Chapter 10: Photosynthesis

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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.

Autotrophs

They sustain themselves without eating other organisms or substances derived from other organisms. They obtain CO2 and other inorganic materials from the environment. AKA producers.

Heterotrophs

Obtain their organic material by the second major mode of nutrition. Consumers.

Chlorophyll

The green pigment within chloroplasts. Light energy absorbed by this drives the synthesis of food molecules within the chloroplast.

Mesophyll

The tissue in the interior of the leaf.

Stomata

Microscopic pores that carbon dioxide enters the leaf through and oxygen exits.

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.

Calvin Cycle

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

NADP+

An acceptor that temporarily stores the energized electrons in the light reaction.

Photophosphorylation

A process where light reactions generate ATP by powering the addition of a phosphate group to ADP.

Carbon Fixation

The Calvin cycle begins by incorporating CO2 from the air into organic molecules already present in the chloroplast.

Wavelength

The distance between the crests of electromagnetic waves.

Electromagnetic Spectrum.

The entire range of radiation from gamma rays to radio waves.

Visible Light

The segment most important to life that ranges from 380 to 750 nm in wavelength.

Photons

A quantum, or discrete amount, of light energy.

Spectrophotometer

A machine that directs beams of light of different wavelengths through a solution of the pigment and measures the fraction of the light transmitted at each wavelenth. Measures the ability of a pigment to absorb various wavelengths of light.

Absorption Spectrum

A graph plotting a pigment's light absorption (the fraction not transmitted or reflected) versus wavelength.

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 tranfers energy to chlorophyll a.

Action Spectrum

Profiles the relative performance of the different wavelengths.

Carotenoids

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

Photosystems

The light-harvesting unit in photosynthesis, located on the thylakoid membrane of the chloroplast and consisting of the antenna complex, the reaction-center chlorophyll a, and the primary electron acceptor. There are two types of photosystems, I and II; they absorb light best at different wavelengths.

Reaction Center

The chlorophyll a molecule and the primary electron acceptor in a photsystem; they trigger the light reactions of photosynthesis. The chloroplyll donates an electron, excited by light energy, to the primary electron acceptor, which passes an electron to an electron transport chain.

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-harvestin units of a chloroplasts' thylakoid membrane, it uses the P700 reaction-center chlorophyll.

Photosystem II

Light-harvesting unit of a chloroplast's thylakoid membrane; it uses the P680 reaction-center chlorophyll.

Noncyclic Electron Flow

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

Noncyclic Photophosphorylation

The production of ATP by noncyclic electron flow.

Cyclic Electron Flow

A route of electron flow during the light reactions of photosyntheis that involves only photosystem I and that produces ATP but not NADPH or oxygen.

Cyclic Photophosphorylation

The generation of ATP by cyclic electron flow.

Glyceraldehyde-3-Phosphate (G3P)

The carbohydrate produced directly from the Calvin cycle.

C3 Plant

A plant that uses the initial steps that incorporate CO2 into organice material, forming a three-carbon compoud as the first stable intermediate.

C4 Plant

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

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.

Bundle-Sheath Cell

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

Mesophyll Cell

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

PEP Carboxylase

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

CAM Plant

A plant that uses crassulacean acid metabolism, an adaption for photosynthesis in arid conditions, first discovered in the family Crassulacae. 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.

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.

Rubisco

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

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