Автор: Пользователь скрыл имя, 13 Декабря 2012 в 23:55, курсовая работа
Photosynthesis is arguably the most important biological process on earth. By liberating oxygen and consuming carbon dioxide, it has transformed the world into the hospitable environment we know today. Directly or indirectly, photosynthesis fills all of our food requirements and many of our needs for fiber and building materials. The energy stored in petroleum, natural gas and coal all came from the sun via photosynthesis, as does the energy in firewood, which is a major fuel in many parts of the world.
Introduction
General Information
Evolution
Overview of Cycle Between Autotrophs and Heterotrophs
Photosynthetic Membranes and Organelles
Light-Independent Reactions
On Land
In Water
Cyanobacteria
Purple Non-sulfuric Bacteria
Green Sulfur Bacteria
Conclusion
References
Appendix 1
Appendix 2
Purple bacteria
These give them colors ranging between purple, red, brown, and orange. Photosynthesis takes place at reaction centers on the cell membrane, which is folded into the cell to form sacs, tubes, or sheets, increasing the available surface area.
Like most other photosynthetic bacteria, purple bacteria do not produce oxygen, because the reducing agent (electron donor) involved in photosynthesis is not water. In some, called purple sulfur bacteria, it is either sulfide or elemental sulfur. The others, called purple non-sulfur bacteria, typically use hydrogen although some may use other compounds in small amounts. At one point these were considered families, but RNA trees show the purple bacteria make up a variety of separate groups, each closer relatives of non-photosynthetic proteobacteria than one another.
Purple bacteria were the first bacteria discovered to photosynthesize without having an oxygen byproduct. Instead, their byproduct is sulfur. This was proved by first establishing the bacteria's reactions to different concentrations of oxygen. What was found was that the bacteria moved quickly away from even the slightest trace of oxygen. Then a dish of the bacteria was taken, and a light was focused on one part of the dish leaving the rest dark.
As the bacteria cannot survive without light, all the bacteria moved into the circle of light, becoming very crowded. If the bacteria's byproduct was oxygen, the distances between individuals would become larger and larger as more oxygen was produced. But because of the bacteria's behavior in the focused light, it was concluded that the bacteria's photosynthetic byproduct could not be oxygen.
Researchers have theorized that some purple bacteria are related to the mitochondria, symbiotic bacteria in plant and animal cells today that act as organelles. Comparisons of their protein structure suggests that there is a common ancestor.
Purple sulfur bacteria are included among the gamma subgroup, and make up the order Chromatiales. The similarity between the photosynthetic machinery in these different lines indicates it had a common origin, either from some common ancestor or passed by lateral transfer.
Purple non-sulfur bacteria are found among the alpha and beta subgroups, including:
Rhodospirillales
Rhodospirillaceae e.g. Rhodospirillum
Acetobacteraceae e.g. Rhodopila
Rhizobiales
Bradyrhizobiaceae e.g. Rhodopseudomonas palustris
Hyphomicrobiaceae e.g. Rhodomicrobium
Rhodobiaceae e.g. Rhodobium
Other families
Rhodobacteraceae e.g. Rhodobacter
Rhodocyclaceae e.g. Rhodocyclus
Comamonadaceae e.g. Rhodoferax
Green sulfur bacteria
The green sulfur bacteria are a family of obligatory anaerobic photoautotrophic bacteria. Most closely related to the distant Bacteroidetes, they are accordingly assigned their own phylum.
Green Bacteria
Green sulfur bacteria are non-motile (except Chloroherpeton thalassium, which may glide) and come in spheres, rods, and spirals. Photosynthesis is achieved using bacteriochlorophyll (BChl) c, d, or e, in addition to BChl a and chlorophyll a, in chlorosomes attached to the membrane. They use sulfide ions, hydrogen or ferrous iron as an electron donor and the process is mediated by the type I reaction centre and Fenna-Matthews-Olson complex. Elemental sulfur deposited outside the cell may be further oxidized. By contrast, the photosynthesis in plants uses water as electron donor and produces oxygen.
Chlorobium tepidum has emerged as a model organism for the group, and although only ten genomes have been sequenced, these are quite comprehensive of the family's biodiversity. The apparent absence of two-component histidine-kinases and response regulators suggest limited phenotypic plasticity. Their small dependence on organic molecule transporters and transcription factors also indicate that these organisms are adapted to a narrow range of energy-limited conditions, an ecology shared with the simpler cyanobacteria, Prochlorococcus.
A species of green sulfur bacteria has been found living near a black smoker off the coast of Mexico at a depth of 2,500 meters beneath the surface of the Pacific Ocean. At this depth, the bacterium, designated GSB1, lives off the dim glow of the thermal vent since no sunlight can penetrate to that depth.
The population may include the species, Chlorobium ferrooxidans.
Scientific classification
Domain: Bacteria
Phylum: Chlorobi
Class: Chlorobia
Order: Chlorobiales
Family: Chlorobiaceae
Genera
Chlorobium
Chloroherpeton
Clathrochloris
Pelodictyon
Prosthecochloris
Conclusion
Making a conclusion we can row a parallel through 3 types of photosynthetic bacteria. Cyanobacteria carry out oxygenic photosynthesis, and purple and green bacteria use anoxygenic photosynthesis. Green sulfur bacteria are obligatory anaerobic photolithoautotrophs that use hydrogen sulfide, elemental sulfur, and hydrogen as electron sources. Cyanobacteria carry out oxygenic photosynthesis by means of photosynthetic apparatus similar to that of the eucaryotes. Like the red algae, they have phycobilisomes. Photosynthetic green and purple bacteria differ from eucaryotes and cyanobacteria in processing bacteriochloropyll and lacking photosystem II. Thus they cannot use the non cyclic pathway to form NADPH and O2. In photosynthesis, eucaryotes and cyanobacteria trap light energy with chlorophyll and accessory pigments and move electrons through photosystem I and II to make ATP and NADPH (the light reaction).
The above examples illustrate the importance of photosynthesis as a natural process and the impact that it has on all of our lives. Research into the nature of photosynthesis is crucial because only by understanding photosynthesis can we control it, and harness its principles for the betterment of mankind. Science has only recently developed the basic tools and techniques needed to investigate the intricate details of photosynthesis. It is now time to apply these tools and techniques to the problem, and to begin to reap the benefits of this research.
References
Appendix 1
Examples of photosynthetic organisms: leaves from higher plants flanked by colonies of photosynthetic purple bacteria (left) and cyanobacteria (right).
Appendix 2
Oxygenic Photosynthetic Bacteria.
Representative cyanobacteria. (a) Chroococcus turgidus, two colonies of four cells each (X600). (b) Nostoc with heterocysts (X550). (c) Oscillatoria trichomes seen with Nomarski interference-contrast optics (X250). (d) The cyanobacteria Anabaena spiroides and Microcystis aeruginosa. The spiral A. spiroides is covered with a thick gelatinous sheath (X 1,000).