Bio 2300 Chapter 11

Chemotrophs

Organisms that obtain energy by oxidizing high-energy organic compounds like carbohydrates, fats, and proteins.

Photosynthetic organisms

Organisms that produce chemical energy and organic carbon used by chemotrophs by reducing CO2.

Photosynthesis

The process of converting light energy into chemical energy and using it to synthesize organic molecules.

Phototrophs

Organisms that convert solar energy into chemical energy (ATP and reduced NADPH).

Photoheterotrophs

Organisms that acquire energy from sunlight but depend on organic sources for reduced carbon (e.g., halobacteria).

Photoautotrophs

Organisms (plants, algae, and most photosynthetic bacteria) that use solar energy to synthesize organic molecules from CO2 and H2O.

Energy transduction reactions

The first major stage of photosynthesis where light energy is captured and converted to chemical energy.

Carbon assimilation reactions

Also known as carbon fixation reactions, this is the stage where carbohydrates are formed from CO2 and H2O.

Chloroplast

The photosynthetic organelle in eukaryotic cells; a mature leaf may contain 20–100.

Proplastids

Early organelles that can develop into specialized plastids depending on cell function.

Amyloplasts

Specialized plastids for storing starch.

Chromoplasts

Plastids that provide distinctive colors to flowers and fruits.

Proteinoplasts

Organelles derived from protoplastids for storing proteins.

Elaioplasts

Organelles derived from protoplastids for storing lipids.

Outer membrane

The exterior chloroplast membrane containing porins for the passage of small solutes.

Inner membrane

The membrane enclosing the stroma; it contains transport proteins for metabolites.

Stroma

A gel-like matrix inside the inner membrane full of enzymes for carbon, nitrogen, and sulfur assimilation.

Thylakoids

A third membrane system composed of flat, saclike structures in the stroma.

Grana

Stacks of thylakoids.

Stroma thylakoids

Long thylakoids that interconnect various grana.

Thylakoid lumen

The single continuous internal compartment enclosed by thylakoid membranes.

Carboxysomes

Polyhedral structures in cyanobacteria where carbon fixation reactions occur.

Photons

Particles of light that behave as indivisible packets of energy (quanta).

Photoexcitation

The first step of photosynthesis where a photon transfers energy to an electron, moving it to an excited state.

Absorption spectra

A description of the specific wavelengths of light absorbed by a particular pigment.

Resonance energy transfer

The process where energy from a photoexcited electron is transferred to an electron in an adjacent molecule.

Photochemical reduction

The essential transfer of an excited electron to another molecule to convert light to chemical energy.

Porphyrin ring

The central light-absorbing part of chlorophyll a and b.

Phytol side chain

A hydrophobic anchor that holds chlorophyll in the thylakoid membrane.

Bacteriochlorophyll

A subfamily of chlorophyll restricted to anoxygenic phototrophs.

Accessory pigments

Pigments that absorb photons chlorophyll cannot capture, such as carotenoids and phycobilins.

Carotenoids

Pigments (like β-carotene and lutein) that confer orange or yellow tints to leaves.

Phycobilins

Pigments found only in red algae (phycoerythrin) and cyanobacteria (phycocyanin).

Photosystems

Functional units of pigments and proteins including antenna pigments and a reaction center.

Special pair

Two chlorophyll a molecules in the reaction center that catalyze solar-to-chemical energy conversion.

Light-harvesting complex (LHC)

A collection of pigments that collects light energy and passes it to a photosystem.

Emerson enhancement effect

The phenomenon where combined wavelengths drive photosynthesis more efficiently than the sum of individual wavelengths.

Photosystem I (PSI)

A photosystem with an absorption maximum of 700 nm (P700).

Photosystem II (PSII)

A photosystem with an absorption maximum of 680 nm (P680).

Noncyclic electron flow

The unidirectional flow of electrons from water to NADP+.

Plastoquinone (QB)

An electron carrier in PSII that is reduced to plastoquinol (QBH2)

Pheophytin (Ph)

A chlorophyll a molecule lacking Mg2+ that acts as an early electron acceptor in PSII.

Oxygen-evolving complex

The portion of PSII that catalyzes water photolysis (splitting water into O2, protons, and electrons).

Cytochrome b6/f complex

An ETC complex that links PSII and PSI and establishes a proton gradient.

Plastocyanin (PC)

A mobile copper-containing protein that transfers electrons to PSI.

Chloroplast Q cycle

A cycle within the cytochrome b6/f complex that facilitates proton pumping.

Ferredoxin (Fd)

A mobile iron-sulfur protein in the stroma and the final electron acceptor for PSI.

Ferredoxin-NADP+ reductase (FNR)

The enzyme that transfers electrons from ferredoxin to NADP+ to produce NADPH.

Photophosphorylation

The generation of ATP driven by a proton gradient.

ATP synthase (CFOCF1)

The complex that uses the proton motive force to synthesize ATP.

Cyclic photophosphorylation

A process where PSI reducing power is diverted back into ATP synthesis rather than NADP+ reduction.

Calvin cycle

The main pathway for moving inorganic carbon into the biosphere, occurring in the stroma.

Stomata

Pores in leaves through which CO2 enters and O2 exits.

Rubisco

Ribulose-1,5-bisphosphate carboxylase/oxygenase; the enzyme that captures CO2.

Glyceraldehyde-3-phosphate (G3P)

The primary triose phosphate product of the Calvin cycle.

Thioredoxin

A protein reduced by ferredoxin that activates Calvin cycle enzymes in the light.

Rubisco activase

An enzyme that removes inhibitors from the rubisco active site.

Triose phosphate/phosphate translocator

An antiport system that exports triose phosphates to the cytosol in exchange for Pi (inorganic phosphate).

Isoenzymes (isozymes)

Different proteins (like the separate stromal and cytosolic forms) that perform the same enzymatic function.

Sucrose

The major carbohydrate used for transport to nonphotosynthetic parts of the plant.

Starch

The major storage carbohydrate, synthesized and kept in the chloroplast stroma.

Oxygenase activity

Rubisco's ability to add O2 instead of CO2, which decreases photosynthetic efficiency.

Glycolate pathway

Also called photorespiration; a light-dependent process that recovers 75% of carbon from phosphoglycolate.

Leaf peroxisome

The organelle where several steps of the glycolate pathway occur.

Hatch–Slack cycle

A CO2-concentrating pathway used by C4 plants to minimize photorespiration.

C3 plants

Plants where the first product of carbon fixation is the three-carbon 3-phosphoglycerate.

Bundle sheath cells

Isolated cells in C4 plants where the Calvin cycle is confined to prevent O2 interference.

Crassulacean acid metabolism (CAM)

An adaptive strategy where plants open stomata only at night to minimize water loss.