In ordinary language, people speak of “producing” or “using” energy. This refers to the fact that energy in concentrated form is useful for generating electricity, moving or heating objects, and producing light, whereas diffuse energy in the environment is not readily captured for practical use. Therefore, to produce energy typically means to convert some stored energy into a desired form—for example, the stored energy of water behind a dam is released as the water flows downhill and drives a turbine generator to produce electricity, which is then delivered to users through distribution systems. Food, fuel, and batteries are especially convenient energy resources because they can be moved from place to place to provide processes that release energy where needed. A system does not destroy energy when carrying out any process. However, the process cannot occur without energy being available. The energy is also not destroyed by the end of the process. Most often some or all of it has been transferred to heat the surrounding environment; in the same sense that paper is not destroyed when it is written on, it still exists but is not readily available for further use.
The three major components of photosynthesis are the antenna, the reaction center, and the site of recombination. The antenna, which is composed of chlorophyll molecules in plants, collects or “harvests” the light energy from the sun. The energy then goes through a number of stages of energy transfer until it is ready for the reaction center. In the reaction center, the energy is used to drive a charge separation reaction, which produces an electron and a so-called “electron hole” where the electron was removed from. Next, certain structures in the membrane of the cell recombine the charges, a process which creates usable electrochemical energy that is then stored in adenosine triphosphate molecules, also known as ATP.
Chemistry for Biologists: Photosynthesis
We will present photosynthesis in two parts: this page will discuss the reactions that convert light energy to chemical energy in the form of ATP and reduced electron carriers (NADH or NADPH). Both are needed for carbon fixation reactions (the reduction of inorganic carbon to make organic carbon molecules) presented in the next page. An important by-product of the light reactions is the generation of oxygen gas. In the chemical equation above, the oxygen atoms in water are bolded in red to show that these are the source of the oxygen atoms in oxygen gas. Oxygenic photosynthesis evolved to take electrons from water to make oxygen gas, and ultimately give the electrons to carbon dioxide to form organic (reduced) carbon molecules (food) – the exact reverse of aerobic respiration, which takes electrons from organic carbon molecules and ultimately gives them to oxygen gas to make water.
ENERGY CONSERVATION IN PHOTOSYNTHETIC ELECTRON TRANSPORT ..
Photosynthesis is a process where by energy from light is harvested and used to drive synthesis of organic carbohydrates from carbon dioxide and water. Photosynthesis takes place in chloroplasts and can be divided into two steps: light reactions which require light and dark reactions which do not require light. During light reaction, light energy is captured by photosystems and electrons are transferred among the electron receptors. ATP and NADPH are generated. During dark reactions, CO2 is fixed using ATP and NADPH generated by the light reactions and organic carbohydrates are synthesized via the Calvin Cycle. When the CO2 is first fixed into a 3 carbon compound 3PGA, it is called C3 pathways and these plants are called C3 plants. The disadvantage of C3 plants is that they undergo photorespiration and thus waste some energy gained in light reactions. C4 cycle is the pathway adopted by C4 plants to bypass photorespiration.
Energy transfer in photosynthesis.
The energy inherent in this gradient is used to synthesize ATP in the process of "oxidative phosphorylation." The same processes occur in photosynthesis and the chloroplast, the site of photosynthesis in plants and blue-green algae (but not in photosynthetic bacteria), is the analog of the mitochondrion in eukaryotes.Chapter 22 ("Electron Transport and Oxidative Phosphorylation") in Voet & Voet (3rd Edition) is one of the most important chapters in the entire text (at least in my opinion) and it would help to reread it as you look at the light reaction of photosynthesis in more detail over the next two lectures. The first step in photosynthesis is the interaction of light with chlorophyll molecules. The chemical structures of the various chlorophyll molecules are based upon the cyclic tetrapyrrole that is also seen in the heme group of globins and cytochromes. Various modifications of this group, namely ring saturation characteristics and substitutions on the rings provide a series of pigment molecules that, as a group, absorb effectively over the wavelength range of 400 nm - 700 nm, the spectrum of . It is the high degree of conjugation of these molecules that makes them so efficient as absorbers of visible light.
Accessory pigments absorb energy that chlorophyll a does not ..
In the case of photosynthetic pigments, however, a different event happens that is critical for the process of photosynthesis.
Rather than releasing energy, an excited electron in a photosynthetic pigment is removed from that molecule and transferred to another molecule where the electron is more stable.