Unit 2b: Metabolic Processes - Photosynthesis Flashcards
light-dependent reactions
In photosynthesis, the reactions in which light energy is captured and used in production of ATP and NADPH. In plants this involves the action of two linked photosystems.
light-independent reactions
In photosynthesis, the reactions of the Calvin cycle in which ATP and NADPH from the light-dependent reactions are used to reduce CO2 and produce organic compounds such as glucose. This involves the process of carbon fixation, or the conversion of inorganic carbon (CO2) to organic carbon (ultimately carbohydrates).
carbon fixation
The conversion of CO2 into organic compounds during photosynthesis; the first stage of the dark reactions of photosynthesis, in which carbon dioxide from the air is combined with ribulose 1,5-bisphosphate.
chlorophyll
The primary type of light-absorbing pigment in photosynthesis. Chlorophyll a absorbs light in the violet-blue and the red ranges of the visible light spectrum; chlorophyll b is an accessory pigment to chlorophyll a absorbing light in the blue and red-orange ranges. Neither pigment absorbs light in the green range , 500-600 nm.
stroma
In plants, a minute opening bordered by guard cells in the epidermis of leaves and stems; water passes out of the plant mainly through the stomata. (pl. stomata)
photosystems
An organized complex of chlorophyll, other pigments, and proteins that traps light energy as excited electrons. Plants have two linked photosystems in the thylakiod membrane of chloroplasts. Photosystem II passes an excited electron through an electron transport chain to photosystem I to replace an excited electron passed to NADPH. The electron lost from photosystem II is replaced by the oxidation of water.
photon
A particle of light having a discrete amount of energy. The wave concept of light explains the different colours of the spectrum, whereas the particle concept of light explains the energy transfer during photosynthesis.
pigments
A molecule that absorbs light.
photoelectric effect
The ability of a beam of light to excite electrons, creating an electrical current.
absorption spectrum
The relationship of absorbance vs. wavelength for a pigment molecule. This indicate which wavelengths are absorbed maximally by a pigment. For example, chlorophyll a absorbs most strongly in the violet-blue and red regions or the visible light spectrum.
action spectrum
A measure of the efficiency of different wavelengths of light for photosynthesis. In plants it corresponds to the absorption spectrum of chlorophylls.
carotenoid
Any of a group of accessory pigments found in plants; in addition to absorbing light energy, these pigments act as antioxidants, scavenging potential damaging free radical.
phycobiloprotein
A type of accessory pigment found in cyanobacteria and some algae. Complexes of phycobiloprotein are able to absorb light energy in the green range.
antenna complex
A complex of hundreds of pigment molecules in a photosystem that collects photons and feeds the light energy to a reaction center.
reaction center
A transmembrane protein complex in a photosystem that receives energy from the antenna complex exciting an electron that is passed to an acceptor molecule.
- primary photoevent (Light-Dependent Reactions)
A photon of light is captured by a pigment. This primary photoevent excites an electron within the pigment.
- charge separation (Light-Dependent Reactions)
This excitation energy is transferred to the reaction center, which transfers an energetic electron to an acceptor molecule, initiating electron transport.
- electron transport (Light-Dependent Reactions)
The excited electrons are shuttled along a series of electron carrier molecules embedded within the photosynthetic membrane. Several of them react by transporting protons across the membrane, generating a proton gradient. Eventually the electrons are used to reduce a final acceptor, NADPH.
- chemiosmosis (Light-Dependent Reactions)
The protons that accumulate on one side of the membrane now flow back across the membrane through ATP synthase where chemiosmotic synthesis of ATP takes place, just as it does in aerobic respiration.
noncyclic photophosphorylation
The set of light-dependent reactions of two plant photosystems, in which excited electrons are shuttled between the two photosystems, reducing a proton gradient that is used for the chemiosmotic synthesis of ATP. The electrons are used to reduce NADP to NADPH. Lost electrons are replaced by the oxidation of water producing O2.
- energy (Carbon Fixation: The Calvin Cycle)
ATP (provided by cyclic and noncyclic photophosphorylation) drives the endergonic reactions.
- reduction potential (Carbon Fixation: The Calvin Cycle)
NADPH (provided by photosystem I) provides a source of protons and the energetic electrons needed to bind them to carbon atoms. Much of the light energy captured in photosynthesis ends up invested in the energy-rich C-H bonds of sugar.
photophosphorylation
The phosphorylation of ADP to ATP using the energy of sunlight in the process of photosynthesis.
Calvin cycle
The dark reactions of C3 photosynthesis; also called the Calvin-Benson cycle.
