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Photosynthesis - Science Clarified

Photosynthesis consists of two series of biochemical reactions, called the light reactions and the dark reactions. The light reactions use the light energy absorbed by chlorophyll to synthesize structurally unstable high-energy molecules. The dark reactions use these high-energy molecules to manufacture carbohydrates. The carbohydrates are stable structures that can be stored by plants and by bacteria. Although the dark reactions do not require light, they often occur in the light because they are dependent upon the light reactions. In higher plants and algae, the light and dark reactions of photosynthesis occur in chloroplasts, specialized chlorophyll-containing intracellular structures that are enclosed by double membranes.

Chemistry for Biologists: Photosynthesis

What scientists have learned is that two general kinds of reactions are involved in photosynthesis: the light reactions and the dark reactions. Light reactions, as their name suggests, can take place only in the presence of sunlight. In those reactions, light energy is used to generate certain kinds of energy-rich compounds. These compounds do not themselves become part of the final carbohydrate product. Instead, they are used to "carry" energy from one compound to another in the process of photosynthesis.

C4 photosynthesis: how some plants avoid photorespiration

Photosynthesis is the process by which green plants and certain types of bacteria make carbohydrates, beginning only with carbon dioxide (CO 2 ) and water (H 2 O)

So we can summarize by saying that the photosynthetic plantstrap solar energy to form ATP and NADPH (Light Phase) and thenuse these as the energy source to make carbohydrates and otherbiomolecules from carbon dioxide and water (Dark Phase),simultaneously releasing oxygen in to the atmosphere. Thechemoheterotrophic animals reverse this process by using theoxygen to degrade the energy-rich organic products ofphotosynthesis to CO2 and water in order to generate ATP fortheir own synthesis of biomolecules.

Photosynthesis converts these energy- depleted compounds (ADPand NADP+) back to the high energy forms (ATP and NADPH) and theenergy thus produced in this chemical form is utilized to drivethe chemical reactions necessary for synthesis of sugars andother carbon containing compounds (e.g., proteins, fats). Theproduction of high energy ATP and NADPH in plants occurs in whatis known as Light Phase Reactions (Z Scheme) (requiressunlight). The energy releasing reactions which converts themback to energy-depleted ADP and NADP is known as Dark PhaseReactions (Calvin Cycle) (does not require light) in whichthe synthesis of glucose and other carbohydrates occurs.

photosynthesis notes - Biology Junction

In the last video we discovered what seems like a problem with the Calvin Cycle.

Anaerobic photosynthetic bacteria is a group of bacteria that do not produce oxygen during photosynthesis and only photosynthesize in environments that are devoid of oxygen. These bacteria use carbon dioxide and a substrate such as hydrogen sulfide to make carbohydrates. They have bacteriochlorophylls and other photosynthetic pigments that are similar to the chlorophylls used by higher plants. But, in contrast to higher plants, algae and cyanobacteria, the anaerobic photosynthetic bacteria have just one photosystem that is similar to PS-I. These bacteria likely represent a very ancient photosynthetic microbe.

In the light reactions of photosynthesis, light energy excites photosynthetic pigments to higher energy levels and this energy is used to make two high energy compounds, ATP (adenosine triphosphate) and NADPH ( nicotinamide adenine dinucleotide phosphate). ATP and NADPH are consumed during the subsequent dark reactions in the synthesis of carbohydrates.

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Chemistry for Biologists: Photosynthesis - The Royal …

I should point out that both the photo and the synthesis parts of photosynthesis aremultiple step reactions. Quite a number of steps are involved in separating hydrogen andelectrons from oxygen in water. Similarly, quite a number of step are involved in removingoxygen from carbon dioxide and incorporating hydrogen and additional electrons into thecompound. Also, the carbon dioxide is not used to create a new compound as such, butinstead, the carbon is incorporated into existing carbon-containing compounds in a waythat makes them larger than they were before.

plants photosynthesis? | Yahoo Answers

The carbohydrates are the compounds which provide energy to living cells. They are compounds of carbon, hydrogen and oxygen with a ratio of two hydrogens for every oxygen atom. The carbohydrates we use as foods have their origin in the photosynthesis of plants. They take the form of , , and .

Photosynthesis - humans, body, used, water, process, …

photosynthesis , process in which green plants, algae, and cyanobacteria utilize the energy of sunlight to manufacture carbohydrates from carbon dioxide and water in the presence of chlorophyll. Some of the plants that lack chlorophyll, e.g., the , secure their nutrients from organic material, as do animals, and a few bacteria manufacture their own carbohydrates with hydrogen and energy obtained from inorganic compounds (e.g., hydrogen sulfide) in a process called . However, the vast majority of plants contain chlorophyll—concentrated, in the higher land plants, in the leaves.

In these plants water is absorbed by the roots and carried to the leaves by the xylem, and carbon dioxide is obtained from air that enters the leaves through the stomata and diffuses to the cells containing chlorophyll. The green pigment is uniquely capable of converting the active energy of light into a latent form that can be stored (in food) and used when needed.

The Photosynthetic Process

The initial process in photosynthesis is the decomposition of water (HO) into oxygen, which is released, and hydrogen; direct light is required for this process. The hydrogen and the carbon and oxygen of carbon dioxide (CO) are then converted into a series of increasingly complex compounds that result finally in a stable organic compound, glucose (CHO), and water. This phase of photosynthesis utilizes stored energy and therefore can proceed in the dark. The simplified equation used to represent this overall process is 6CO+12HO+energy=CHO+6O+6HO. In general, the results of this process are the reverse of those in respiration, in which carbohydrates are oxidized to release energy, with the production of carbon dioxide and water.

The intermediary reactions before glucose is formed involve several enzymes, which react with the coenzyme ATP (see ) to produce various molecules. Studies using radioactive carbon have indicated that among the intermediate products are three-carbon molecules from which acids and amino acids, as well as glucose, are derived. This suggests that fats and proteins are also products of photosynthesis. The main product, glucose, is the fundamental building block of carbohydrates (e.g., sugars, starches, and cellulose). The water-soluble sugars (e.g., sucrose and maltose) are used for immediate energy. The insoluble starches are stored as tiny granules in various parts of the plant—chiefly the leaves, roots (including tubers), and fruits—and can be broken down again when energy is needed. Cellulose is used to build the rigid cell walls that are the principal supporting structure of plants.

Importance of Photosynthesis

Animals and plants both synthesize fats and proteins from carbohydrates; thus glucose is a basic energy source for all living organisms. The oxygen released (with water vapor, in transpiration) as a photosynthetic byproduct, principally of phytoplankton, provides most of the atmospheric oxygen vital to respiration in plants and animals, and animals in turn produce carbon dioxide necessary to plants. Photosynthesis can therefore be considered the ultimate source of life for nearly all plants and animals by providing the source of energy that drives all their metabolic processes.

Bibliography

See I. Asimov, (1969); R. M. Devlin and A. V. Barker, (1972); O. Morton, (2009).

Photosynthesis - Arboretum De Villardebelle

Photosynthesis is the process by which green plants and certain types of bacteria make carbohydrates, beginning only with carbon dioxide (CO2) and water (H2O). Carbohydrates are complex chemical compounds that occur widely in plants and that serve as an important food source for animals. Sugar, starch, and cellulose are among the most common carbohydrates. The energy needed to make photosynthesis possible comes from sunlight, which explains the term photo ("light") synthesis ("to make"). The absorption of sunlight in plants takes place in specific molecules known as chlorophyll (KLOR-uh-fill) that give plants their green color.

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