|This article needs additional citations for verification.Please help improve this article by adding reliable references. Unsourced material may be challenged and removed. (August 2007)|
Living organisms use light energy to synthesize chemical energy. .It is arguably the most important biochemical pathway*1>, since nearly all life depends on it.This complex process occurs in plants such as cyanobacteria, phytoplankton, algae, and even in higher organisms such as phytoplankton.Photoautotrophs*1 are also referred to as photosynthetic organisms.
The word is derived from photo-, light, and synthesis, putting together.
Additional recommended knowledge
G3P is made from light energy and carbon dioxide in photosynthesis.In general, G3P is considered the chief end product of photosynthesis.
This is a common but somewhat simplified equation for photosynthesis:
When written as a word equation the light energy appears above the arrow as it is required for photosynthesis but it is not actually a reactant. Here the monosaccharide glucose is shown as a product, although the actual processes in plants produce disaccarides.
The equation is often presented in introductory chemistry texts in an even more simplified form as:<2>6 CO2(gas) + 6 H2O(liquid) + photons → C6H12O6(aqueous) + 6 O2(gas)
The photosynthesis process has two stages.A series of light-dependent reactions known as photosynthetic reactions (also called the Light reactions) captures the energy of light and uses it to produce molecules of high energy.A second stage is the light-independent reactions (also called the Calvin-Benson Cycle, but formerly referred to as the Dark Reactions) that make carbohydrates by trapping CO2.
When chlorophyll absorbs a photon, it loses an electron.Pheophytin, an oxygen-reduced form of chlorophyll, passes the electron to quinones, which announce the start of an electron flow that ultimately reduces NADP to NADPH.Additionally, it creates a proton gradient between the chloroplast and the outer membrane; ATP synthase utilizes this gradient to produce ATP.In a process called photolysis, the chlorophyll molecule re-gains the lost electron by taking it from a water molecule. This releases oxygen gas.
In the light-independent or dark reactions, RuBisCO combines carbon dioxide with water to create sugars. The newly formed NADPH, in an enzyme-mediated process known as the Calvin-Benson cycle, allows the sugars to be converted into sucrose and starch.
Living organisms must convert light energy into chemical energy in order to perform photosynthesis.
Basically, plants are photoautotrophs, and they can synthesize food directly from inorganic compounds with the aid of light energy - such as from the sun - instead of eating other organisms or acquiring nutrients from them.Chemical autotrophs, on the other hand, utilize energy from inorganic compounds rather than light energy.
Plants produce oxygen by reducing water, which ultimately comes from absorbed photons. As a byproduct, photosynthesis releases carbon dioxide as a waste product.Photoautotrophs use ATP and NADPH, which are derivations of light energy, for the synthesizing process.Under the condition of non-cyclic electron flow in green plants, the following equation describes the overall light-dependent reactions:
By using chemical energy, plants fix carbon dioxide into carbohydrates and other organic compounds without the need for light.An overall equation for carbon fixation (sometimes referred to as carbon reduction) in green plants is:
The carbon fixation process produces an intermediate product, which is then converted into the final carbohydrate products. .In plants and animals, the latter occurs when the energy from plants gets passed along in a food chain.heterotrophs are organisms that rely on photosynthetic and chemosynthetic processes for growth.Cellular respiration is in general the inverse of photosynthesis in that glucose and other compounds are oxidised to produce carbon dioxide, water, and chemical energy.Both processes, however, occur in different cellular compartments and are affected by different chemical reactions.
Light is absorbed primarily by chlorophyll, which is why most plants are green.As well as chlorophyll, other pigments such as carotenes and xanthophylls support its function.As well as chlorophyll, accessory pigments are found in chloroplasts, which are small organelles within the cell.While all cells of a plant have chloroplasts, most of the energy is captured by the leaves.A leaf's interior tissues, called the mesophyll, contain between 450,000 and 800,000 chloroplasts per square millimeter.Throughout the leaf, a water-resistant waxy cuticle is used to inhibit excessive evaporation of water and reduce the absorption of ultraviolet light to reduce heating.During photosynthesis, light passes through the epidermis layer to reach the palisade mesophyll cells.
Plants can absorb 90% of the light that hits them, whereas commercial solar panels are only able to absorb 30% of the light.Chlorophyll molecules spend a long time in a superposition of states.
In algae and bacteria
Various types of algae exist, including organisms like kelp, as well as microscopic, single-cell organisms.Plants that live on water undergo the same biochemical process as land plants. .Algae produce oxygen in all forms, and many of them are autotrophic.However, some organisms are heterotrophic, relying on materials produced by other organisms.Zooxanthellae and coral polyps have a mutualistic relationship in coral reefs, for example.
Chloroplasts (or any membrane-bound organelles) are not found in photosynthetic bacteria.This is the reason why they perform direct photosynthesis within their cells.The cyanobacteria have membranes similar to those in chloroplasts and are the only prokaryotes that perform oxygen-producing photosynthesis.It is now widely believed that chloroplasts evolved from a symbiotic bacterium, which was also an ancestor of cyanobacteria.They also produce oxygen, but they have pigments called bacteriochlorophylls.For photosynthesis, bacteria like Chromatium oxidize hydrogen sulfide instead of water, generating sulfur waste as a result.
Living organisms benefit from the ability to convert light energy into chemical energy.Photosynthetic systems, such as those in green and purple sulfur bacteria as well as in green and purple non-sulfur bacteria, were predicted to be anoxygenic, using various molecules as electron donors.Hydrogen and sulfur are thought to be electron donors in green and purple sulfur bacteria.Other organic acids were used by green non-sulfur bacteria.Purple nonsulfur bacteria utilized a variety of non-specific organic molecules.It is consistent with the geological evidence that the atmosphere was highly reduced during that time.
It is the evolution of oxygenic photosynthesis, sometimes called the oxygen catastrophe, that produces oxygen in the atmosphere.Geological evidence indicates oxygenic photosynthesis became increasingly important during the Paleoproterozoic period, approximately 2 billion years ago.Modern photosynthesis in plants and many other photosynthetic organisms is oxygenic.By absorbing a photon, the reaction center of oxygenic photosynthesis oxidizes water into molecular oxygen.
Origin of chloroplasts
In plants, chloroplasts are the cells that perform photosynthesis.The chloroplasts and photosynthetic bacteria have many similarities, including a circular chromosome, prokaryotic-type ribosomes, and similar proteins in the photosynthetic reaction center.
Endosymbiotic theory suggests that photosynthetic bacteria were acquired by eukaryotic cells (by endocytosis or gene fusion) to form the first plant cells.Thus, chloroplasts may simply be primitive photosynthetic bacteria that have adapted to life inside plant cells, whereas plants themselves do not seem to have evolved photosynthetic abilities.Likewise, mitochondria are also found in complex animals, such as humans, whose cells use them as a source of energy; mitochondria are believed to have evolved from endosymbiotic bacteria, which are related to the present-day Rickettsia bacteria.Both chloroplasts and mitochondria have their own DNA, separate from the nuclear DNA of their animals or plants.
A symbiotic relationship of marine mollusks Elysia viridis and Elysia chlorotica with algae with similar chloroplast structures shows support for this contention.They do not transfer these chloroplasts to the next generation, however.
Cyanobacteria and the evolution of photosynthesis
Cyanobacteria use water as a source of electrons during photosynthesis because the skill evolved once in a common ancestor.Wordtune couldn't crunch your text. Try it on a shorter text.