of breaking
water molecules that require energy light passes through 2 photosystems, water can be oxidized
and O2 is released into the atmosphere. Much evidence supports the evolutionary time scale for
this process (Schopf 1978 in Lawlor 1993). Thick layers of fossilized limestone, called
stromatolites, were formed 3 x 109 years ago and contains blue green algae which are also found
on modern stromatolites. But O2 production may have happened before. Some geochemical
processes may also consume O2, for example ferrous ions (Fe2+) produces insoluble Fe3O2.
Fe2+ content in the oceans maybe depleted due to deposition of iron ore. This process results in
the formation of layers red in time 2.2 x 109 – 1.7 x 109 years ago. Generated oxygen by the
breakdown of H2O molecules by too little UV light to allow a sharp decrease in Fe2+. Uraninite
(UO2) is a uranium ore which is insoluble under conditions with O2 concentrations above 1%
and UO2 deposits younger than 2 x 109 years ago was not found. So, between 3.5 x 109 and 3.0
x 109 years ago photosynthesis developed with using H2O as a reductant and increasing O2 in
the atmosphere (Lawlor, 1993). Reduced carbon deposition may have contributed to the decline
carbon content and an increase in O2 in the atmosphere. At that time concentration CO2 is
probably several hundred times greater than it is today. Up to 1.5 x 109 – 1.0 x 109 years ago, the
earth's conditions began to be aerobic because of the buffer chemical consumables and O2
pressure of more than 1 kPa. Oxygen in the atmosphere part above forms the ozone layer which
absorbs ultra violet radiation, resulting in the evolution of higher organisms and life on land
begins. O2 increases the amount of energy for respiration as much as 10 times by acting as
terminal receptor for the process of photosynthesis. Most of the living organisms today, including
humans, depend on the O2 produced in the process Photosynthesis
Eukaryotes, consisting of cells with nuclei, may develop in depth early life on earth, based on
evidence for the existence of sterants (molecules a sterol derivative thought to be made only by
nucleated cells such as eukaryotes) in rocks at 1.7 x 109 years ago. These eukaryotes thrive since
1 x 109 years ago and formed macroscopic organisms and multinucleate (both plant and animal).
this development process possibly related to climate change around 900-600 million years ago
due to tectonic and volcanic activity, the loss of large amounts of carbon with buried as sediment
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as well as the start of global climate change including formation of ice rivers. Evidence of the
structure and function of nucleic acids in chloroplasts and the mitochondria of higher plants
show that these organelles are bacteria and blue-green algae that enter eukaryotic cells not
photosyn Photosynthesis develops to become more biochemically complex and occurs
separation between respiration and photosynthesis and their regulation. Photosynthesis shape the
biosphere both directly and through its effects on the climate and earth geology. The carbon
element from photosynthesis makes up oil, coal and gas, so that the CO2 in the atmosphere
decreases and the O2/CO2 ratio increases. this condition may be unfavorable for photosynthesis
because of the linilose bisphosphate enzyme carboxylase which fixes CO2 works less efficiently.
On land the loss of water of the plant which is prevented by the presence of a thick cuticle, also
reduces CO2 supply. Evolution of photosynthetic types such as C4 and CAM is possible is a
response to a decrease in the CO2/O2 ratio and more atmosphere dry with intense radiation.
Human activity is currently increasing concentration of CO2 in the atmosphere by burning fossil
fuels (Lawlor, 1993). This may improve plant growth in a short time and will also affect the
world's climatethesizing
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