Ch8 Photosynthesis

Chlorophyll B

An accessory photosynthetic pigment that transfers energy to chlorophyll a.

NADP+

The oxidized form of nicotinamide adenine dinucleotide phosphate, an electron carrier that can accept electrons becoming NADPH. NAPH temporarily stores energized electrons produced during the light reactions.

Heterotroph

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

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, carotenoids broaden the spectrum of colors that can drive 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).

Photophosphorylation

The process of generating ATP from ADP and phosphate by means of chemiosmosis, using a proton

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.

Thylakoid

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.

Glyceraldehyde 3 phosphate

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

CAM plants

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.

Primary electron acceptor

In the thylakoid membrane of a chloroplast or in the membrane of some prokaryotes, a specialized molecule that shares the reaction

Photon

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

Reduction

The complete or partial addition of electrons to a substance involved in a redox reaction.

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 H20 to NADP+.

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.

Crassulacean acid metabolism (CAM)

An adaptation for photosynthesis in arid conditions, first discovered in the family Crassulaceae. In this process, a plant takes up CO2 at night when stomata are open and incorporates it into a variety of organic acids; during the day, when stomata are closed, CO2 is released from the organic acids for use in the Calvin cycle.

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.

C3 plants

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.

Visible light

That portion of the electromagnetic spectrum that can be detected as various colors by the human eye, running in wavelengths from about 380 nm to about 750 nm.

C4 plants

A plant in which the Calvin cycle is preceded by reactions that incorporate CO2 into a four

Wavelength

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

Chloroplast

An organelle found in plants and photosynthetic protists that absorbs sunlight and uses it to drive the synthesis of organic compounds from carbon dioxide and water.

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

Photosystem I (PS I)

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

Rubisco

Ribulose bisphosphate (RuBP0 carboxylase

Photorespiration

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

Spectrophotometer

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

Chlorophyll

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

Light reactions

The first of 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.

Mesophyll

Leaf cells specialized for photosynthesis. In C3 and CAM plants, mesophyll cells are located between the upper and lower epidermis; in C4 plants, they are located between the bundle sheath cells and the epidermis.

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.

Absorption Spectrum

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

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

Electromagnetic Spectrum

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

Calvin cycle

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

NADPH

The reduced form of nicotinamide adenine dinucleotide phosphate, which temporarily stores energized electrons produced during the light reactions. NADPH acts as “reducing power” that can be passed along to an electron acceptor, reducing it.

Photosystem

A light capturing unit located in the thylakoid membrane of the chloroplast or in the membrane of some prokaryotes, consisting of a reaction

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.

Stroma

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