Photosynthesis

PHOTOSYNTHESIS Photosynthesis is a process used by plants and other organisms to convert light energy into chemical energy that can later be released to fuel the organisms' activities (energy transformation). This chemical energy is stored in carbohydrate molecules, such as sugars, which are synthesized from carbon dioxide and water – hence the name photosynthesis, from the Greek φῶς, phōs, "light", and σύνθεσις, synthesis, "putting together". In most cases, oxygen is also released as a waste product. Most plants, most algae, and cyanobacteria perform photosynthesis; such organisms are called photoautotrophs. Photosynthesis is largely responsible for producing and maintaining the oxygen content of the Earth's atmosphere, and supplies all of the organic compounds and most of the energy necessary for life on Earth. Although photosynthesis is performed differently by different species, the process always begins when energy from light is absorbed by proteins called reaction centres that contain green chlorophyll pigments. In plants, these proteins are held inside organelles called chloroplasts, which are most abundant in leaf cells, while in bacteria they are embedded in the plasma membrane. In these light-dependent reactions, some energy is used to strip electrons from suitable substances, such as water, producing oxygen gas. The hydrogen freed by the splitting of water is used in the creation of two further compounds that serve as short-term stores of energy, enabling its transfer to drive other reactions: these compounds are reduced nicotinamide adenine dinucleotide phosphate (NADPH) and adenosine triphosphate (ATP), the "energy currency" of cells. In plants, algae and cyanobacteria, long-term energy storage in the form of sugars is produced by a subsequent sequence of light-independent reactions called the Calvin cycle; some bacteria use different mechanisms, such as the reverse Krebs cycle, to achieve the same end. In the Calvin cycle, atmospheric carbon dioxide is incorporated into already existing organic carbon compounds, such as ribulose bisphosphate (RuBP). Using the ATP and NADPH produced by the light-dependent reactions, the resulting compounds are then reduced and removed to form further carbohydrates, such as glucose.

2015

All living organisms on earth consist of one or more cells. Each cell runs on the chemical energy found mainly in carbohydrate molecules (food), and the majority of these molecules are produced by one process: photosynthesis. Through photosynthesis, certain organisms convert solar energy (sunlight) into chemical energy, which is then used to build carbohydrate molecules. The energy used to hold these molecules together is released when an organism breaks down food. Cells then use this energy to perform work, such as cellular respiration.

Books in Soils, Plants, and the Environment, 2005

Solar light can be efficiently captured and converted into chemical energy by all phototrophs, including photosynthetic bacteria, cyanobacteria, algae, and vascular plants, through their specific photosynthetic machinery. The major environmental challenge to photosynthetic organisms is the variability in the light. To cope with the rapidly fluctuating light environment (specifically in intensity and wavelength distribution), the phototrophs have evolved complex regulatory systems to adapt to changing light conditions. Advanced understanding of the adaptive mechanisms developed by photosynthetic organisms will inform the bioengineering of phototrophs to enhance the utilization of solar energy, for the production of biofuel and commodity products from light, CO 2 , and water. In this chapter, we will summarize recent studies on the molecular basis underlying the physiological adaptation and regulation of photosynthetic machinery, in particular, in cyanobacteria, toward irradiance variation. 3.1 PHOTOSYNTHETIC APPARATUS: COMPOSITION AND ORGANIZATION The primary reactions of photosynthesis are mediated by a series of photosynthetic complexes associated with or embedded in the photosynthetic membranes. These pigment-protein complexes can be classified into several groups according to their functions: light-harvesting antenna complexes, photosynthetic reaction centers (RCs), the cytochrome (Cyt) complex, and ATP synthase (ATPase). They are structurally and functionally linked in order through the photosynthetic electron transport chain (Figure 3.1). Light energy captured by the light-harvesting antenna is rapidly and efficiently transferred to the RCs to drive the transmembrane charge separation. The electrons are then transferred to the (plasto)quinone pool and subsequently to the Cyt enzymes. The electron transfer reactions are coupled to the formation of an electrochemical gradient across the photosynthetic membranes, which is essential for driving the ATP synthesis.

PLANT PHYSIOLOGY, 1959

RABINOWITCH-PRIMARY PROCESSES IN PHOTOSYNTHESIS tide reactions in Chromatium. Biochim. Biophys. Acta. (In press.) 11. OLSON, J. M. and AMESZ, J. Action spectra for fluorescence excitation of pyridine nucleotide in photosynthesizing bacteria and algae. Biochim. Biophys. Acta. (In press.) 12. SAN PIETRO, A. and LANG, H. M. Accumulation of reduced pyridine nucleotide by illuminated grana. Science 124: 118. 1956.

Chapter 9: photosynthesis  Photosynthesis: process where living organism use light energy to generate chemical energy that drives anabolic reactions which converts Co2 and H2O into glucose and other carbohydrates  Organism are autotrophs: use inorganic substance to form organic molecules  Heterotrophs: they meet their nutritional requirement by consuming either autotrophs and other heterotrophic organism that feed upon autotrophs  Eukaryotic photosynthesis Chloroplast  Occur In plant mesophyll tissue  Made up of an inner and outer membrane layer o Bounded by the inner membrane : stroma  Contains carbohydrate-producing enzymes  Flats structures: thylakoids  Made of membranes : contains photosynthetic pigments  Fluids interior of is the thylakoid space  Grana are stacked of thylakoids  Grana can be joined to another through a membrane that extends between two thylakoids o Photosynthesizing prokaryotes lack stromas, they do contains thylakoid membranes : occurs as infolding of the plasma membrane  Phycocyanin: blue pigment  Chemical reaction o 6CO 2 + 12 H 2 O  (light energy + chlorophyll)  C 6 H 12 O 2 + 6 O 2 o Water is reduce to CO2  carbohydrate formation o Very low energy state of the hydrogen attaches to the oxygen in a H2O molecules o H2O transferring electron: unfavorable o Light energy is absorb by the chlorophyll: provides the driving force to reduce O2 during photosynthesis and thus enables the reaction to proceed  Can be o Light dependent reaction o Carbon fixation reaction Light-dependent reactions of photosynthesis: general Overview -thylakoids

Bioelectrochemistry and Bioenergetics, 1990

consists essentially in the conversion, by the plant kingdom, of sunlight energy into chemical energy (cell material and molecular oxygen). From a physicochemical point of view, photosynthesis is intrinsically a light-driven oxidation-reduction/acid-base process. In the course of photosynthesis, water is oxidized to molecular oxygen, whereas carbon dioxide, nitrate or dinitrogen, and sulfate are respectively reduced to carbohydrate, ammonia and sulfide; water is moreover ionized, in similar amounts, into protons and hydroxide anions. Phosphorus does not change its oxidation state, but orthophosphate becomes energized to metaphosphate, at the expense of the ionization products of water, in a peculiar acid-base process. Metaphosphate is mostly used as an energy shuttle in many cell processes, among them in the reduction and assimilation of the primordial bioelements, as well as in the polymerization of the resulting monomers -sugars, lipid components, amino acids, nucleotides -and deenergizes itself back to orthophosphate, again in acid-base reactions. The role of the oxide anion, that is, an oxygen atom with two additional electrons, 02-, m these bioenergetic processes is especially discussed.

While many bacteria carry out a simple form of photosynthesis using a single photosystem, cyanobacteria, algae, and plants perform oxygenic photosynthesis using two photochemical systems, connected in series. In the latter, water is oxidized to molecular oxygen, and organic compounds are produced from inorganic carbon compounds. It is a very complex process, which has several phases starting with absorption of light by pigments in antenna complexes, and channeling of the excitation energy to the reaction centers, where positive and negative charges are separated. The positive charges, obtained from PSII, are used to oxidize water in a four-step process involving manganese in several oxidation states, whereas the negative charges are transferred over a number of electron carriers, most of which are bound to membrane proteins, but there are also carriers in the membrane lipids or in water. PSI is involved in taking the electrons coming from PSII to the next level; the negative charges are finally used to reduce NADP+ . The electron transfer is coupled to transfer of protons across the membranes, which together with protons from the oxidation of water leads to energy stored in the form of a pH difference across the membranes. The energy, thus transiently stored, is used for the synthesis of ATP. The ATP is used, together with NADPH, for the synthesis of carbohydrate from carbon dioxide or bicarbonate.Oxygenic photosynthesis is the main process that provides energy to the entire biosphere of our planet. It also gives rise to the ozone layer that protects us from solar ultraviolet radiation. Furthermore, by its consumption of carbon dioxide, it has for a long time kept the climate friendly to life, and it has been an indirect cause of various geological processes. There is now hope that by learning more about natural photosynthesis we shall be able to better address humanity’s energy problems by harvesting solar energy in an economically feasible, environment-friendly, and sustainable way.

Religions, 2021

The Tibetan yoga practice known as “winds, channels, and inner heat” (rtsa rlung gtum mo) is physically challenging and yet is intentionally designed to transform the mind. This chapter explores the relationship between Buddhist doctrine and this physical practice aimed at enlightenment through the teachings of a contemporary yoga master at Namdroling Tibetan Buddhist Monastery and Nunnery in Bylakuppe, Karnataka, South India. This ethnographic profile exemplifies the role of a modern Tibetan lama who teaches a postural yoga practice and interprets the text and techniques for practitioners. While many modern postural yoga systems are divorced from religious doctrine, Tibetan Buddhist yoga is not. This essay highlights three key areas of Buddhist doctrine support the practice of Sky Dharma (gNam chos) yoga at Namdroling: (1) The history and legacy that accompany the practice, which identify the deity of Tibetan yoga as a wrathful form of Avalokite´svara, the Buddha of compassion; (2) The role of deity yoga in the practice of Tibetan yoga, where the practitioner arises as the deity during yoga practice, an all-consuming inner contemplation; and (3) The framing of Tibetan yoga within the wider philosophy of karma theory and its relationship to Buddhist cosmology. Practitioners of Tibetan yoga endeavor to burn up karmic seeds that fuel the cycle of rebirth in the six realms of "samsara." In Tibetan yoga, the body acts in service of the text, the philosophy, and the mind to increasingly link the logic of texts to experience in meaningful ways.