2.5.5: Key Terms
- Page ID
- 97025
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- absorption spectrum
- range of wavelengths of electromagnetic radiation absorbed by a given substance
- antenna protein
- pigment molecule that directly absorbs light and transfers the energy absorbed to other pigment molecules
- Calvin cycle
- light-independent reactions of photosynthesis that convert carbon dioxide from the atmosphere into carbohydrates using the energy and reducing power of ATP and NADPH
- carbon fixation
- process of converting inorganic CO2 gas into organic compounds
- carotenoid
- photosynthetic pigment (yellow-orange-red) that functions to dispose of excess energy
- chemoautotroph
- organism that can build organic molecules using energy derived from inorganic chemicals instead of sunlight
- chlorophyll a
- form of chlorophyll that absorbs violet-blue and red light and consequently has a bluish-green color; the only pigment molecule that performs the photochemistry by getting excited and losing an electron to the electron transport chain
- chlorophyll b
- accessory pigment that absorbs blue and red-orange light and consequently has a yellowish-green tint
- chloroplast
- organelle in which photosynthesis takes place
- cytochrome complex
- group of reversibly oxidizable and reducible proteins that forms part of the electron transport chain between photosystem II and photosystem I
- electromagnetic spectrum
- range of all possible frequencies of radiation
- electron transport chain
- group of proteins between PSII and PSI that pass energized electrons and use the energy released by the electrons to move hydrogen ions against their concentration gradient into the thylakoid lumen
- granum
- stack of thylakoids located inside a chloroplast
- heterotroph
- organism that consumes organic substances or other organisms for food
- light harvesting complex
- complex that passes energy from sunlight to the reaction center in each photosystem; it consists of multiple antenna proteins that contain a mixture of 300 to 400 chlorophyll a and b molecules as well as other pigments like carotenoids
- light-dependent reaction
- first stage of photosynthesis where certain wavelengths of the visible light are absorbed to form two energy-carrying molecules (ATP and NADPH)
- light-independent reaction
- second stage of photosynthesis, through which carbon dioxide is used to build carbohydrate molecules using energy from ATP and NADPH
- mesophyll
- middle layer of chlorophyll-rich cells in a leaf
- P680
- reaction center of photosystem II
- P700
- reaction center of photosystem I
- photoact
- ejection of an electron from a reaction center using the energy of an absorbed photon
- photoautotroph
- organism capable of producing its own organic compounds from sunlight
- photon
- distinct quantity or “packet” of light energy
- photosystem
- group of proteins, chlorophyll, and other pigments that are used in the light-dependent reactions of photosynthesis to absorb light energy and convert it into chemical energy
- photosystem I
- integral pigment and protein complex in thylakoid membranes that uses light energy to transport electrons from plastocyanin to NADP+ (which becomes reduced to NADPH in the process)
- photosystem II
- integral protein and pigment complex in thylakoid membranes that transports electrons from water to the electron transport chain; oxygen is a product of PSII
- pigment
- molecule that is capable of absorbing certain wavelengths of light and reflecting others (which accounts for its color)
- primary electron acceptor
- pigment or other organic molecule in the reaction center that accepts an energized electron from the reaction center
- reaction center
- complex of chlorophyll molecules and other organic molecules that is assembled around a special pair of chlorophyll molecules and a primary electron acceptor; capable of undergoing oxidation and reduction
- reduction
- gain of electron(s) by an atom or molecule
- spectrophotometer
- instrument that can measure transmitted light and compute the absorption
- stoma
- opening that regulates gas exchange and water evaporation between leaves and the environment, typically situated on the underside of leaves
- stroma
- fluid-filled space surrounding the grana inside a chloroplast where the light-independent reactions of photosynthesis take place
- thylakoid
- disc-shaped, membrane-bound structure inside a chloroplast where the light-dependent reactions of photosynthesis take place; stacks of thylakoids are called grana
- thylakoid lumen
- aqueous space bound by a thylakoid membrane where protons accumulate during light-driven electron transport
- wavelength
- distance between consecutive points of equal position (two crests or two troughs) of a wave in a graphic representation; inversely proportional to the energy of the radiation