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| Photosynthesis | The conversion of light energy to chemical energy that is stored in glocose or other organic compounds; occurs in plants, algae, and certian prokaryotes. |
| Autotrophs | An organism that obtains organic food molecules without eating other organisms or substances derrived from other organisms. These organisms use energy from the sun or from the oxidation of inorganic substances to make organic molecules form inorganic ones. |
| Heterotrophs | An organism that obtains organic food molecules by eating other organisms or their by-products. |
| Chlorophyll | A green pigment located within the chloroplasts of plants. Chlorophyll a can participate directly in the light reactions, which convert solar energy to chemical energy. |
| Mesophyll | The ground tissue of a leaf, sandwiched between the upper and lower epidermis and specialized for photosynthesis. |
| Stomata (singular, stoma) | A microscopic pore surrounded by guard cells in the epidermis of leaves and stems that allows gas exchange between the environment and the interior of the plant. |
| Light Reactions | The steps in photosynthesis that occur on the thylakoid membranes of the chloroplast and that convert solar energy to the chemical enery of ATP and NADPH, evolving oxygen in the process. (The photo part of photosynthesis). |
| Calvin Cycle | The second og two major stages in photosynthesis (following the light reactions), involving atmospheric carbon dioxide fixation and reduction of the fixed carbon in to carbohydrates. (The synthesis part of photosynthesis). |
| NADP+ | (Nicotinamide adenine dinucleotide phosphate) An electron accpetor that temporarily stores energized electrons produced during the light reactions. |
| Photophosphorylation | The process of generating ATP from ADP and phosphate by means of a proton-motive force generated by the thylakoid membrane of the chloroplast during the light reactions of photosynthesis. |
| Carbon Fixation | The incorporation of carbon from carbon dioxide into an organic compound by an autotrophic organism (a plant, another photosynthetic organism, or a chemoautotrophic bacterium). |
| Wavelength | The distance between crests of waves, such as those of the electromagnetic spectrum. |
| Electromagnetic Spectrum | The entire spectrum of radiation ranging in wavelength from less than a nanometer to more than a kilometer. |
| Visible Light | The portion of the electromagnetic spectrum detected as various colors by the human eye; ranging in wavelength from about 380 nm to about 750 nm. |
| Photons | A quantum, or discrete amount, of light energy. |
| Spectrophotometer | An instrument that measures the proportions of light of different wavelengths absorbed and transmitted by a pigment solution. |
| Absorption Spectrum | The range of a pigment's ability to absorb various wavelengths of light. |
| Chlorophyll a | A type of blue-green photosynthetic pigment that participates directly in light reactions. |
| Chlorophyll b | A type of yellow-green accessory pigment that transfers energy to chlorophyll a |
| Carotenoid | An accessory pigment, either yellow or orange, in the chloroplasts of plants. By absorbing wavelengths of light that chlorophyll cannot, carotenoids broaden the spectrum of colors that can drive photosynthesis. |
| Photosystems | The light-harvesting unit in photosynthesis, located on the thylakoid membrane of the chloroplast and consisting of the antenna complex, the reaction-center chlorophyll a, and the primary electron acceptor. There are two types of photosystems, I and II; they absorb light best at different wavelengths. |
| Reaction Center | The chlorophyll a molecule and the primary electron acceptor in a photosystem; they trigger the light reactions of photosynthesis. The chlorophyll donates an electron, excited by light energy, to the primary electron acceptor, which passes an electron to an electron transport chain. |
| Primary Electron Acceptor | A specialized molecule sharing the reaction center with the chlorophyll a molecule; it accepts an electron from the chlorophyll a molecule. |
| Photosystem I | One of two light-harvesting units of a chloroplast's thylakoid membrane; it uses the P700 reaction-center chlorophyll. |
| Photosystem II | One of two light-harvesting units of a chloroplast's thylakoid membrane; it uses the P680 reaction-center chlorophyll. |
| Noncyclic Electron Flow | A route of electron flow during the light reactions of photosynthesis that involves both photosystems and produces ATP, NADPH, and oxygen. The net electron flow is from water to NADP+. |
| Cyclic Electron Flow | A route of electron flow during the light reactions of photosynthesis that involves only photosystem I and that produces ATP but not NADPH or oxygen. |
| Cyclic Photophosphorylation | The generation of ATP by cyclic electron flow. |
| G3P | (Glyceraldehyde-3-phosphate) The carbohydrate produced directly from the Calvin cycle. |
| Rubisco | Ribulose carboxylase, the enzyme that catalyzes the first step of the Calvin cycle (the addition of carbon dioxide to RuBP, or ribulose bisphosphate). |
| C3 Plants | A plant that uses the Calvin cycle for the initial steps that incorporate carbon dioxide into organic material, forming a three-carbon compound as the first stable intermediate. |
| Photorespiration | A metabolic pathway that consumes oxygen, releases carbon dioxide, generates no ATP, and decreases photosynthetic output; generally occurs on hot, dry, bright days, when stomata close and the oxygen concentration in the leaf exceeds that of carbon dioxide. |
| C4 Plants | A plant that prefaces the Calvin cycle with reactions that incorporate carbon-dioxide into four-carbon compounds, the end product of which supplies carbon dioxide for the Calvin cycle. |
| Bundle-Sheath Cell | A type of photosynthetic cell arranged into tightly packed sheaths around the veins of a leaf. |
| Mesophyll Cell | A loosely arranged photosynthetic cell located between the bundle sheath and the leaf surface. |
| PEP Carboxylase | An enzyme that adds carbon dioxide to phosphoenolpyruvate (PEP) to form oxaloacetate. |
| CAM | (Crassulacean acid metabolism) A type of metabolism in which carbon dioxide is taken in at night and incorporated into a variety of organic acids. |
| CAM Plants | A plant that uses crassulacean acid metabolism, an adaptation for photosynthesis in arid conditions, first discovered in the family Crassulacae. Carbon dioxide entering open stomata during the night is converted into organic acids, which release carbon dioxide for the Calvin cycle during the day, when stomata are closed. |
