Campbell Biology, Ch. 10

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

autotrophs

an organism that obtains organic food molecules without eating other organisms; use energy from the sun or from oxidation of inorganic substances to make organic molecules from inorganic ones

heterotrophs

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

mesophyll

leaf cells specialized for photosynthesis

stomata

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

chlorophyll

a green pigment located in membranes within the chloroplasts of plants and algae and in the membranes of certain prokaryotes; participates directly in the light reactions, which convert solar energy to chemical energy

light reactions

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

calvin cycle

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

NADP plus

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

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

carbon fixation

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

wavelength

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

electromagnetic spectrum

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

visible light

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

photons

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

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; also a graph of such a range

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

action spectrum

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

carotenoids

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

photosystem

a light-capturing unit located in the thylakoid membrane of the chloroplast or in the membrane of some prokaryotes, consisting of a reaction-center complex surrounding numerous light-harvesting complexes; two types

reaction-center complex

a complex of proteins associated with a special pair of chlorophyll a molecules and a primary electron acceptor; located centrally in a photosystem and triggers the light reactions of photosynthesis

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

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

photosystem 2

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

photosystem 1

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

linear electron flow

a route of electron flow during the light reactions of photosynthesis that involves both photosystems (1 and 2) and produces ATP, NADPH, and oxygen; the net electron flow is from water to NADP plus

cyclic electron flow

a route of electron flow during the light reactions of photosynthesis that involves only one photosystem and that produces ATP but not NADPH or oxygen

glyceraldehyde 3-phosphate

a three-carbon carbohydrate that is the direct product of the calvin cycle; it is als an intermediate in glycolysis

rubisco

ribulose biphosphate carboxylase-oxygenase, the enzyme that normally catalyzes the first step of the calvin cycle

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 and ATP, releases carbon dioxide, and decreases photosynthetic output; generally occurs on hot, dry, bright days, when the stomata close and the oxygen to carbon dioxide ratio in the leaf increases, favoring the binding of oxygen rather than carbon dioxide by rubisco

C4 plants

a plant in which the calvin cycle is preceded by reactions that incorporate carbon dioxide into a four-carbon compound, the end product of which supplies carbon dioxide for the calvin cycle

bundle-sheath cells

in C4 plants, a type of photosynthetic cell arranged into tightly packed sheaths around the veins of a leaf

PEP carboxylase

an enzyme that adds carbon dioxide to phosphoenolpyruvate to form ozyloacetate in mesophyll cells of C4 plants; acts prior to photosynthesis

crassulacean acid metabolism

an adaptation for photosynthesis in arid conditions; in this process, a plant takes up carbon dioxide and incorporates it into a variety of organic acids at night; during the day, carbon dioxide is released from organic acids for use in the calvin cycle

CAM plants

a plant that uses crassulacean acid metabolism, an adaptation for photosynthesis in arid conditions; in this process, carbon dioxide entering open stomata during the night is converted to organic acids, which release carbon dioxide for the calvin cycle during the day, when stomata are closed