AP Biology Unit 3 Vocabulary - Chapter 8: Key Terms and Definitions

Absorption Spectrum

The range of a pigment's ability to absorb various wavelengths of light; also a graph of such a range.

Action Spectrum

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

Autotrophs

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 oxidation of inorganic substances to make organic molecules from inorganic ones.

Calvin Cycle

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

Carbon Fixtation

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

Chlorophyll

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

Electromagnetic Spectrum

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

G3P

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

Heterotrophs

An organism that obtains food molecules by eating other organisms or substances derived from them.

Light

The definition of light in science is electromagnetic radiation or energy that propagates as waves or oscillating photons through empty space.

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.

Light Reactions

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

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 O2. The net electron flow is from H2O to NADP+.

NADP+

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

Photons

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

Photophosphorylation

The process of generating ATP from ADP and phosphate by means of chemiosmosis

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.

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 numerous light-harvesting complexes. There are two types of photosystems, 1 and 2; they absorb light best at different wavelengths.

Photosystem 1

One of two light capturing units in a chloroplasts' thylakoid membrane or in the membrane of some prokaryotes; it has two molecules of P700 chlorophyll a at its reaction center.

Photosystem 2

One of two light capturing units in a chloroplasts' thylakoid membrane or in the membrane of some prokaryotes; it has two molecules of P680 chlorophyll a at its center.

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 there.

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 the light 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.

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.

Stroma

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

Thylakoids

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

Wavelength

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