topic 5 part 2

photosynthesis

The conversion of light energy into chemical energy stored in sugars or other organic compounds.

heterotrophs

Organisms that obtain organic molecules by eating other organisms or gathering substances from other organisms.

photoautotrophs

Organisms that use light energy to drive the synthesis of organic molecules from carbon dioxide and water.

chlorophyll

A green pigment in the chloroplast that participates in the light reactions of photosynthesis.

light reactions

The stage of photosynthesis that occurs on the thylakoid membranes and converts solar energy into ATP and NADPH, releasing oxygen in the process.

Calvin cycle

The stage of photosynthesis involving the fixation of CO2 and the reduction of the fixed carbon into carbohydrates.

NADP+

An electron acceptor that can temporarily store energized electrons produced during the light reactions.

photophosphorylation

The process of generating ATP from ADP and phosphate by chemiosmosis across the thylakoid membrane.

carbon fixation

The initial incorporation of carbon dioxide into an organic compound by an autotrophic organism.

wavelength

The distance between crests (or troughs) of waves.

electromagnetic spectrum

All of the wavelengths of electromagnetic radiation.

visible light

The portion of the electromagnetic spectrum that can be detected by the human eye.

photon

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.

pigment

A substance that absorbs visible light.

absorption spectrum

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

chlorophyll a

A photosynthetic pigment that participates directly in the light reactions.

chlorophyll b

An accessory photosynthetic pigment that transfers energy to chlorophyll a.

carotenoids

Accessory pigments, either yellow or orange, that absorb wavelengths of light that chlorophyll cannot and broaden the spectrum of colors driving photosynthesis.

action spectrum

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

reaction-center complex

A complex of proteins associated with a special pair of chlorophyll a molecules and a primary electron acceptor that triggers the light reactions of photosynthesis.

light-harvesting complex

A complex of proteins associated with pigment molecules that captures light energy and transfers it to reaction-center pigments in a photosystem.

primary electron acceptor

A specialized molecule sharing the reaction center with the chlorophyll a molecule; it accepts an electron from the chlorophyll a molecule.

photosystem I

One of two light-capturing units in a chloroplast's thylakoid membrane; it is the second photosystem involved in the light reactions

photosystem II

One of two light-capturing units in a chloroplast's thylakoid membrane; it is the first photosystem involved in the light reactions.

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.

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

The enzyme that catalyzes the first step of the Calvin cycle.

ribulose biphosphate

The five-carbon sugar to which CO2 is attached during the Calvin cycle.