Chapter 8 – Photosynthesis Vocabulary

A comprehensive set of key vocabulary terms covering the chemistry, structures, pigments, pathways, enzymes, and variations of photosynthesis as presented in Chapter 8 lecture notes.

Photosynthesis

Process by which green plants convert light energy, CO₂, and H₂O into glucose and O₂.

6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂

Overall balanced chemical equation for photosynthesis in plants.

Jan Baptista van Helmont

17th-century scientist who showed plant mass does not come solely from soil (willow tree experiment).

Joseph Priestly

Discovered plants restore 'something' (O₂) to air through his mint-and-candle experiment (1771).

Jan Ingenhousz

Proposed that sunlight splits CO₂ into C and O₂ during photosynthesis (late 1700s).

F.F. Blackman

Early 20th-century scientist who distinguished light-dependent and light-independent reactions.

C.B. van Niel

Showed some bacteria use H₂S, not H₂O, and formulated generalized photosynthesis equation.

Robin Hill

Demonstrated isolated chloroplasts use light energy to reduce NADP⁺ (Hill reaction).

Chloroplast

Double-membraned organelle where photosynthesis occurs in plants and algae.

Thylakoid Membrane

Internal chloroplast membrane housing chlorophyll and photosystems; site of light reactions.

Grana

Stacks of flattened thylakoid sacs within chloroplasts.

Stroma Lamellae

Membranous connections linking grana stacks.

Stroma

Fluid matrix surrounding thylakoids; site of Calvin cycle.

Light-Dependent Reactions

Stage that captures light to produce ATP and NADPH while splitting water to release O₂.

Calvin Cycle

Light-independent set of reactions that fix CO₂ into carbohydrates using ATP and NADPH.

Photon

Discrete packet of light energy whose energy is inversely proportional to wavelength.

Photoelectric Effect

Ejection of an electron from a molecule when it absorbs a photon.

Absorption Spectrum

Range and efficiency of wavelengths absorbed by a pigment.

Chlorophyll a

Primary photosynthetic pigment that directly converts light energy to chemical energy.

Chlorophyll b

Accessory pigment absorbing additional wavelengths and passing energy to chlorophyll a.

Carotenoids

Accessory pigments with alternating double bonds that absorb wide energy range and act as antioxidants.

Phycobiloproteins

Light-harvesting pigments found in cyanobacteria and some algae, efficient in low light.

Porphyrin Ring

Light-absorbing head of chlorophyll containing a central Mg²⁺ ion.

Photosystem

Cluster of pigments and proteins that captures light and channels energy to a reaction center.

Antenna Complex

Array of hundreds of accessory pigment molecules that funnel energy to reaction center chlorophylls.

Reaction Center

Pair of chlorophyll a molecules that transfer excited electrons out of the photosystem.

Photosystem I (P700)

Photosystem that ultimately reduces NADP⁺ to NADPH.

Photosystem II (P680)

Photosystem that oxidizes water and initiates the noncyclic electron flow.

Cyclic Photophosphorylation

Electron flow using a single photosystem that produces ATP but no NADPH or O₂.

Noncyclic Photophosphorylation

Electron flow through both photosystems generating ATP, NADPH, and O₂.

b₆-f Complex

Protein complex that transfers electrons between photosystems and pumps protons to form gradient.

Plastoquinone (PQ)

Mobile electron carrier that moves electrons from PSII to the b₆-f complex.

Plastocyanin (PC)

Copper-containing protein transferring electrons from b₆-f complex to PSI.

Ferredoxin (Fd)

Iron-sulfur protein that moves electrons from PSI to NADP⁺ reductase.

NADP⁺ Reductase (FNR)

Enzyme reducing NADP⁺ to NADPH using electrons from ferredoxin.

Chemiosmosis

ATP synthesis driven by a proton gradient across a membrane.

ATP Synthase

Membrane enzyme that synthesizes ATP as protons flow through it.

Carbon Fixation

Incorporation of CO₂ into organic molecules, first step of Calvin cycle.

Ribulose-1,5-bisphosphate (RuBP)

Five-carbon CO₂ acceptor molecule in Calvin cycle.

Ribulose Bisphosphate Carboxylase/Oxygenase (Rubisco)

Enzyme catalyzing CO₂ fixation to RuBP; can also add O₂ (photorespiration).

3-Phosphoglycerate (PGA)

First stable three-carbon product of CO₂ fixation in Calvin cycle.

Glyceraldehyde-3-phosphate (G3P)

Three-carbon sugar output of Calvin cycle used to make glucose, sucrose, or starch.

Photorespiration

Rubisco-catalyzed addition of O₂ to RuBP, wasting energy and carbon.

C₃ Photosynthesis

Calvin cycle pathway producing a three-carbon PGA; common in most plants.

C₄ Photosynthesis

Spatially separated CO₂ fixation pathway producing four-carbon oxaloacetate before Calvin cycle.

PEP Carboxylase

Enzyme in C₄/CAM plants that fixes CO₂ to phosphoenolpyruvate with high CO₂ affinity.

Bundle-Sheath Cells

Inner leaf cells where C₄ plants decarboxylate malate and run the Calvin cycle.

CAM Photosynthesis

Temporal separation pathway storing CO₂ at night as organic acids and releasing it by day.

Oxaloacetate

Four-carbon acid initially formed in C₄/ CAM CO₂ fixation.

Malate

Four-carbon compound transporting CO₂ from mesophyll to bundle-sheath cells in C₄ plants.

Sucrose

Main transport sugar in plants, synthesized from G3P-derived glucose and fructose.

Starch

Insoluble glucose polymer stored in chloroplasts for later energy use.

Antenna Pigments

Accessory pigments that expand the range of light absorption for the photosystem.

Electrochemical Gradient

Combined charge and concentration difference of protons across thylakoid membrane used for ATP production.

Z Scheme

Diagram depicting energy changes of electrons as they move through photosystems II and I.