AP BIO CH 10

absorption spectrum

absorption spectrum

The range of a pigment's ability to absorb various wavelengths of light.

action spectrum

A graph that depicts the relative effectiveness of 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. Autotrophs use energy from the sun or from the oxidation of inorganic substances to make organic molecules from inorganic ones.

bundle-sheath cell

A type of photosynthetic cell arranged into tightly packed sheaths around the veins of a leaf.

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.

C4 plant

A plant that prefaces the Calvin cycle with reactions that incorporate CO2 into a four-carbon compound, the end product of which supplies CO2 for the Calvin cycle.

Calvin cycle

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

CAM plant

A plant that uses crassulacean acid metabolism, an adaptation for photosynthesis in arid conditions, first discovered in the family Crassulaceae. Carbon dioxide entering open stomata during the night is converted into organic acids, which release CO2 for the Calvin cycle during the day, when stomata are closed.

carbon fixation

The incorporation of carbon from CO2 into an organic compound by an autotrophic organism (a plant, another photosynthetic organism, or a chemoautotrophic bacterium).

carotenoid

An accessory pigment, either yellow or orange, in the chloroplasts of plants. By absorbing wavelengths of light that chlorophyll cannot, carotenoids broaden the spectrum of colors that can drive photosynthesis.

chlorophyll

A green pigment located within the chloroplasts of plants. Chlorophyll a can participate directly in the light reactions, which convert solar energy to chemical energy.

chlorophyll a

A type of blue-green photosynthetic pigment that participates directly in the light reactions.

chlorophyll b

A type of yellow-green accessory photosynthetic pigment that transfers energy to chlorophyll a.

crassulacean acid metabolism (CAM)

A type of metabolism in which carbon dioxide is taken in at night and incorporated into a variety of organic acids.

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 oxygen.

electromagnetic spectrum

The entire spectrum of radiation ranging in wavelength from less than a nanometer to more than a kilometer.

glyceraldehyde-3-phosphate (G3P)

The carbohydrate produced directly from the Calvin cycle.

heterotroph

An organism that obtains organic food molecules by eating other organisms or their by-products.

light reactions

The steps in photosynthesis that occur on the thylakoid membranes of the chloroplast and that convert solar energy to the chemical energy of ATP and NADPH, evolving oxygen in the process.

light-harvesting complex

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

mesophyll

The ground tissue of a leaf, sandwiched between the upper and lower epidermis and specialized for photosynthesis.

mesophyll cell

A loosely arranged photosynthetic cell located between the bundle sheath and the leaf surface.

NADP+

Nicotinamide adenine dinucleotide phosphate, an acceptor that temporarily stores energized electrons produced during the light reactions.

non-cyclic electron flow

A route of electron flow during the light reactions of photosynthesis that involves both photosystems and produces ATP, NADPH, and oxygen. The net electron flow is from water to NADP+.

PEP carboxylase

An enzyme that adds carbon dioxide to phosphoenolpyruvate (PEP) to form oxaloacetate.

photon

A quantum, or discrete amount, of light energy.

photophosphorylation

The process of generating ATP from ADP and phosphate by means of a proton-motive force generated by the thylakoid membrane of the chloroplast during the light reactions of photosynthesis.

photorespiration

A metabolic pathway that consumes oxygen, releases carbon dioxide, generates no ATP, and decreases photosynthetic output; generally occurs on hot, dry, bright days, when stomata close and the oxygen concentration in the leaf exceeds that of carbon dioxide.

photosynthesis

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

photosystem

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

photosystem I

One of two light-capturing units in a chloroplast's thylakoid membrane; it has two molecules of P700 chlorophyll a at its reaction center.

photosystem II

One of two light-capturing units in a chloroplast's thylakoid membrane; it has two molecules of P680 chlorophyll a at its reaction center.

primary electron acceptor

A specialized molecule sharing the reaction center with the pair of reaction-center chlorophyll a molecules; it accepts an electron from one of these two chlorophylls.

reaction center

Complex of proteins associated with two special chlorophyll a molecules and a primary electron acceptor. Located centrally in a photosystem, this complex triggers the light reactions of photosynthesis. Excited by light energy, one of the chlorophylls donates an electron to the primary electron acceptor, which passes an electron to an electron transport chain.

rubisco

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

spectrophotometer

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

stoma

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.

stroma

The fluid of the chloroplast surrounding the thylakoid membrane; involved in the synthesis of organic molecules from carbon dioxide and water.

thylakoid

A flattened membrane sac inside the chloroplast, used to convert light energy to chemical energy.

visible light

That portion of the electromagnetic spectrum detected as various colors by the human eye, ranging in wavelength from about 380 nm to about 750 nm.

wavelength

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