summarize.
Photosynthesis is a process used by plants and other organisms to convert light energy into chemical energy that, through cellular respiration, can later be released to fuel the organism's activities. Some of this chemical energy is stored in carbohydrate molecules, such as sugars and starches, which are synthesized from carbon dioxide and water – hence the name photosynthesis, from the Greek phōs (φῶς), "light", and synthesis (σύνθεσις), "putting together".[1][2][3] Most plants, 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 most of the energy necessary for life on Earth.[4]
Although photosynthesis is performed differently by different species, the process always begins when energy from light is absorbed by proteins called reaction centers that contain green chlorophyll (and other colored) pigments/chromophores. 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, sugars are synthesized by a subsequent sequence of light-independent reactions called the Calvin cycle. In the Calvin cycle, atmospheric carbon dioxide is incorporated into already existing organic carbon compounds, such as ribulose bisphosphate (RuBP).[5] 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. In other bacteria, different mechanisms such as the reverse Krebs cycle are used to achieve the same end.
The first photosynthetic organisms probably evolved early in the evolutionary history of life and most likely used reducing agents such as hydrogen or hydrogen sulfide, rather than water, as sources of electrons.[6] Cyanobacteria appeared later; the excess oxygen they produced contributed directly to the oxygenation of the Earth,[7] which rendered the evolution of complex life possible. Today, the average rate of energy capture by photosynthesis globally is approximately 130 terawatts,[8][9][10] which is about eight times the current power consumption of human civilization.[11] Photosynthetic organisms also convert around 100–115 billion tons (91–104 Pg petagrams, or billion metric tons), of carbon into biomass per year.[12][13] That plants receive some energy from light – in addition to air, soil, and water – was first discovered in 1779 by Jan Ingenhousz.
Photosynthesis is vital for climate processes, as it captures carbon dioxide from the air and then binds carbon in plants and further in soils and harvested products. Cereals alone are estimated to bind 3,825 Tg (teragrams) or 3.825 Pg (petagrams) of carbon dioxide every year, i.e. 3.825 billion metric tons.[14]
Photosynthesis is the process used by plants and other organisms to convert light energy into chemical energy that, through cellular respiration, can later be released to fuel the organism's activities. It is responsible for producing and maintaining the oxygen content of the Earth's atmosphere, and supplies most of the energy necessary for life on Earth. Photosynthesis involves the use of light energy to strip electrons from suitable substances, such as water, producing oxygen gas, and the use of the hydrogen freed to create two further compounds that serve as short-term stores of energy. In plants, algae and cyanobacteria, sugars are synthesized by a subsequent sequence of light-independent reactions called the Calvin cycle.
Photosynthesis is a process used by plants, algae, and cyanobacteria to convert light energy into chemical energy. This energy is then used to fuel the organism's activities through cellular respiration. During photosynthesis, plants and other photosynthetic organisms absorb light energy using proteins called reaction centers, which contain chlorophyll pigments. In plants, these proteins are located inside organelles called chloroplasts, while in bacteria they are embedded in the plasma membrane.
In the light-dependent reactions of photosynthesis, energy is used to strip electrons from substances like water, releasing oxygen gas in the process. The hydrogen released from the splitting of water is used to create two compounds called reduced nicotinamide adenine dinucleotide phosphate (NADPH) and adenosine triphosphate (ATP), which serve as short-term energy stores. These compounds transfer energy to drive other reactions within the organism.
In plants, algae, and cyanobacteria, the sugars necessary for growth and energy storage are synthesized in a sequence of light-independent reactions called the Calvin cycle. Carbon dioxide from the atmosphere is incorporated into existing organic carbon compounds, such as ribulose bisphosphate (RuBP), using the ATP and NADPH produced in the light-dependent reactions. These compounds are then reduced and transformed into carbohydrates, such as glucose, which can be used as an energy source.
Photosynthesis is responsible for producing and maintaining the oxygen content of the Earth's atmosphere, and it supplies most of the energy necessary for life on Earth. The process has evolved over billions of years, with early photosynthetic organisms likely using reducing agents like hydrogen or hydrogen sulfide as sources of electrons, rather than water. The appearance of cyanobacteria contributed to the oxygenation of the Earth's atmosphere, making complex life forms possible. Currently, photosynthesis globally captures approximately 130 terawatts of energy, which is about eight times the current power consumption of human civilization. Photosynthetic organisms also convert around 100-115 billion tons of carbon into biomass each year.
Photosynthesis plays a vital role in climate processes by capturing carbon dioxide from the air and storing carbon in plants, soils, and harvested products. Cereals alone are estimated to bind billions of metric tons of carbon dioxide every year. The discovery that plants receive energy from light was made in 1779 by Jan Ingenhousz.