AP Biology Chapter 10 Photosynthesis Vocabulary

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

autotroph

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

heterotroph

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

mesophyll

leaf cells specialized for photosynthesis

stomata

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

stroma

the dense fluid within the chloroplast surrounding the thylakoid membrane and containing ribosomes and DNA; involved in the synthesis of organic molecules from carbon dioxide and water

thylakoid

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

thylakoid space

the inside of a thylakoid

grana

stacks of thylakoid sacs within the chloroplast

chlorophyll

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

light reactions

the first of two major stages in photosynthesis. These, which occur on the thylakoid membranes of the chloroplast or on membranes of certain prokaryotes, convert solar energy to chemical energy of ATP and NADPH, releasing oxygen in the process

Calvin cycle

the second of two major stages in photosynthesis, involving fixation of atmospheric CO2 and reduction of the fixed carbon into carbohydrate

NADP+

nicotinamide adenine dinucleotide phosphate; an electron acceptor that, as NADPH, temporarily stores energized electrons produced during the light reactions

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 CO2 into an organic compound by an autotrophic organism (a plant, another photosynthetic organism, or a chemoautotrophic prokaryote)

wavelength

the distance between the crests of electromagnetic waves

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 380 nm to about 750 nm

photon

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

pigment

substance that absorbs visible light

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

action spectrum

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

chlorophyll b

an accessory photosynthetic pigment that ranchers energy to chlorophyll a

carotenoid

an accessory pigment, either yellow or orange, in the chloroplasts of plants and in some prokaryotes. By absorbing wavelengths of light that chlorophyll cannot, it broadens the spectrum of colors that can drive photosynthesis

photoprotection

a group of mechanisms, especially carotenoids, that help living organisms cope with molecular damage caused by sunlight

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 surrounded by by numerous light-harvesting complexes.

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, this complex triggers reactions of photosynthesis. Excited by light energy, the pair of chlorophylls donates an electron to the primary electron acceptor, which passes an electron to an electron transport chain.

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 II (PS II)

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 I (PS I)

a light-capturing units 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 (I and II) and produces ATP, NADPH, and O2. The net electron flow is from H2O 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 O2.

glyceraldehyde 3-phosphate (G3P)

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

rubisco

ribulose bisphosphate (RuBP) carboxylase, The enzyme that catalyzes the first step of the Calvin cycle (the addition of CO2 to RuBP).

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

photorespiration

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

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

bundle-sheath cell

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

PEP carboxylase

an enzyme that adds CO2 to phosphoenolpyruvate (PEP) to form oxaloacetate in mesophyll cells of C4 plants. It acts prior to photosynthesis.

CAM plant

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 CO2 for the Calvin cycle during the day, when stomata are closed.