Photosynthesis is the primary energy conversion method that fuels the plant world and, by extension, the animal world. In converting light energy to chemical energy, photosynthesis is the core building block of almost all life on this planet. Understanding the basic elements of photosynthesis allows a greater understanding of the impact of energy sources on life. Show
The Need to FeedLife is supported by spending energy. Without energy, life is impossible. However, energy, to be as useful as possible, must be present in a form that can be stored, moved and used as needed rather than being used only when present from an outside source. There are a number of forms of energy that can be used to support life--some bacteria appear to gain their energy in the form of heat from deep sources venting from under the Earth's crust, for example. However the most commonly available form of energy on the planet is from the sun, in the form of light. Photosynthesis is the process of collecting that energy and converting it into a chemical substance that can be manipulated to the advantage of the plant. ChlorophyllChlorophyll is the conversion engine turning light energy into sugars. Chlorophyll is contained in membranes called chloroplasts, found in the interior of cells. The majority of the chlorophyll found in these chloroplasts collects and transfers light energy to two chlorophyll reaction centers in the network of chloroplasts. These pairs perform the actual work of conversion from light energy to sugars, using hydrogen and carbon, producing glucose, and putting off oxygen as a by-product of photosynthesis. ProcessWhen light hits the chlorophyll in a leaf, its is passed to the paired chlorophylls in the reactive center, which use the energy directly to combine water, carbon and oxygen into a new physical arrangement: glucose, a simple plant sugar. The rearrangement, when disassembled, releases energy that can be used in other physical processes. There is energy lost in the process; no conversion of energy from one form to another is 100 percent efficient. The advantage of the process, however, is a form of energy that can be used as it is or further stored and manipulated. Further StagesAfter photosynthesis has occurred, the glucose in the plant may be converted into two more easily stored forms of chemical energy: complex carbohydrates and lipids, better known as starches and fats. Starch and fat are warehouse stores for a plant, which can be held or transported in phloem tissue for future uses. Centrality of Plant EnergyPlants, and plants alone, produce food from light. No animal is capable of doing so. Thus, all plants are considered "producers" and animals "consumers" in the economy of energy use in bio-networks. Animals make use of plants as food, or eat other animals that once ate plants as food, but don't transform light into food themselves. Furthermore even non-food-based forms of energy are most often based on plant use. Wood, coal and oil are forms of plant that created and stored energy. While humans have begun to learn to use other forms of energy, from water-generated energy to nuclear energy to direct conversion of solar energy, the majority of our economic strength is still based on the plant's ability to combine light energy with carbon, oxygen and water to produce glucose. Top Questions Why is photosynthesis important?What is the basic formula for photosynthesis?Which organisms can photosynthesize?Summary Read a brief summary of this topicphotosynthesis, the process by which green plants and certain other organisms transform light energy into chemical energy. During photosynthesis in green plants, light energy is captured and used to convert water, carbon dioxide, and minerals into oxygen and energy-rich organic compounds. It would be impossible to overestimate the importance of photosynthesis in the maintenance of life on Earth. If photosynthesis ceased, there would soon be little food or other organic matter on Earth. Most organisms would disappear, and in time Earth’s atmosphere would become nearly devoid of gaseous oxygen. The only organisms able to exist under such conditions would be the chemosynthetic bacteria, which can utilize the chemical energy of certain inorganic compounds and thus are not dependent on the conversion of light energy. Energy produced by photosynthesis carried out by plants millions of years ago is responsible for the fossil fuels (i.e., coal, oil, and gas) that power industrial society. In past ages, green plants and small organisms that fed on plants increased faster than they were consumed, and their remains were deposited in Earth’s crust by sedimentation and other geological processes. There, protected from oxidation, these organic remains were slowly converted to fossil fuels. These fuels not only provide much of the energy used in factories, homes, and transportation but also serve as the raw material for plastics and other synthetic products. Unfortunately, modern civilization is using up in a few centuries the excess of photosynthetic production accumulated over millions of years. Consequently, the carbon dioxide that has been removed from the air to make carbohydrates in photosynthesis over millions of years is being returned at an incredibly rapid rate. The carbon dioxide concentration in Earth’s atmosphere is rising the fastest it ever has in Earth’s history, and this phenomenon is expected to have major implications on Earth’s climate. Requirements for food, materials, and energy in a world where human population is rapidly growing have created a need to increase both the amount of photosynthesis and the efficiency of converting photosynthetic output into products useful to people. One response to those needs—the so-called Green Revolution, begun in the mid-20th century—achieved enormous improvements in agricultural yield through the use of chemical fertilizers, pest and plant-disease control, plant breeding, and mechanized tilling, harvesting, and crop processing. This effort limited severe famines to a few areas of the world despite rapid population growth, but it did not eliminate widespread malnutrition. Moreover, beginning in the early 1990s, the rate at which yields of major crops increased began to decline. This was especially true for rice in Asia. Rising costs associated with sustaining high rates of agricultural production, which required ever-increasing inputs of fertilizers and pesticides and constant development of new plant varieties, also became problematic for farmers in many countries.  Britannica Quiz Biology Bonanza What does the word "migration" mean? How many sets of legs does a shrimp have? From poisonous fish to biodiversity, learn more about the study of living things in this quiz. A second agricultural revolution, based on plant genetic engineering, was forecast to lead to increases in plant productivity and thereby partially alleviate malnutrition. Since the 1970s, molecular biologists have possessed the means to alter a plant’s genetic material (deoxyribonucleic acid, or DNA) with the aim of achieving improvements in disease and drought resistance, product yield and quality, frost hardiness, and other desirable properties. However, such traits are inherently complex, and the process of making changes to crop plants through genetic engineering has turned out to be more complicated than anticipated. In the future such genetic engineering may result in improvements in the process of photosynthesis, but by the first decades of the 21st century, it had yet to demonstrate that it could dramatically increase crop yields. Another intriguing area in the study of photosynthesis has been the discovery that certain animals are able to convert light energy into chemical energy. The emerald green sea slug (Elysia chlorotica), for example, acquires genes and chloroplasts from Vaucheria litorea, an alga it consumes, giving it a limited ability to produce chlorophyll. When enough chloroplasts are assimilated, the slug may forgo the ingestion of food. The pea aphid (Acyrthosiphon pisum) can harness light to manufacture the energy-rich compound adenosine triphosphate (ATP); this ability has been linked to the aphid’s manufacture of carotenoid pigments. Get a Britannica Premium subscription and gain access to exclusive content. Subscribe Now General characteristicsDevelopment of the ideaThe study of photosynthesis began in 1771 with observations made by the English clergyman and scientist Joseph Priestley. Priestley had burned a candle in a closed container until the air within the container could no longer support combustion. He then placed a sprig of mint plant in the container and discovered that after several days the mint had produced some substance (later recognized as oxygen) that enabled the confined air to again support combustion. In 1779 the Dutch physician Jan Ingenhousz expanded upon Priestley’s work, showing that the plant had to be exposed to light if the combustible substance (i.e., oxygen) was to be restored. He also demonstrated that this process required the presence of the green tissues of the plant. In 1782 it was demonstrated that the combustion-supporting gas (oxygen) was formed at the expense of another gas, or “fixed air,” which had been identified the year before as carbon dioxide. Gas-exchange experiments in 1804 showed that the gain in weight of a plant grown in a carefully weighed pot resulted from the uptake of carbon, which came entirely from absorbed carbon dioxide, and water taken up by plant roots; the balance is oxygen, released back to the atmosphere. Almost half a century passed before the concept of chemical energy had developed sufficiently to permit the discovery (in 1845) that light energy from the sun is stored as chemical energy in products formed during photosynthesis. Overall reaction of photosynthesisIn chemical terms, photosynthesis is a light-energized
oxidation–reduction process. (Oxidation refers to the removal of electrons from a molecule; reduction refers to the gain of electrons by a molecule.) In plant photosynthesis, the energy of light is used to drive the
oxidation of water (H2O), producing oxygen gas (O2), hydrogen ions (H+), and electrons. Most of the removed electrons and hydrogen ions ultimately are transferred to carbon dioxide (CO2), which is reduced to organic products. Other electrons and
hydrogen ions are used to reduce nitrate and sulfate to amino and sulfhydryl groups in amino acids, which are the building blocks of
proteins. In most green cells, carbohydrates—especially starch and the sugar
sucrose—are the major direct organic products of photosynthesis. The overall reaction in which carbohydrates—represented by the general formula (CH2O)—are formed during plant photosynthesis can be indicated by the following equation: This equation is merely a summary statement, for the process of photosynthesis actually involves numerous reactions catalyzed by enzymes (organic catalysts). These reactions occur in two stages: the “light” stage, consisting of photochemical (i.e., light-capturing) reactions; and the “dark” stage, comprising chemical reactions controlled by enzymes. During the first stage, the energy of light is absorbed and used to drive a series of electron transfers, resulting in the synthesis of ATP and the electron-donor-reduced nicotine adenine dinucleotide phosphate (NADPH). During the dark stage, the ATP and NADPH formed in the light-capturing reactions are used to reduce carbon dioxide to organic carbon compounds. This assimilation of inorganic carbon into organic compounds is called carbon fixation. During the 20th century, comparisons between photosynthetic processes in green plants and in certain photosynthetic
sulfur bacteria provided important information about the photosynthetic mechanism. Sulfur bacteria use hydrogen sulfide (H2S) as a source of hydrogen atoms and produce
sulfur instead of oxygen during photosynthesis. The overall reaction is In the 1930s Dutch biologist
Cornelis van Niel recognized that the utilization of carbon dioxide to form organic compounds was similar in the two types of photosynthetic organisms. Suggesting that differences existed in the light-dependent stage and in the nature of the compounds used as a source of hydrogen atoms, he proposed that hydrogen was transferred from hydrogen sulfide (in bacteria) or water (in green
plants) to an unknown acceptor (called A), which was reduced to H2A. During the dark reactions, which are similar in both bacteria and green plants, the reduced acceptor (H2A) reacted with carbon dioxide (CO2) to form carbohydrate (CH2O) and to oxidize the unknown acceptor to A. This
putative reaction can be represented as: Van Niel’s proposal was important because the popular (but incorrect) theory had been that oxygen was removed from carbon dioxide (rather than hydrogen from water, releasing oxygen) and that carbon then combined with water to form carbohydrate (rather than the hydrogen from water combining with CO2 to form CH2O). By 1940 chemists were using heavy isotopes to follow the reactions of photosynthesis. Water marked with an isotope of oxygen (18O) was used in early experiments. Plants that photosynthesized in the presence of water containing H218O produced oxygen gas containing 18O; those that photosynthesized in the presence of normal water produced normal oxygen gas. These results provided definitive support for van Niel’s theory that the oxygen gas produced during photosynthesis is derived from water. What are the three characteristics of photosynthesis?To perform photosynthesis, plants need three things: carbon dioxide, water, and sunlight. for photosynthesis. Carbon dioxide enters through tiny holes in a plant's leaves, flowers, branches, stems, and roots. Plants also require water to make their food.
What are 5 facts about photosynthesis?10 Facts on Photosynthesis. The green color of leaves is due to chlorophyll. ... . The two main parts of a chloroplast are the grana and stroma. ... . The first stage of photosynthesis captures energy from the sun to break down water molecules. ... . The second stage of photosynthesis is the Calvin cycle.. What is the main characteristic of the first stage of photosynthesis?What is the First Stage of Photosynthesis? Stage one of photosynthesis is the light-dependent reaction, wherein the organism uses sunlight to make carrier molecules for energy. During this stage, sunlight interacts with chlorophyll, exciting its electrons to a higher energy state.
Is photosynthesis a characteristic of plants?Right from the tiny mosses to the large trees, there some unique characteristics of a plant that set them apart. All plants are eukaryotic, photosynthetic, and multicellular. Plants are multicellular organisms and they make food through the process of photosynthesis.
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What are the characteristics of photosynthesis
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