Key Terms

absorption spectrum
range of wavelengths of electromagnetic radiation absorbed by a given substance
antenna protein
pigment molecule that directly absorbs light and transfers the energy absorbed to other pigment molecules
Calvin cycle
light-independent reactions of photosynthesis that convert carbon dioxide from the atmosphere into carbohydrates using the energy and reducing power of ATP and NADPH
carbon fixation
process of converting inorganic CO2 gas into organic compounds
carotenoid
photosynthetic pigment that functions to dispose of excess energy
chemoautotroph
organism that can build organic molecules using energy derived from inorganic chemicals instead of sunlight
chlorophyll a
form of chlorophyll that absorbs violet-blue and red light and consequently has a bluish-green color; the only pigment molecule that performs the photochemistry by getting excited and losing an electron to the electron transport chain
chlorophyll b
accessory pigment that absorbs blue and red-orange light and consequently has a yellowish-green tint
chloroplast
organelle in which photosynthesis takes place
cytochrome complex
group of reversibly oxidizable and reducible proteins that forms part of the electron transport chain between photosystem II and photosystem I
electromagnetic spectrum
range of all possible frequencies of radiation
electron transport chain
group of proteins between PSII and PSI that pass energized electrons and use the energy released by the electrons to move hydrogen ions against their concentration gradient into the thylakoid lumen
granum
stack of thylakoids located inside a chloroplast
heterotroph
organism that consumes organic substances or other organisms for food
light harvesting complex
complex that passes energy from sunlight to the reaction center in each photosystem; it consists of multiple antenna proteins that contain a mixture of 300–400 chlorophyll a and b molecules as well as other pigments like carotenoids
light-dependent reaction
first stage of photosynthesis where certain wavelengths of the visible light are absorbed to form the two energy-carrying molecules, ATP and NADPH
light-independent reaction
second stage of photosynthesis, though which carbon dioxide is used to build carbohydrate molecules using energy from ATP and NADPH
mesophyll
middle layer of chlorophyll-rich cells in a leaf
P680
reaction center of photosystem II
P700
reaction center of photosystem I
photoact
ejection of an electron from a reaction center using the energy of an absorbed photon
photoautotroph
organism capable of producing its own organic compounds from sunlight
photon
distinct quantity or packet of light energy
photosystem
group of proteins, chlorophyll, and other pigments that are used in the light-dependent reactions of photosynthesis to absorb light energy and convert it into chemical energy
photosystem I
integral pigment and protein complex in thylakoid membranes that uses light energy to transport electrons from plastocyanin to NADP+ (which becomes reduced to NADPH in the process)
photosystem II
integral protein and pigment complex in thylakoid membranes that transports electrons from water to the electron transport chain; oxygen is a product of PSII
pigment
molecule that is capable of absorbing certain wavelengths of light and reflecting others (which accounts for its color)
primary electron acceptor
pigment or other organic molecule in the reaction center that accepts an energized electron from the reaction center
reaction center
complex of chlorophyll molecules and other organic molecules that is assembled around a special pair of chlorophyll molecules and a primary electron acceptor; capable of undergoing oxidation and reduction
reduction
gain of electron(s) by an atom or molecule
spectrophotometer
instrument that can measure transmitted light and compute the absorption
stoma
opening that regulates gas exchange and water evaporation between leaves and the environment, typically situated on the underside of leaves
stroma
fluid-filled space surrounding the grana inside a chloroplast where the light-independent reactions of photosynthesis take place
thylakoid
disc-shaped, membrane-bound structure inside a chloroplast where the light-dependent reactions of photosynthesis take place; stacks of thylakoids are called grana
thylakoid lumen
aqueous space bound by a thylakoid membrane where protons accumulate during light-driven electron transport
wavelength
distance between consecutive points of equal position (two crests or two troughs) of a wave in a graphic representation; inversely proportional to the energy of the radiation