Photosynthesis Vocabulary

Absorption Spectrum

the range of a pigment's ability to absorb various wavelengths of light; also a graph of such a range

Action Spectrum

a graph that profiles the relative effectiveness of a different wavelengths of radiation in driving a particular process

Autotroph

an organism that obtains organic food molecules without eating other organisms or substances derived from other organisms

CAM Plant

a plant that uses crassulacean acid metabolism an adaptation from photosynthesis in arid conditions; in this process, CO2 entering open stomata during the night is converted to organic acids, which release CO2 for the Calvin cycle during the day, when stomata are closed (ex. cactus, pineapples)

C3 Plant

a plant that uses the Calvin cycle for the initial steps that incorporate CO2 into organic material, forming a three-carbon compound as the first stable intermediate (ex. wheat, oats, rye)

C4 Plant

a plant in which the Calvin cycle is preceded by reactions that incorporate CO2 into a four-carbon compound, the end product of which supplies CO2 for the Calvin cycle (ex. corn, sugarcane, sorghum)

Calvin Cycle

the second of two major stages in photosynthesis (following the light reactions), involving fixation of atmospheric CO2 and reduction of the fixed carbon into carbohydrate

Carbon Fixation

the initial incorporation of carbon from CO2 into an organic compound by an autotrophic organism (a plant, another photosynthetic organism, or a chemoautotrophic prokaryote)

Carotenoid

an accessory pigment, either yellow or orange , in the chloroplast of plants and in some prokaryotes; by absorbing wavelengths of light that chlorophyll cannot, carotenoids broaden the spectrum of colors that can drive photosynthesis

Chlorophyll

a green pigment located in membranes within the chloroplasts of plants and algae and in the membranes of certain prokaryotes

Chlorophyll a

a photosynthetic pigment that participates directly in the light reactions, which convert solar energy to chemical energy

Chlorophyll b

an accessory photosynthetic pigment that transfers energy to chlorophyll a

Linear Electron Flow

a route of electron flow during the light reactions of photosynthesis that involves both photosystems (I and II) and produces ATP, NADPH and O2; the net electron flow is from H2O to NADP+

Decomposer

an organism that absorbs nutrient from nonliving organic material such as corpses, fallen plant material, and the wastes of living organisms and converts them to inorganic forms; a detritivore

Electromagnetic Spectrum

the entire spectrum of electromagnetic radiation, ranging in wavelength from less than a nanometer to more than a kilometer

Glyceraldehyde 3-phosphate (G3P)

a three-carbon carbohydrate that is the direct product of the Calvin cycle

Heterotroph

an organism that obtains organic food molecules by eating other organisms or substances derived from them

Light Reactions

the first of two major stages in photosynthesis (preceding the Calvin cycle); these reactions, which occur on the thylakoid membranes of the chloroplast or on membranes of certain prokaryotes, convert solar energy to the chemical energy of ATP and NADPH, releasing oxygen in the process

Light-Harvesting Complex

a complex of proteins associated with pigment molecules (including chlorophyll a, chlorophyll b, and carotenoids) that captures light energy and transfers it to reaction-center pigments in a photosystem

Mesophyll

leaf cells specialized for photosynthesis; in C3 and CAM plants, mesophyll cells are located between the upper and lower epidermis; in C4 plants, they are located between the bundle-sheath cells and the epidermis

NADP+

the oxidized form of nicotinamide adenine dinucleotide phosphate, an electron carrier that can accept electrons

NADPH

the reduced form of nicotinamide adenine dinucleotide phosphate; temporarily stores energized electrons produced during the light reactions; acts as "reducing power" that can be passed along to an electron acceptor, reducing it

Photon

a quantum, or discrete quantity, of light energy that behaves as if it were a particle

Photophosphorylation

the process of generating ATP from ADP and phosphate by means of chemiosmosis, using a proton-motive force generated across the thylakoid membrane of the chloroplast or the membrane of certain prokaryotes during the light reactions of photosynthesis

Photorespiration

a metabolic pathway that consumes oxygen and ATP releases carbon dioxide, and decreases photosynthetic output; photorespiration generally occurs on hot, dry, bright days, when the stomata close and the O2: CO2 ratio in the leaf increases, favoring the binding of O2 rather than CO2 by rubisco

Photosynthesis

the conversion of light energy to chemical energy that is stored in sugars or other organic compounds; occurs in plants, algae, and certain prokaryotes

Photosystem

a light-capturing unit located in the thylakoid membrane of chloroplast or in the membrane of some prokaryotes, consisting of a reaction-center complex surrounded by numerous light-harvesting complexes; there are two types of photosystems, I and II; they absorb light best at different wavelengths

Photosystem I (PSI)

a light-capturing unit in a chloroplast's thylakoid membrane or in the membrane of some prokaryotes; it has two molecules of P700 chlorophyll a at its reaction center

Photosystem II (PSII)

one of the two light-capturing units in a chloroplast's thylakoid membrane or in the the membrane of some prokaryotes; it has two molecules of P680 chlorophyll a at its reaction center

Primary Electron Acceptor

in the thylakoid membrane of a chloroplast or in the membrane of some prokaryotes, a specialized molecule that shares the reaction-center complex with a pair of chlorophyll a molecules and that accepts an electron from them

Producer

an organism that produces organic compounds from CO2 by harnessing light energy (in photosynthesis) or by oxidizing inorganic chemicals (in chemosynthetic reactions carried by out by some prokaryotes)

Reaction Center Complex

membrane-bound pigment-protein complexes that use light to catalyze a transmembrane electron transfer against a steep thermodynamic gradient

Rubisco

Ribulose bisphosphate (RuBP) carboxylase-oxygenase, the enzyme that normally catalyzes the first step of the Calvin cycle (the addition of CO2 to RuBP); when excess O2 is presenting or CO2 levels are low, rubisco can bind oxygen, resulting in photorespiration

Spectrophotometer

an instrument that measures the proportions of light of different wavelengths absorbed and transmitted by a pigment solution

Stomata

microscopic pores surrounded by guard cells in the epidermis of leaves and stems that allows gas exchange between the environment and the interior of the plant

Thylakoid

a flattened, membranous sac inside a chloroplast; thylakoids often exist in stacks called grana that are interconnected; their membranes contain molecular "machinery" used to convert light energy to chemical energy

Visible Light

that portion of the electromagnetic spectrum that can be detected as various colors by the human eye, ranging in wavelength from about 380 nm to about 740 nm

Wavelength

the distance between crests of waves, such as those of the electromagnetic spectrum